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The evolution of branchiostegal rays in teleostome fishes McAllister, Don Evan 1964

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THE EVOLUTION OF BRANCHIOSTEGjrAL RAYS IN TELEOSTOME FISHES B  Donald Evan McAllister B. A . , University of British Columbia, 1955 M. A . , University of British Columbia, 1957  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF . DOCTOR OF PHILOSOPHY in the Department of Zoology  We accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA March, 1964  <  In the  r e q u i r e m e n t s f o r an  British  mission  for reference  for extensive  p u r p o s e s may  be  advanced  of  w i t h o u t my  written  Department  of  by  the  Library  this thesis  Head o f my  i s understood  permission.  Columbia,  fulfilment  of  University  of  s h a l l make i t f r e e l y  I further  agree for  that  or  c o p y i n g or  shall  not  per-  scholarly  Department  that  for f i n a n c i a l gain  The U n i v e r s i t y o f B r i t i s h V a n c o u v e r 8, Canada. Date  study.  the  in partial  d e g r e e at  the  copying of  It  this thesis  that  and  granted  representatives,,  cation  this thesis  Columbia, I agree  available  his  presenting  be  by publi-  allowed  The U n i v e r s i t y  of B r i t i s h  Columbia  FACULTY OF GRADUATE STUDIES  PROGRAMME OF THE FINAL ORAL EXAMINATION FOR THE  DEGREE OF  DOCTOR OF PHILOSOPHY  of  DONALD EVAN McALLISTER  B.A., The U n i v e r s i t y  o f B r i t i s h Columbia, 1955  M.A., The U n i v e r s i t y  o f B r i t i s h Columbia, 1957  MONDAY, JUNE 29, 1964 AT 10 A.M. IN ROOM 3332, BIOLOGICAL SCIENCES BUILDING  COMMITTEE IN CHARGE Chairman: J. R. I. P.  F. H. Soward H. D. F i s h e r W. S. Hoar P. A. L a r k i n C. C. L i n d s e y  R. Adams V. Best McT. Cowan A. Dehnel  External United  Examiner: States  S. H. Weitzman  National  Washington, D.C.  Museum  THE  EVOLUTION OF BRANCHIOSTEGAL RAYS IN TELEOSTOME FISHES ABSTRACT  The o r i g i n , f u n c t i o n and e v o l u t i o n of the b r a n c h i o s t e g a l r a y s , the r e l a t e d o p e r c u l a r and g u l a r bones and a s s o c i a t e d h y o i d elements were i n v e s t i g a t e d i n t e l e o stome f i s h e s . A l i z a r i n , s k e l e t a l or a l c o h o l i c s p e c i mens of over h a l f the l i v i n g f a m i l i e s (over 240) and a l l the l i v i n g orders of teleostome f i s h e s w i t h b r a n c h i o s t e g a l s were examined. L i t e r a t u r e p r o v i d e d data f o r most of l i n e remaining l i v i n g and f o s s i l f a m i l i e s and orders. S e v e r a l e v o l u t i o n a r y trends became apparent; a tendency f o r number of b r a n c h i b s t e g a l s t o decrease, f o l l o w ing W i l l i s t o n ' s Law; i n c r e a s i n g s e p a r a t i o n of mandibular and h y o i d a r c h e s ; and an i n c r e a s e i n number and complexity of h y o i d elements. In the development of h y o i d elements, but not of b r a n c h i o s t e g a l r a y s , the o n t o g e n e t i c sequence p a r a l l e l e d the phylogenetLc sequence. Examination of the unusual a d u l t h y o i d r e l a t i o n s h i p s i n the n e o t e n i c S c h i n d l e r i a showed i t to resemble the l a r v a l c o n d i t i o n of normal fishes. The c o n d i t i o n i n the t i n y goby, M i s t i c h t h y s , i s similar. The s t r u c t u r e of the b r a n c h i o s t e g a l s e r i e s and h y o i d elements proved v a l u a b l e i n t r a c i n g the r e l a t i o n s h i p s of f i s h e s . Major f i n d i n g s i n c l u d e : H i o d o n t i d a e were found not be be c l o s e l y r e l a t e d to the N o t o p t e r i d a e ; the N o t o p t e r i d a e and o s t e o g l o s s o i d f a m i l i e s t o be r e l a t e d t o the mormyriforms; the N e o s c o p e l i d a e and Myctophidae to d i f f e r from other myctophiforms; the o p h i d i o i d s t o r e q u i r e o r d i n a l s e p a r a t i o n from the P e r c i f o r m e s andplacement near the Gadiformes and A t e l e o p i f o r m e s ; .-the Amblyopsidae t o belong i n the P e r c o p s i f o r m e s ; the A n a b a n t o i d e i and O p h i c e p h a l o i d e i t o be c l o s e l y r e l a t e d suborders of common a n c e s t r y d e s e r v i n g placement i n the same o r d e r ; the Beloniformes to d i f f e r from most other orders i n the l o s s of the i n t e r h y a l and upper h y p o h y a l ; and the Echeneiformes to d i f f e r from most P e r c i f o r m e s i n the p o s s e s s i o n of 8-11 b r a n c h i o s t e g a l s . The number of b r a n c h i o s t e g a l s was found to be i n f l u e n c e d by p o s t e r i o r e x t e n s i o n of the jaws, small body l e n g t h , f e e d i n g h a b i t s , gill  membrane attachment and  deepsea e x i s t e n c e .  GRADUATE STUDIES Field  of Study:  Zoology  Ichthyology  J . C.  Briggs  M a r i n e Zoogeography  J . C.  Briggs  Systematics  C. C.  E v o l u t i o n a r y Mechanisms Developmental  Genetics  Lindsey  R. M. B a i l e y (Michigan) R.  R. M i l l e r (Michigan)  Other S t u d i e s : Contemporary L i t e r a t u r e P h i l o s o p h i c a l Problems  H. C. Lewis B,  Savery  PUBLICATIONS  M c A l l i s t e r , D.E. 1960. Keys t o t h e m a r i n e f i s h e s of A r c t i c Canada. N a t . Mus. Canada, N a t u r a l H i s t . Pap. 5: 1-21. M c A l l i s t e r , D.E. 1960. L e G a s t e r o s t e u s w h e a t l a n d i , n o u v e l l e espece de p o i s s o n pour l a p r o v i n c e de Quebec. L e N a t u r a l i s t e C a n a d i e n , 87(5):117-118. M c A l l i s t e r , D.E. 1961. The o r i g i n and s t a t u s of t h e deepwater s c u l p i n , Myoxocephalus t h o m p s o n i i , a n e a r c t i c g l a c i a l r e l i c t . N a t . Mus. Canada, B u l l . 172: 44-65. M c A l l i s t e r , D.E. and C C . L i n d s e y . 1961. S y s t e m a t i c s of t h e f r e s h w a t e r s c u l p i n s ( C o t t u s ) of B r i t i s h Columbia. N a t . Mus. Canada, B u l l . 172: 66-89. M c A l l i s t e r , D.E. 1962. F i s h remains from O n t a r i o I n d i a n S i t e s 700 t o 2500 y e a r s o l d . N a t . Mus. Canada, N a t u r a l H i s t . Pap. 17: 2-6. M c A l l i s t e r , D.E. 1963. f a m i l y , Osmeridae. 191: 1-53.  A r e v i s i o n of t h e smelt N a t . Mus. Canada, B u l l .  THE EVOLUTION OF BRANCHIOSTEGAL RAYS IN TELEOSTOME FISHES ABSTRACT The origin, function and evolution of the branchiostegal rays, the related opercular and gular bones and associated hyoid elements were investigated in teleostome fishes.  Alizarin, skeletal or alcoholic  specimens of over half the l i v i n g families (over 2/+0) and a l l the living orders of teleostome.fishes with branchiostegals were examined. Literature provided data for most of the remaining l i v i n g and f o s s i l families and orders. Several evolutionary trends became apparent; a tendency for number of branchiostegals to decrease, following WiHiston s Law; increasing f  separation of mandibular and hyoid arches; and an increase i n number and complexity of hyoid elements. In the development of hyoid elements, but not of branchiostegal rays, the ontogenetic sequence paralleled the phylogenetic sequence. Examination of the unusual adult hyoid relationships i n the neotenic Schindleria showed i t to resemble the larval condition of normal fishes. The condition i n the tiny goby, Mistichthys, i s similar. The structure of the branchiostegal series and hyoid elements proved valuable i n tracing the relationships of fishes. include:  Major findings  Hiodontidae were found not to be closely related to the  Motopteridae; the Notopteridae and osteoglossoid families to be related to the mormyriforms; the Neoscopelidae and Myctophidae to differ from other myctophiforms; the ophidioids to require ordinal separation from the Perciformes and placement near the Gadiformes and Ateleopiformes; the Amblyopsidae to belong in the Percopsiformes; the Anabantoidei and  iii Ophicephaloidei to be c l o s e l y related suborders of common ancestry deserving placement i n the same order; the Beloniformes to d i f f e r from most other orders i n the l o s s of the interhyal and upper hypohyal; and the Echeneiformes to d i f f e r from most Perciformes i n the possession of 8-11  branchiostegals.  The number of branchiostegals was found to  be influenced by posterior extension of the jaws, small body length, feeding habits, g i l l membrane attachment and deepsea existence.  iv NEW TAXA  Hiodontoidei, new suborder  P» 151  Ichthyotringidae, new name  p. 197  Barbourisioidei, new suborder  p. 202  Gymnarchoidea, new superfamily.... p. 224 Ophidiiformes, new o r d e r . . . .  p. 311  V  TABLE OF CONTENTS INTRODUCTION  p. 1  Literature Definitions Classification  p. 3 p. 4 p. 11  METHODS  p. 11  EMBRYOLOGY  p. 13  FUNCTION  p. 16  Respiration Feeding Behavior Protection of G i l l s Defense THE ORIGIN OF THE BRANCHIOSTEGAL SERIES The The The The  branchiostegals operculum and suboperculum interoperculum gular plates  p» 17 p. 18 p. 19 p. 21 p. 21 p. 23 p. p. p. p.  23 26 27 28  PHYLOGENETIC OR VERTICAL EVOLUTION  p. 31  CLASS TELEOSTOMI  p. 32  Key Key Key Key Key  to to to to to  the the the the the  classes of Gnathostomata subclasses of Teleostomi orders of Crossopterygii orders of Dipneusti orders of Actinopterygii  SUBCLASS CROSSOPTERYGII /Order Hoploptychiformes /Order Osteolepifonnes Order Coelacanthiformes SUBCLASS DIPNEUSTI /Order /Order /Order /Order  Dipteriformes Phaneropleuriformes Uronemiformes Ctenodontiformes  p. p. p. p. - p.  33 34 34 35 36  p. 41 p. 41 p, 43 p. 48 p. 53 p. p. p. p.  55 58 60 61  vi SUBCLASS DIPMEUSTI  (Cont'd) P» 63 P» 64  Order Ceratodiformes Order Lepidosireniformes SUBCLASS BRACHIOPTERYGII  P« ? 6  Order Polypteriformes  P» 67  SUBCLASS ACTINOPTERYGII GROUP I. /Order /Order /Order /Order /Order /Order /Order /Order /Order /Order /Order /Order /Order /Order /Order /Order /Order /Order Order GROUP II. /Order Order Order /Order /Order /Order GROUP I I I .  P«  6  9  CHONDROSTEI  P'  7  1  Palaeonisciformes Tarrasiiformes Phanerorhynchiformes Haplolepiformes Redfieldiiformes Perleidiformes Dorypteriformes Bobasatraniifonnes Pycnodontifornies Ptycholepiformes Pholidopleuriformes Cephaloxenifoi-mes Aethodontiformes Luganoiiformes Peltopleuriformes Platysiagiformes Chondrosteiformes Saurichthyiformes Acipenseriformes  P* 71 P" P* ^* f P. 83 P» 85 P* 87 P» P* 9 P» 91 P» 92 P» 94 P* 95 P» 96 p« 96 P» 98 P« 99 P» 1^1 P» l ^  HOLOSTEI Ospiiformes Amiiformes "Lepisosteiform.es Aspidorhynchiformes Pachycormiforraes Pholidophoriformes TELEOSTEI  MALACOPTERYGII  Order Order Order Order Order  Clupeiformes Myctophifomies Motacanthiformes Giganturiformes Saccopharyngiformes  7  9  8  0  8  8  8  ,  2  P»  1 0  6a  P» l°6a ' P» ^ 9 P* -L19 P* P -*-3 P* ^-4 #  2  2  P*  1  P"  1  2  8  2  8  P« 1 9 P» 184 P* ^6 P» ^ P« 14 2  2  2  2  2  vii SUBCLASS ACTINOPTERYGII . (Cont»d) Order Order Order Order  Mormyriformes Cyprinif onnes Anguillifonnes Beloniformes  P« P« P» P»  ACANTHOPTERYGII Order Berycifonnes Order Lampridifonnes Order Zeiformes Order Bathyclupeiformes Order Syngnathifonnes Order Ophidiiformes Order Ateleopifonnes . Order Gadifonnes Order Percopsiformes Order Cyprinodontifonnes Order Pleuronectiformes Order Perciformes Order Gasterosteifonnes Order Icosteiformes Order Echeneiformes Order Tetraodontifonnes Order Mastacembeliformes Order Synbranchiformes Order Lophiiformes Order Batrachoidifonnes Order Gobiesocifonnes Order Pegasifonnes  216 226 251 273  P- 280 P» 281 P» 291 P» 296 P» 301 p. 303 P» 311 P» 319 P» 322 P« 329 P» 335 P« 340 p. 346 P» 373 p. 376 P» 378 P* 381 P» 389 P» 393 P» 395 p. 407 P« 408 P» 413  DISCUSSION OF RESULTS  P» 417  ADAPTIVE EVOLUTION  P« 422  Accessory respirator;' organs F i l t e r feeding apparatus Size Jaw length G i l l membrane attachment Deep sea -  P» P» P« P« P» P»  422 ^2° 427 431 433 434  SUMMARY AND CONCLUSIONS  p. 436  LITERATURE CITED  p. 439  viii LIST OF TABLES Table 1. Summary of data oh branchiostegal series and hyoid arch in teleostome fishes (page 419). Table 2 . Relation between aerial respiratory organs and branchiostegal number and g i l l membranes (page 424). Table 3. Number of branchiostegals and g i l l membrane attachment in some giant fishes (ten feet or longer) (page 428). Table 4. Branchiostegal number and g i l l membrane attachment in miniature fish (groups having many species of three or less inches) (page 429).  ILLUSTRATIONS  Fig. 1.  General features and relative positions of branchiostegals, operculars, gulars, hyoid arch and g i l l membranes. (Follows page 4)*  Fig. 2.  Percopsid projections (arrow) in a percopsiform, gadiform and ophidiiform (top to bottom).  F i g . 3»  (Follows page 3 H ) .  Opercular spines in Anabas and Holocentrus.  Note the  similarity, although the suboperculum of Holocentrus differs in occluding the posterior border of the operculum. (Follows page 356). The following plates at end of thesis. P l . I.  Branchiostegal series in the Crossopterygii.  P l . II.  Branchiostegal series in the Dipnoi.  P l . III.  Branchiostegal series in the Actinopterygii (chondrostei).  P l . IV.  Branchiostegal series in the Actinopterygii (Chondrostei and Holostei) and Brachiopterygii.  P l . V.  Branchiostegal series in the Actinopterygii (Chondrostei and Holostei).  P l . VI.  Branchiostegal series and hyoid arch in the Actinopterygii (Mai acopterygii ) •  P l . VII.  Branchiostegal series and hyoid arch in the Actinopterjrgii (Holostei and Teleostei).  (In these and the following  photographic plates retouching was used to improve definition). PI. VIII.  Branchiostegal series and hyoid arch in the Actinopterygii (Maiacopterygii).  PI. IX.  Branchiostegal series and hyoid arch in the Actinopterygii (Maiacopterygii).  PI. X.  Branchiostegal series and hyoid arch in the Actinopterygii (Malacopterygii and Acanthopterygii).  PI. XI.  Branchiostegal series and hyoid arch in the Actinopterygii (Acanthopterygii).  PI. XII.  Branchiostegal series and hyoid arch in the Actinopterygii (Ac anthopterygii)•  PI. XIII.  Branchiostegal series and hyoid arch in the Actinopterygii (Acanthopterygii).  PI. XIV.  Branchiostegal series and hyoid arch in the Actinopterygii (Acanthopterygii).  PI. XV.  Branchiostegal series and hyoid arch in the Actinopterygii (Acanthopterygii).  PI. XVI.  Branchiostegal series and hyoid arch in the Actinopterygii (Acanthopterygii).  P l . XVII.  Branchiostegal series and hyoid arch in the Actinopterygii (Ac anthopterygii).  P l . XVIII.  Evolutionary relationships of the teleostome fishes. Based on the study of the branchiostegal series and hyoid arch and on other characters.  ACKNOWLEDGEMENTS My deepest gratitude is due Dr. J . C. Briggs under whom this study began and Dr. R. H. Rosenblatt under whom the final drafts were written. Drs. N. J . Wilimovsky, C. C. Lindsey, V. J . Krajina, P. A. Dehnel and P. A. Larkin also criticized the manuscript. Many generous people donated, loaned or exchanged rare groups of fishes, greatly adding to the scope of the study.  These include Dr. W.  Aron, then at the University of Washington, Dr. R. M. Bailey of the University of Michigan, Mr. G. Bell-Cross of the Northern Rhodesia Department of Game and Fisheries, Dr. E . J . Crossman of Royal Ontario Museum, Dr. W. A. Gosline of the University of Hawaii, Mr. R. Kanazawa of U.S. National Museum, Mr. E . D. Lane then of the Fisheries Laboratory, Wellington, New Zealand, Dr. A. G. K. Menon of the Zoological Survey of India, Dr. G. S. Myers of Stanford University, Dr. R. H. Rosenblatt of Scripps Institution of Oceanography, Dr. L . P. Schultz of U.S. National Museum, Dr. W. B. Scott of Royal Ontario Museum, Dr. F . H. Talbot of the South African Museum, Dr. W. Templeman of the Biological Station, St. John's, Newfoundland, Dr. J . Thiemmeda of Uasetsart University, Thailand, Dr. A. D. Welander of the University of Washington, Mr. P. J . Whitehead of the British Museum (Natural History). Miss Audrey Dawe, librarian of the National Museum of Canada, was untiring in seeking out rare journals.  Mr. 5. Gorham of the National  Museum of Canada prepared a series of excellent skeletons. The author is grateful to Dr. L . S . Russell and Dr. A. W. F . Banfield for their continued support of this project. To a l l these persons the author extends his most sincere thanks.  INTRODUCTION This i s a study of the evolution of branchiostegals in teleostome fishes.  The study considers the vertical evolution of branchiostegals  with special regard to ordinal phylogeny of teleostome fishes.  It also  considers the horizontal evolution of branchiostegals in regard to the effect of internal and environmental factors.  The homologous structures,  the opercular bones and gular plates, and the elements of the hyoid arch (except the hyomandibular, urohyal, and the glossohyal)"*" upon \\rhich the branchiostegals insert, are also studied, although in less detail.  The  origin, development, and function of the branchiostegals are also dealt with.  The central problem considered is to what extent the branchiostegals  reflect the phylogeny of the teleostome fishes. Lh the evolution of a group, a morphological structure has three courses.  It may remain the same or almost the same.  even i f other structures are evolving rapidly.  It may do this  Secondly, i t may advance  through modification of form, through complication or addition. i t may degenerate through simplication, loss or disappearance. these courses are of value to the student of phylogeny.  Thirdly, A l l of  Possession of a  structure nearly similar by two groups, supposing the similarity is not due to parallelism, suggests relationship and common origin.  Differences  wrought through evolutionary change towards complexity or simplicity suggest placement in different phylogenetic lines or in different taxa, the closeness of relationship depending on the degree of difference. Through this method a sequence of relationships may be built up, and  These bones can be important systematically but are not directly associated with the branchiostegals.  2  through examination of fossils and determination of primitive characters the sequences can be transformed into a phylogenetic tree or dendrogram. A clear picture of phylogeny cannot be gained through examination of a single character.  Because of parallel evolution and because of  different rates of evolution in different structures a single character may lead one astray in tracing phylogeny.  A clear picture of phylogeny  i s based on as many firm taxonomic characters as possible.  This reduces  the probability of confusing homologous and analagous characters and presents a picture of the evolution of the whole animal and not just one port.  Therefore, in this study the relationships suggested by the  branchiostegal series (operculars, branchiostegals, gulars) and the hyoid arch, are checked with other sound taxonomic characters (from literature or original observations). The concentration which the study of a single characters complex enables has advantages over the studying of many characters simultaneously.  Parallelisms are more readily noted.  are less l i k e l y to be ignored. studies may be noted:  Smaller differences  Some valuable single character complex  Hubbs (1920) on the branchiostegals, Starks (1930)  on the bones of the shoulder girdle and (1926) on the ethmoid bones, Burne (1909) and Derscheid (1924) on the olfactory organ, Whitehouse (1910) and Gosline (i960), (1961) on the caudal skeleton, Emelianov (1935) on the ribs, Frost (1925), (1926), (1927), etc.  on the otloliths,  Stensio (1947) on the sensory canals of the head, Lindsey (1956) on the vertical fins.  Holstvoogd (1963) on the retractores arcuum branchialium  3 and Freihofer on the ramus lateralis accessorius.^  None of these  studies ha3 included a l l the orders and only one more than 100 families. It i s from the combination of detailed studies such as these and others yet to be done that the ultimate picture of the phylogeny of the Teleostomi w i l l be constructed.  Towards this end the present paper  hopes to contribute. Literature Branchiostegal counts have been used in fish taxonomy even before the time of Linnaeus.  The more careful ichthyologists such as Day,  Regan, Smitt and Jordan have included branchiostegals in their descriptions and analyses of fishes, as have G i l l , Ryder and Starks in their osteological  studies.  There have been few studies of branchiostegals on the broad scale however.  Bertelsen and Marshall (1956) discuss the number and  arrangement of branchiostegals in some of the malacopterygian orders while placing the Miripinnati.  The only other study, and the most  important one, i s that of Hubbs (1920).  This concise study enumerates  many of the important evolutionary changes in the branchiostegals of living fishes.  Hubbs noted the tendency for decrease in branchiostegals  during evolution (noted previously as early as 1904), and the differences in shape and arrangement of the branchiostegals of malacopterygians and acanthopterygians.  He noted the malacopterygian nature of the  branchiostegals in the Synentognathi, and the acanthopterygian nature of the branchiostegals in the Microcyprini, Symbranchia and Opisthomi. Two further valuable studies in progress may be noted, that of Quentin Bone, Marine Laboratory, Plymouth on lateral muscle innervation and G. Nelson, University of Hawaii on the branchialarches.  4 He based his conclusions on the examination of about 140 families distributed in less than twenty orders, but gave no figures, and described only a few in detail. The hyoid arch, aside from papers on the osteology of single species, has received little.attention from the broad comparative point of view in fishes.  Corsy (1933) studied the evolution of the hyoid  arch of vertebrates but only a small portion of this study was devoted to teleostome fishes.  Khanna (1961) described the hyobranchial  skeleton of some Indian fishes.  A U i s (1915) and (1928) and Edgeworth  (1926) and (1931) comment on the lox\rer elements in discussions upon the homologies of the hyomandibular. This paper tries to extend these and other comparative studies by the inclusion of fossil groups, the examination of every order of fishes with branchiostegals and as many families as possible (over half of the .  (  living families),"'" the presentation of data i n a consistent style, the illustration of many forms, and in the interpretation of the data in terms of phylogeny, adaption and parallelism. Definitions To introduce the subject and to clarify the terminology, the technical terms pertinent to the study are here defined, synonyms listed and structures are illustrated (fig. l ) . 1  The terminology of Harrington  ' — — — — — Over 240 of the 402 l i v i n g families and over 330 species and 700 specimens examined. Counts lacking on only 16 l i v i n g and 42 f o s s i l families ( i . e . data (own & literature) available for 452 of total of 510 l i v i n g and f o s s i l teleostom.3 families). A l l l i v i n g orders with branchiostegals were examined.  5  (1955) is used, as far as i t applies. the older synonyms.  Starks (1901) may be referred to for  Two terms, spathiform and acinaciform are  introduced for the f i r s t time. Branchiostegals or branchiostegal rays;  These are the struts of  dermal bone (sometimes cartilage) below the operculars, that insert on the hyoid arch and support the g i l l membrane of Teleostomi.  The term  lateral gulars i s sometimes misapplied to the broad branchiostegals of Chondrostei.  The branchiostegals are here believed to be homologous  with the hyoid rays of Acanthodii and ELasraobranchii (fused into the "opercular plate" of chimaeras). Branchioperculum:  This is the enlarged uppermost branchiostegal  in Amia. Jugostegelia:  These are the branchiostegals free from the hyoid  arch and overlapping, found in the anguilliform families, Echelidae, Ophichthidae and Neenchelyidae. Spathiform:  Applies to the broad, laminar, paddle-shaped  branchiostegals found in some malacopterygian and most of the more primitive teleostomes.  From the Latin spatha or spatula.  E.g.  branchiostegals of Amia. Acinaciform:  Applies to the slender, non-laminar, sword or  scimitar-like branchiostegals found in some malacopterygians and most actinopterygians.  From the Latin acinaces or scimitar. E . g .  branchiostegals of Perca. Operculum:  The large dermal bony (sometimes cartilaginous) upper  element of the g i l l cover behind the preoperculum and inserting on the hyomandibular in teleostomes.  Believed to be an enlarged branchiostegal.  Ventral View GEKERAL VICt£ CP BRANCH 06 TEGALS (ID Amia calva)  BRANCH!OSTEGAL AND HTOID ARCH TERMINOLOGY  G U I Membranes Separate G i l l Membranes United G i l l Membranes Joined G i l l Membranes Joined and Free From Isthmus to Isthmus - Narrowly to Isthmus - Broadly  G i l l Opening Restricted  G i l l Membrane Joined to Isthmus and Forming a Free Fold Over I t  GILL MEMBRANE ATTACHMENT  Fig. 1.  General features and relative positions of branchiostegals, operculars, gulars, hyoid arch and g i l l membranes.  7 Suboperculum;  The large, dermal, bony (sometimes cartilaginous)  g i l l cover element below the operculum in teleostomes.  Believed to be  an enlarged branchiostegal. Interoperculum;  The large, dermal, bony (sometimes cartilaginous)  element below the lower arm of the preoperculum and anterior to or under the front half of the suboperculum.  It typically is connected to the  mandible, epihyal and suboperculum.  Believed here to be an enlarged  branchiostegal. Operculars;  Found only in higher teleostomes (Group II and above). Collective terra for the operculum, suboperculum and,  i f present, the interoperculum. G i l l membrane or branchiostegal membrane:  The membrane lying  between the operculars and the isthmus which is supported by the branchiostegals. isthmus.  The g i l l membranes may be variously connected to the  If the g i l l membranes are not connected to one another or the  isthmus and overlap anteriorly they are termed separate (e.g. Salmo, Sphyraena).  If the g i l l membranes are attached to one another, yet not  joined to the isthmus (at least posteriorly), then they are said to be united and free from the isthmus (e.g. Polyodontidae, Notopteridae); they may in this case have a small or large free border posteriorly (whether the posterior edge i s free may be determined by running a needle under i t ) .  In the Synbranchifonnes the g i l l openings are united  and free from the isthmus but dorsally attached to the body before the pectoral f i n ; this gives the appearance of a single ventral g i l l opening but is really only a special case of being united and free.  Lastly, the  g i l l membranes may be joined to the isthmus (e.g. most Cyprinidae, Gobiidae).  They may be narrowly joined to the isthmus (e.g.  Gasterosteus)  8  or joined to the isthmus anteriorly in which case the g i l l opening i 3 wide, or they may be broadly joined to the isthmus (e.g. most Cyprinidae) in which case the g i l l opening is narrow and the space between the g i l l openings is wide, or the g i l l opening may be restricted (e.g. Anguillidae) in which case the g i l l opening is reduced to a small aperture on the side of the head.  When the g i l l membranes are joined  to the isthmus a fold may form across the isthmus between the g i l l s l i t s (e.g. Myoxocephalus polyacanthocephalus) which secondarily resembles the g i l l membranes united and free condition.  The preceding terms have not  been used consistently by some authors but the definitions and illustrations given here should make the distinctions clear and should help standarize the terminology. Median gular;  A median bony plate extending backwards from the  symphysis between the mandibles.  It i s bordered posteriorly by the  lateral gulars or branchiostegals, i f present. v-shaped pit l i n e . Amia Elops. f  Primitively i t bears a  It may be homologous with the branchiostegals.  E.g.  A second median gular, posterior to the normal median  gular i s found in some Dipneusti. Lateral gulars;  Pair(s) of bony plates, larger than the  branchiostegals, lying between the median gular and branchiostegals (when present), and inserting on the hyoid arch medial to the mandibles. It is believed here to be homologous with the branchiostegals. Primitively bears a transverse pit l i n e . Latimeria.  E . g . Polypterus, Calamoichthys,  In some Dipneusti there may be two pairs, an anterior and a  posterior pair.  9  Gulars:  Collective term for median and lateral gulars.  Branchiostegal series:  Collective term for the operculars,  branchiostegals and gulars ( a l l branchiostegal derivatives). Interhyal:  Endochondral bony or cartilaginous, usually cylindrical  element in teleostomes connecting the lower portion of the hyoid arch to the hyomandibular.  It acts as a pivot.  It may or may not be  homologous \-rith the tetrapod stylohyal, which term has been used for i t . The interhyal typically inserts on the lower tip of the hyomandibular. Paired. Epihyal:  Endochondral bony or cartilaginous usually triangular  element in higher teleostomes (Group II and III) lying between the ceratohyal and interhyal. Ceratohyal:  Probably derived from the ceratohyal.  Paired.  Endochondral bony or cartilaginous usually hourglass-  shaped element in teleostomes lying between the epihyal, i f present, or interhyal and the hypohyal(s).  Paired.  Found in Acanthodii,  Elasmobranchii and Teleostomi. Kypohyal(s):  Endochondral bony or cartilaginous element(s) lying  below the ceratohyal and lateral to the glossohyal, in Acanthodii and Teleostomi.  In the Crossopterygii, Dipneusti and lower Actinopterygii  (Group IIB and lower) the hypohyal i s single; in the higher Actinopterygii (except where secondarily degenerate) there is a lower (hypohyal l ) and an upper (hypohyal 2) hypohyal.  Called basihyals by  some authors. Hyoid arch:  Restricted in this study to include only the interhyal,  epihyal, certaohyal and hypohyals (since the other hyoid elements, the hyomandibular and basihyal (= glossohyal) were not included in this studjO.  10 Sutured:  The epihyal and ceratohyal are termed sutured i f they  are joined by interdigitating prongs emitted by each bone, while they are termed separate i f not so joined. Clupeoid projection:  This is a bulge on the anterior edge of the  base of branchiostegals in clupeoids and their derivatives.  Percopsoid  projection i s an angulation on the anterior branchiostegal base (see f i g . 3). Beryciform foramen:  This is a perforation above the midsection of  the centre of the ceratohyal found in beryciform fishes and some of their derivatives.  In some fishes the roof of the foramen is lost and  only a notch appears on the dorsal edge of the ceratohyal.  The foramen  perforates the groove along which the hyoid artery runs on the outer face of the ceratohyal. Positional terms:  Since the hyoid arch may be almost horizontal  or almost vertical the branchiostegals towards the interhyal end of the arch may either be called dorsal or posterior branchiostegals.  The  branchiostegals toward the hypohyal end of the arch may similarly be called ventral or anterior branchiostegals.  In numbering the  branchiostegals the uppermost (or posteriormost) provided the starting point since the lower (anterior) branchiostegals are the most variable and do not provide as stable a point of enumeration.  The portion of  the branchiostegal inserting on the hyoid arch is termed basal, the opposite end the distal t i p .  The two long edges may be called the  ventral (anterior) edge and the dorsal (posterior) edge.  According to  their insertion branchiostegals are divided into epihyal and ceratohyal  11  (sometimes interhyal and hypohyal), external and ventral or internal branchiostegals.  When a branchiostegal straddles the epihyal-ceratohyal  or a ceratohyal-hypohyal joint a half a branchiostegal is awarded to each (recorded in descriptions and tables as 2 ) . Classification The basis of the classification used herein is that of Berg (1947; 1955)*  Modifications of this classification were made from the later  literature.  Changes, sometimes considerable, were also made in the  classification of l i v i n g fishes, mainly in the rearrangement of orders and status of certain groups, as suggested by this study and data from other studies.  The uniform -iformes ending was adopted for orders,  -oidei for suborders, -idae for families and -inea for subfamilies. METHODS The branchiostegal series and hyoid bones were examined by several methods.  The principal method was by clearing and staining xvith alizarin  following the method of Hollister (1934). Specimens preserved in alcohol usually from three to six inches but sometimes a3 short as one inch (Phallostethidae) or as long as sixteen inches were employed for staining.  The stained hyoid arch with the branchiostegals was usually  removed and examined. microscope.  Some were photographed under a binocular  In quite a few cases dermestid-cleaned skeletons were  examined; here caution must be employed since branchiostegals may be lost during skeletonizing.  Alcoholic specimens were dissected for  examination of the arch and branchiostegals.  From other alcoholic  specimens branchiostegal counts were taken without dissection.  In the  12 latter method one mu3t check to see i f the uppermost branchiostegal is hidden under the suboperculum or whether the lowest branchiostegal, which may be quite small, is not obscured by the skin.  An attempt was  made to examine at least one specimen from as many families as possible. Representatives were chosen by availability except that as many families and suborders as possible were examined. Branchiostegals were counted on the l e f t .  When the branchiostegals  were abnormal (see Crossman, I960, for examples) the counts were not recorded.  E . g . fused, bent, or irregularly placed branchiostegals.  For families not examined and to supplement families examined, counts were obtained from the literature. wholly obtained from the literature. References under the family. parentheses.  Information on fossils was  These sources are included in  Synonyms of taxa follow enclosed in  Fossil groups are indicated by the sign  Observations were made at the Vancouver Public Aquarium to gain an understanding of the movements of the elements in a living f i s h . The principal sources of material were the National Museum of Canada, Ottawa (NMC), and the museum of the Institute of Fisheries, Universitj' of British Columbia (BC). Other material was borrowed from Stanford University (SU), and Roj^al Ontario Museum (ROM), British Museum (BM), Scripps Institution of Oceanography (SIO), and University of Michigan Museum of Zoology (UMMZ), or examined at the United States National Museum (USNI-l). Acknowledgements note other sources.  13 EMBRYOLOGY The hyoid arch develops from the second visceral arch, the f i r s t becoming the jaws, the more posterior ones supporting  g i l l 3 .  The  following, from de Beer (1937)* Wade (1962) and original observations on Amia appear to be the usual order of development:  l ) ventral  extension of a cartilaginous hyomandibular-symplectic rod from the auditory capsule and appearance of a ceratohyal cartilage below this, 2) separation of the hyomandibular-symplectic cartilage from the auditory capsule, 3) appearance of the interhyal half or three quarters of the way up the lower side of the hyomandibular-symplectic cartilage and appearance of a hypohyal, /+) appearance of the upper, then the lower branchiostegals, appearance of the median gular, operculum, suboperculum and interoperculum, 5) ossification of the ceratohyal in the anterior and epihyal in the posterior end of the ceratohyal cartilage, and of the symplectic and the hyomandibular in their cartilage, 6) ossification of the upper and lower hypohyal in the hypohyal cartilage, 7) suturing of epihyal and ceratohyal (delayed t i l l adult in Anarhichas).  In different  groups the exact sequence may vary and of course not a l l of these elements are found in a l l teleostomes. It is interesting to compare the ontogenetic and phylogenetic appearance of the hyoid elements.  This is done below:  Ontogeny  Phylogeny  l)  ceratohyal cartilage  hypohyal and ceratohyal  2)  a hypohyal and interhyal cartilage  interhyal  3)  epihyal and ceratohyal ossification  epihyal  14 4)  upper and lower hypohyal ossification  upper and lower hypohyal  5)  suturing of epihyal and ceratohyal  suturing of epihyal and ceratohyal  In comparing the sequence of appearance of the hyoid elements in the table above i t may be seen that the embryonic sequence of appearance of every element follows the phylogenetic sequence of origin in every case except that of the hypohyal which i s delayed to the next stage in embryonic development. The embryonic development of the hyoid arch is also valuable because i t suggests the two hypohyals develop from a single precursor, the cartilaginous hypohyal, a point which the positional relationships of the two adult hypohyals would tend to confirm.  The embryonic  development of the epihyal from the ceratohyal would also appear to be a morphologically and phylogenetically plausable development. The development of the branchiostegals does not appear to recapitulate phylogeny.  In the higher teleosts numerous branchiostegals  do not appear and then secondarily diminish to a reduced number, perhaps because of selection at the embryonic stage.  Nor do the embryonic  branchiostegals of higher teleosts commence embryonically as spathiform and then change to acinaciform shape:  instead, they commence as  acinaciform. Embryology enables one to explain one of the unusual characters of the Schindlerioidei,  Gosline (1959) states the Schindlerliidae were,  as far as he knew, unique in having the epihyal inserting on the upper head of the hyomandibular. However, as noted above, the interhyal  15  commonly inserts high up on the lower side of the hyomandibularsymplectic cartilage embryonically; the point at which i t inserts marks the later point of division of the lower end of the hyomandibular and the upper end of the symplectic.  Development in the neotenic Schindleria  appears to have, ceased at a point before the cartilage differentiated into the hyomandibular and symplectic; the epihyal therefore appears to insert on the upper head of the "hyomandibular" (= hyomandibularsymplectic cartilage).  Thus, the position of the hyoid arch and  "hyomandibular" is unique only that i t i s found in the adult, and this is not surprising since one expects to find larval conditions in a neotenic f i s h .  An unusual condition is that a hypohyal is not present,  although the epihyal has made i t s appearance.  A similar condition is  found in the minute goby, Mystichthys luzonensis where the interhyal inserts above the ventral end of the hyomandibular. Another unusual condition that embryology elucidates i s the origin of the mental barbels in the Mullidae.  Here there are only 3 normal  branchiostegals on the external face of the hyoid arch.  At the  anteriormost end of the ceratohyal close to the symphysis in the adult is a slightly twisted osseous ray which becomes attenuate and cartilaginous distally. branchiostegal (Starks,  This ray has been suggested to be a 1 9 0 4 ) ,  thus accounting for the missing fourth  branchiostegal one expects on the external face of the hyoid arch. Bianco  (190?)  and Caldwell  (1962)  Lo  investigated the development of mullids.  At 6 - 8 mm. 4 slender branchiostegals were found in the normal position, at 1 1 - 1 5 ram. the fourth branchiostegal thickened, at 2 2 inm. the branchiostegal began moving anteriorly and medially, to achieve at 3 0 mm.  16 nearly the adult mental condition.  Here the study of development  confirms the theory that the mental hyoid ray i s indeed a branchiostegal. I t would be i n t e r e s t i n g to follow the development of Polymixia,  an  unrelated form which has a hyoid barbel believed to be supported by branchiostegals.  Another worthy problem would be the close following  of the development of the median gular to compare i t with  branchiostegals  development for evidence on whether or not they are homologous. A series of young Amia calva were examined from two collections length;  (NMC53-192-3, Pt.  NMC58-209, Georgian  Pelee, Lake E r i e ,  Bay, Lake Huron,  Ontario  20.6-26.7  44.5-50.1  mm.  mm.  standard  length).  The following r e l a t i o n s h i p between standard length and number of branchiostegals was  found:  Standard Length (mm.) No. Branchiostegals  21  23  5  7  25 . 2 6 7-8  8-9  27 9  These data would suggest that by 46 mm. of 10-13  branchiostegals i s attained.  attained the adult number of  44  46  47  48  49  8-13  12  13  12  12  50 10-12  standard length the adult number Gasterosteus  6 (Runyan, 1961);  at 25 mm.  Neostethus of  attained the adult complement of 5 (own observation).  have  25 mm.  had  I t would seem  advisable not to take branchiostegal counts as representative of the adult condition from very young specimens. FUNCTION OF TIDS BRANCHIOSTEGAL SERIES The bones of the branchiostegal series may  function i n f i v e ways,  i n r e s p i r a t i o n , i n feeding, i n sensing, i n protection of the g i l l s i n protection or defense of the f i s h .  and  These functions are discussed below.  17  Respiration Respiration in teleosts is accomplished by maintaining an almost continuous flow of water over the g i l l filaments.  The buccal cavity  creates a positive pressure before the g i l l s and the operculum and branchiostegals create a negative pressure behind the g i l l s . is summarized (from Hughes and Shelton, 1958) in four phases:  The cycle l ) Water  is drawn into the mouth past the open buccal valves by negative pressure created by.dropping the lower jaw, which then starts to close.  As this  happens the operculum is abducting \n.th the opercular cavity closed by the branchiostegal membrane (opercular valve), thus creating a negative pressure and drawing water through the g i l l s from the buccal cavity. 2) As the mouth closes the buccal cavity is reduced; water leaves the mouth until the buccal valves close, causing a rise in pressure.  As  this happens pressure in the opercular cavity i s less negative because of flow through the g i l l s .  A3 the operculum reaches the end of i t s  abduction the pressure within the opercular cavity equals the external pressure and the branchiostegal membrane opens.  3) The operculum begins  to abduct with a gap between i t and the flank, through which water exits. The mouth closes increasing buccal cavity pressure, forcing \tfater over the g i l l s with l i t t l e loss out the mouth as the l i p s are close and the buccal valves effective,  k) The mouth begins to open increasing the  volume of the buccal cavity and opening the buccal valves, and dropping the pressure in the buccal cavity.  The operculum continues to abduct  raising the opercular cavity pressure as the gap between the operculum and flank decreases.  At this point there i s a tendency for reversal of  18  water flow across the g i l l s .  From this resume i t may be seen that the  branchiostegal membrane functions as a valve to seal the g i l l opening during abduction of the operculum.  Secondly, i t acts as an expansable  wall (comparable to the rib cage) which permits the volume of the opercular cavity to enlarge and allo>?s a grea.ter volume of water to be drawn through the g i l l s .  This is accomplished by spreading the  branchiostegals (much like unfolding a fan). Intermittently the branchiostegals take part in a coughing reflex. Mere water flow is reversed through the g i l l s to clean them of debris. It is possible that branchiostegals function also in aerial respiration.  Under conditions of low oxygen, surface dwelling  physostomous fishes may inhale air bubbles.  It i s possible that  abduction of the branchiostegals may assist in this process.  It is  notable that the branchiostegals of surface dwelling physostomous fish are broad imbricating structures while those of deepwater or physoclistous fish are slender and non-imbricating. It is possible that reflexing the spathiform branchiostegals assists in inhaling bubbles of a i r . Depression of gular bones may assist in inhaling air also. Feeding Many fish feed by inhaling the food particles into the mouth.  In  macrophagus fish this probably takes place mainly by dropping the floor of the buccal cavity, although the creation of negative pressure in the opercular cavity by the operculum and branchiostegal membrane may take some part in this.  It is in the microphagus or plankton feeders that  these latter actions are more important.  Here water is drawn through  19 the sieving apparatus of the g i l l s , the g i l l rakers and out the long gill slit.  A long g i l l membrane with numerous, branchiostegals is  necessary to open and close the long g i l l s l i t during feeding and respiration. Curry-Lindahl (1956) reports that the lungfish, Protopterus, sucks i t s food into the mouth.  He quotes an author saying this is accomplished  by depression of the hyoid bone.  It may be that this behavior is a  holdover from ancestors which had gular plates.  Gulars would help in  sudden depression of mouth floor and hence sucking in of prey. Behavior The branchiostegals and their membranes have been shown to play a part in behavior of fishes by modern ethologists.  The branchiostegal  membranes are commonly employed in agonistic displays by fishes. the branchiostegals are spread and thrust laterally.  Here  For example in  cichlids, "fighting begins with lateral display in which the fishes, in breeding colors, hold themselves parallel to each other, with the median fins and eventually the branchiostegal membranes erected". 1957).  (Baerends,  This aggressive component, raising the branchiostegals, may be  employed in t e r r i t o r i a l behavior, in establishing social hierarchies (Allee, 1952) and in courtship (Morris, 1954).  It may be noted that the  erecting of the operculum and branchiostegal membrane has the effect of enlarging the head.  This type of display is known in such fishes as  Gasterosteidae, Cottidae, Cichlidae, and Anabantidae. Another behavioral function of the branchiostegal membrane can be suggested, although not yet proven.  Differences exist in coloration of  2 0  related forms.  Red slashes occur in the hyoid cleft on the lower side  of the head i n Salmo c l a r k i i . light colored.  In other species of Salmo this cleft is  In Thymallus arcticus on the other hand i t i 3 black.  In other groups there are differences in photophore pattern on the branchiostegal membrane. .In Porichthys species may have U-shaped or V-shaped patterns of photophores (Hubbs and Schultz, 1939).  Differences  in the number of photophores on the branchiostegals of sternoptychids are given by Schultz (1961): 3.  Argyropelecus and Polyipnus 6, Sternoptyx  It i s possible that the role of color i s important only in agonistic  behavior.  However, the fact that the membrane i s used in courtship and  that there are interspecific differences suggests that these forms use the patterns i n species recognition.  By analogy i t is suggested that  photophores have a function parallel to that of color. function i s suggested by Tavolga (1958).  A further  In Bathygobius soporator the  males make low-pitched grunting sounds to attract the female, apparently by forcible ejection of water through the g i l l openings (in which the branchiostegals would take part). Sensory In some fishes modified branchiostegals have a sensory function. In both Mullidae and Polymixiidae the anterior branchiostegal becomes free from the branchiostegal membrane and forms a long barbel-like structure.  Of the Mullidae, Herald (1961) says "The long, tactile  barbels under the chin, constantly working i n the same way as a mine detector as they are dragged over the bottom, enable the goatfishes to locate small items of food that might otherwise be missed.  These barbels  21  are highly flexible, often moving back and forth even when the goatfish is at rest.  When not in use, the barbels can be pulled under the throat,  where they are f a i r l y inconspicuous."  According to Andriashev (1944)  the barbels in Hullus are also employed in digging and chemoreception. As the polymixiids are deepwater forms, l i v i n g between 600 and 1200 feet, their habits are not well known.  Through analogy with the  barbels of Mullidae i t i s possible to suggest that they also have a sensory function.  It is d i f f i c u l t to conceive of any other function.  In Linophryne coronata the hyoid barbel "was found to be formed of a nerve issuing from the hind corner of the mandible and of a strand of the interhyoideus muscle. Protection of G i l l s The branchiostegal series serve to protect the g i l l s .  In some  forms lacking branchiostegals, scales have assumed the protective function (Mesturus), in others the lateral gulars have expanded to replace them (Polypterus). Defense and Protection In certain eleotrids such as BelobranchU3, the base of one or more branchiostegals is pointed and projects from the skin.  By analogy i t  i s conceivable that this spine or spines is used as a deterrent defensive mechanism (similar to the suborbital spines in Cobitidae, maxillary spines of Notacanthidae, caudal peduncle spines of Acanthuridae). Many acanthopterygian fishes have spines on the opercular bones, probably of similar function.  Other fishes, such as Denticipitidae have small  22 spinules on the branchiostegals. to understand.  The function of these is more difficult  Morris (1955) has experimentally demonstrated the  protective value of dorsal spines in sticklebacks.  A pike which had  been pricked in attempting to swallow a stickleback was less likely to make the attempt again.  THE ORIGIN OF THE BRANCHIOSTEGAL SERIES The Branchiostegals In exploring the origin of branchiostegal rays i t is necessary f i r s t to examine the earliest teleostome fossils.  Although fragmentary  f o s s i l teleostomes are found in the Lower Devonian deposits, i t is not until the Middle Devonian that adequate specimens are known.  In the  Middle Devonian the three major early teleostome subclasses, Actinopterygii, Crossopterygii and Dipneusti are already clearly distinguished (the subclass Brachiopterygii not being known until the Eocene).  In a l l of these we find broad, flat, spathiform branchiostegals,  a median gular and a pair of lateral gulars and operculum and a suboperculum.  The branchiostegal series of these subclasses are much more  similar than in modern representatives of the groups, as the later Actinopterygii tend to lose the gulars while the Dipneusti and Crossopterygians lose the branchiostegals.  It i s also notable that the  opercle and particularly the subopercle are more similar to the branchiostegals, than are the opercle and subopercle in more modern teleosts.  However, i t is evident that the branchiostegal series is  already quite well developed in the earliest teleostome remains and that i t i s therefore necessary to examine the forerunners of teleostomes to determine the origin of the branchiostegal series. of the teleostomes are not known with certainty.  The forerunners  However, most evidence  points towards origin from the Acanthodii or a closely related group. The Acanthodii are sufficiently ancient to be ancestral to the teleostomes (unlike the Elasmobranchii). The Acanthodii agree with the Teleostomi in possession of true bone in the skeleton, jaws, circumorbital  24 bones, ganoid type scales, similar neurocrania (Watson, 1938), shaped branchial arches, small o l f a c t o r y organs and large anterior o r b i t s . Berg  (1947)  indicated the two o t o l i t h s i n Acanthodes are similar to  palaeoniscid o t o l i t h s .  Of the s i m i l a r i t y of the scales of Acanthodii  and A c t i n o p t e r y g i i Aldinger (1937, translation) states "In contrast (to important differences between Acanthodii and R h i p i d i s t i a ) the scales of Acanthodii are b u i l t after the same plan as those of the oldest Elonichthyiformes and of C h e i r o l e p i s " . Both the Acanthodii and early Teleostomi are found i n freshwater deposits.  (1955),  Arambourg (1958a), Romer  H i l l s (1943) agree that the Acanthodii or forms close to i t  gave r i s e to the Teleostomi.  Berg  (1947)  Acanthodii are a l l i e d to the Teleostomi."  considers ... "that the Watson (1938), i n a r e v i s i o n  of the Acanthodii, considered that the Acanthodians had no close relationship with the bony f i s h , xi/hile admitting, "Nevertheless there i s a most curious set of q u a l i t i e s i n which the members of two great groups agree."  But he d i d regard the Teleostomi as derived from the Class  Aphetohyoidea i n which he included the Acanthodii.  In summary then i t  i s quite probable that acanthodians or close gnathostome r e l a t i v e s were ancestral to the Teleostomi, and i t i s thus then i n the Acanthodii that the o r i g i n s of branchiostegals rays are here sought. From the v i s c e r a l arches i n the Acanthodii extend rows of bony splints.  I t i s possible that from these the branchiostegal rays .  developed, as has been suggested by Gregory (1951).  The  anteriormost  of these rows bony s p l i n t s i s w e l l developed, the rays being large and r o d - l i k e dr paddle-like and forming an operculum.  Watson (1938) believed  25  that this row of rays w a 3 carried by the mandible, (the rays being retained from a time when the jaws were g i l l bars) and that a f u l l s l i t separated the mandibular and hyoid arches.  gill  He supported this theory  by showing the hyoid arch had a set of g i l l rakers along i t s whole length and suggesting that these guarded a f u l l g i l l s l i t before the hyoid arch.  If there was a f u l l s l i t between the hyoid arch and  mandibular arch and not just a small or large dorsal spiracle, then the well developed row of visceral rays must have proceeded from the mandibles. It i s not, however, definite that this operculum was mandibular. In certain of Watson's photographic plates (plate 5 of Climatius and plate 7 of Euacanthus) the hyoid arch has been displaced posteriorly and has carried with i t the operculum.  In Davis (16*94> p i . 27, f i g . 1 and  l a of Acanthodes) the hyoid rays are seen to insert on the ventral face of the hyoid arch.  If the rays were closely applied to the mandible i t  would appear they would interfere with opening of the jaws as opening the jaws meet with resistance as the rays wore forced upon one another. The branchiostegals of palaeoniscids appear in lateral view to insert upon the mandible while they are actually inserting on the underlying hyoid arch.  Stensio (1947) doubted that there was a f u l l hyoid g i l l  s l i t and that the principal operculum was mandibular. He also mentions that Holmgren has come to a similar conclusion.1  A further paper has just been published which also supports this view. Westoll, T.S. 1963. The hyomandibular problem in placoderm fishes. Proc. XVI Int. Zool. Congress 1: 176.  26 From the above arguments three hypotheses may be made.  If the  principal operculum i s mandibular the branchiostegals may be derived from:  i ) the smaller hyoid rays behind the principal operculum, the  principal operculum later being lost, or i i ) the rays of the principal operculum which became attached to the hyoid arch on closure of the spiracular s l i t .  But i f the rays of the principal operculum were  indeed hyoidal i t can be suggested:  i i i ) that they remained and  developed into the branchiostegals.  To the author the third hypothesis  seems most economical and preferable.  However, through sectioning of  the hyoid-mandibular region of acanthodian fossils i t would be readily determinable which theory i s true. The operculum and suboperculum The operculum and suboperculum, found in the f i r s t known teleostomes, are probably expansions of branchiostegals or their hyoid ray homologues, as has been suggested by Traquair (in Ridewood, 1904) and by Hubbs (1920). L i t t l e difference but size may be seen between the opercular, subopercular and branchiostegals of primitive teleostomes.  The embryological  development of the operculum and suboperculum i s very similar.  One can  see in some acanthodians (e.g. Euthacanthus) a tendency towards expansion of certain opercular rays.  It does not seem unreasonable, therefore, to  suggest derivation of the operculum and suboperculum from branchiostegals or hyoid rays. With the expansion of branchiostegals into opercular bones larger muscles might insert upon them and a stronger branchial pump develop. A stronger branchial pump may have developed purely for the sake of  27  efficiency or because of greater respiratory demands. would require more oxygen.  Greater activity  The acanthodians are known, through a  fortunate fossi3.iza.tion (Watson, 1959) to have cyclootome type myomeres with a low central vertex and no horizontal septum.  It might be  suggested that this type of myomere indicates a lower activity level than would the more highly developed piscine myomere type (Nursall, 1956) found in teleostomes.  It might alternately be suggested that during  teleostome evolution, conditions of lower oxygenation due to warmer climate produced selection for a more efficient branchial pump.  Either  of these two factors might explain the evolution of opercular bones from branchiostegals. The Interoperculum The interoperculum i s absent from the Dipnoi, Crossopterygii, Brachiopterygii and lower Actinopterygii. Ospiiformes of the Lower Triassic.  It i s f i r s t found in the  Regan (1929) siiggested that the  forward migration of the mandible and quadrate dragged the suboperculum down, perhaps causing the lower end of the suboperculum to be fractured and pulled forward to form the interoperculum. rather Lamarkian.  This explanation appears  The following hypothesis would appear to be preferable.  Several authors have suggested that the interoperculum developed from a forwardly displaced branchiostegal (Cole and Johnstone 1902 in Ridewood, 1904; Westoll, 1944; Saint-Seine, 1955). The development of an interoperculum seems to have been a further development in the separation of the mandibles and operculum. The preoperculum developed in the teleostome ancestors, partially separating  28  the jaw and opercular movements.  With the freeing of the maxillary in  the Ilolostei the need again arose to increase separation of the jaws and operculum to make their movements more independent from one another. The evolutionary solution was the interpolation of the upper.nost branchiostegal between the jaws and the suboperculum; thus, the uppermost branchiostegal became the interoperculum.  Schaeffer (1956) has shown  there i s a high degree of correlation between the freeing of the maxillary and the presence of an interoperculum. An element in the chondrostean Platysiagum has been termed by Brough (1939) a modified branchiostegal or an incipient interoperculum. This element l i e s in a slight concavity under the front two thirds of the suboperculum.  The element cannot be identified as an interoperculum  since i t does not separate the jaws from the suboperculum, nor is i t broadly bordered by the preoperculum.  It i s very similar to the upper-  most branchiostegal of the chondrosteans Ptycholepis and Brookvalia which l i e in a slight emargination of the suboperculum.  It therefore  seems inadvisable to c a l l this element an incipient interoperculum. The Gular Plates Both median and lateral gular plate3 are found in the earliest of the actinopterygian, crossopterygian and dipnoan teleosts.  The lateral  gulars are hardly distinguishable (only by being slightly larger and bearing a pit line) from the adjacent branchiostegals in the earliest teleost fossils (Cheirolepidae).  Indeed there is no reason to suppose  that the lateral gulars are not simply expanded branchiostegal rays. The lateral gulars are already characteristically large in the earliest  29 crossopterygians.  As the crossopterygians evolve the lateral gulars  eventually supplant both the median gular plate and the branchiostegals. The branchiostegals and median gular are also lost during the evolution of the Dipnoi.  The Brachiopterygii also lack a median gular and  branchiostegals, the large lateral gulars have supplanted them. The pit lines are of great value in tracing the gular elements. The median gular of Crossopterygians and Actinopterygians may be identified by a V-shaped pit l i n e .  The lateral gulars of a l l four sub-  classes, at least primitively bear a transverse pit l i n e .  In the  Crossopterygians (osteolepids) one or two of the branchiostegals under the end of the mandible may bear a short pit l i n e .  These appear to have  been retained in the dipnoans where the anterior of the two marked branchiostegals has moved to the medial edge of the posterior branchiostegals.  In the Dipnoi there are primitively two pairs of  lateral gulars, the posterior pair of which bears the pit line and which is thus identifiable with the lateral gulars of the other suborders. The second pair of gulars may have formed by division of the single crossopterygian pair, or by expansion of one of the anterior branchiostegals.  The f i r s t suggestion i s favoured since the gular pit  lines s t i l l retain a position (at the anterior end of the posterior gulars) that would be in the centre of the single gular, although i t is now divided into two.  If the anterior gulars were formed from expanded  branchiostegals one might expect the pit lines on the posterior gulars to be in the middle of the gular rather than at the anterior end. The origin of the median gular i s less certain. from which i t can be derived.  There is no bone  However, i t is possible that i t arose  30 from a branchiostegal close to the midline.  This i s difficult to conceive  as the median gular overlies the branchiostegals and i s not in the same plane.  It i s possible that i t arose de nouveau from dermal tissue.  perhaps i t evolved from the hyoid rays of the Acanthodii.  Or  The hyoid  rays are continuously distributed around the hyoid arches in the Acanthodii, not restricted bilaterally as in the Teleostomi.  Possibly  the median hyoid ray of the Acanthodii gave rise to the median gular.  31 PHYLOGENETIC OR VERTICAL EVOLUTION The phylogenetic or vertical evolution of branchiostegals as opposed to adaptive or horizontal evolution is traced in this section. The phylogeny of the operculars, gulars and hyoid arch elements is also traced but in less detail.  The groups are treated in phylogenetic order,  as closely as i s possible in a linear series. phylogeny see plate XVIII.  For the best picture of  Evolution i s followed down to family level,  although occasionally comments may be made on lessor taxa.  An attempt  i s made to illustrate at least one example of every order, (see plates I, II, III, etc.).  32 CLASS TELEOSTOMI (OSTEICHTHYES INCLUDING DIPNOI) Branchiostegals (0-2)3-20(21-50).  One (or two) median gulars, one  or two pairs of lateral gulars present or absent.  Operculum, suboperculum  and (in higher groups) iivteroperculum usually present, but sometimes absent.  Interhyal, epihyal (in higher groups), ceratohyal and one or  two (in higher groups) hypohyals usually present but sometimes lost. Lower Devonian to present.  Four subclasses and 66 orders, 38 of which  are l i v i n g . Although the subclass Actinopterygii i s considered most primitive, then the Crossopterygii, Dipneusti and Brachiopterygii, the latter are placed f i r s t because they are more primitive than the higher Actinopterygii. The Brachiopterygii might best be placed as a chondrostean order of the Actinopterygii.  But u n t i l i t s affinities are known with certainty i t  would appear preferable to leave i t in a separate  subclass.  The Dipneusti are often included in the same class as the other bony fishes, but Berg isolates them in their own class.  Since the  Dipneusti are derivable from the Crossopterygii and since they are not distinguished to a higher degree than the other subclasses of teleostomes they are included in the Teleostomi, not in a separate class. KEY TO TELEOSTOMI BASED ON THE BRANCHIOSTEGAL SERIES AND HYOID ARCH The following key outlines the major events in the evolution of the Teleostomi.  While i t follows the phylogeny rather closely, for the best  picture of phylogeny of the Teleostomi see the evolutionary dendrogram. For the keying out of groups and determining of relationships one cannot depend on one set of characters, so that some orders cannot be  33 separated in this key.  The key demonstrates that at many points in  evolution that the branchiostegals and hyoid arch provide sharp division between related groups.  For example the Beloniformes are separated  from a l l other malacopterygians by the lack of an interhyal and nonfiliform branchiostegals, the Cyprinodontiformes and Gobiesociformes differ from a l l other ?.canthopterygians (except a genus of Gobiidae and Syngnathidae) in having lost one hypohyal, a different one in each case. The Tarasiiformes, Chondrosteiformes and Peltopleuriformes are neatly separated by branchiostegals.  Just as important are the similarities  shown among orders which cannot be conveniently separated on the basis of branchiostegals.  Thus, i s indicated the closeness of the great  proportion of the acanthopterygians. Key to the Classes of Gnathostoraes A  With jaws, laterally paired nostrils, 3 semicircular canals. B  Without rays on the hyoid arch . . . Pterichthyes, Coccostei.  BB  With rays on the hyoid arch. C  ;  .  CC  Lacking gular plates, an interhyal and opercular bones. ("Opercular plate" of holocephalans composed of fused hyoid rays). D  Hypohyal and ceratohyal present.  DD  Only ceratohyal present. (including Holocephali).  Class Acanthodii.  Class Elasmobranchii  With or without gular plates, with an interhyal (lost in some orders), with opercular bones (completely lost only in Giganturiformes and Saccopharyngiformes). Teleostomi.  Class  34  Key to Subclasses of Teleostomi The subclasses are difficult to separate in a convenient manner because the primitive members are so similar and because of the convergence between the Coelacanthiformes and Brachiopterygii. A  With one large pair of gulars longer than 2/3 of the mandible or with 2 pairs of gulars (except gulars absent in Ceratodiformes and Lepidosirenformes these recognizable because of cartilaginous disk under tip of operculum). B  With or without median gular and branchiostegals.  Medium-  sized subquadrate or subtriangular operculum with a broad or triangular suboperculum.  Where suboperculum is triangular  opercular fold passes behind i t . . . Crossopterygii. BB  With or without a median gular and branchiostegals.  Operculum  large and pentagonal (or reduced to a slender ray with a cartilaginous disk under i t s t i p ) .  Narrow elongate suboperculum  below . . . Dipneusti. BBB Without median gular or branchiostegals.  Operculum and sub-  operculum medium-sized and subtriangular; opercular fold in front of suboperculum . . . Brachiopterygii (contains a single order Polypteriformes). AA  With one pair of gulars shorter than g of length of mandible or without gulars . . . Actinopterygii Key to Orders of Crossopterygii  A  Branchiostegals and sometimes median gular present. taper along whole length towards anterior t i p .  Lateral gulars  Suboperculum  35  completely ventral to operculum. B  Branchiostegals 1 0 .  Supraorder 0steolepide3.  Suboperculum xdth ventral edge on the  dorsal edge of the lowest preoperculum (third) . . . Hoploptychiforme s. BB  Branchiostegals 4-8.  Suboperculum with ventral edge not on  dorsal edge of lowest preoperculum . . . AA  Branchiostegals and median gular absent.  Osteolepiformes.  Lateral gulars of even  breadth, do not taper through whole length towards anterior t i p . At least dorsal portion of suboperculum opposite front of lower portion of operculum.  Supraorder Coelacanthi . . . Coelacanthiformes.  Key to Orders of Dipneusti The following is a tentative key based on the assumption that the Uronemiformes have gular plates and that they and the Ctenodontiformes have less than three branchiostegals. A  Gular plates and usually branchiostegal(s) present. large and circular or pentagonal in shape. B  Branchiostegals 3 . . . Dipteriformes.  BB  Branchiostegals less than 3 . C  Operculum  Supraorder Dipteri.  Suboperculum 1/3 to ^ of size of operculum . . . Ph oneropleuriforme s.  CC  Suboperculum smaller. D  Operculum oval . . . Uronemiformes.  DD  Operculum scallop-edged, roughly circular . . . Ctenodontiformes.  AA  Gular plates and branchiostegals absent.  Operculum small and  36 elongate. Supraorder Ceratodi. E  Operculum arrowhead-shaped; suboperculum a slender ray . . . C er atodiforme s.  EE  Operculum a slender ray; suboperculum chevron-shaped . . . Lepido sireniformes. Key to Orders of Actinopterygii  Due to paucity of information, the orders Cephaloxeniformes, Aethodontiformes, Luganoiformes, and Ptycholepiformes must be omitted from this key. A  Interoperculum absent. (Chondrostei). B  Lateral gulars may be present.  Group I  (Maxillary not free from cheek, except Dorypteriformes).  With a pair of lateral gulars and usually with a median gular. Always with a suboperculum. C  With 4 or more branchiostegals D  With pit line on lateral gulars . . . Palaeonisciformes, Perleidiformes.  DD  Without pit line on lateral gulars . . . Pholidopleuriformes.  CC BB  With 1-3 branchiostegals . . . Haplolepiformes.  Without lateral and median gulars. E  With or without suboperculum.  With suboperculum (except Polydontoidei). F  Branchiostegals 3 or more. Tarasiiforme3 15 branchiostegals. Platysiagiformes 12 branchiostegals.  Phanerorhynchiformes "series" of branchiostegals. . . . . . Chondrosteiformes 9 - 1 0 branchiostegals. . . . . . Peltopleuriformes 6 - 7 branchiostegals. FF  Branchiostegals 0 - 1 . G  Operculum smooth . . . Redfieldiiformes.  GG  Operculum grooved or incised . . . Acipenseriformes.  EE  Without suboperculum H  Operculum deeper than long . . . Dorypteriformes, Bob as atr aniiforme s, Pycnodontiforme s.  HH  Operculum as long as deep . . . Saurichthyiformes.  Interoperculum present (secondarily absent in Lepidosteiformes, some Mormyriformes, Giganturiformes, Saccopharyngiformes, some Anguilliformes).  Lateral gulars never present.  (Maxillary free  from cheek). I  A single hypohyal present, a median gular often present. Group II (Holostei). J  Median gular present. K  Branchiostegals 3 0 or fewer . . . Ospiiformes, Amiiformes, Pholidophoriformes.  KK  JJ  Branchiostegals 3 0 - 5 0 . . . Pachycormiformes,  Median gular absent, Branchiostegals 3 . . . Lepisosteiformes. Branchiostegals 1 2 - 1 3 . . . Aspidorhynchiforra.es.  II  Two hypohyals present (except Lycopteridae, Phractolaemidae,  Mormyriformes, Amphiliidae, Chacidae, Anguilliformes, Stylephoridae, Beloniformes, Gobiesociformes). Albuloidei. L  some Syngnathidae,  Cyprinodontiformes  Median gular only in Elopoidei and  Group III (Teleostei).  Branchiostegals 0 - 3 6 , one or more of upper branchiostegals often spathiform (except Stomiatoidei, Myctophiformes, Mormyriformes, some Cypriniformes, Notacanthif ormes, Anguilliformes).  Epihyal and ceratohyal  sutured together only in Siluroidei and Beloniformes. Never spines on opercular bones.  Branchiostegals  usually inserting on external face of hyoid arch with a minority below on the ventral or internal, sometimes a l l on ventral edge; only sporadically in Clupeiformes (Hiodontidae, Chanidae, Gonorhynchidae, Osmeridae, Argentinidae) and commonly in the Myctophiformes is the acanthopterygian pattern of the 4 upper branchiostegals on the external face and 0-5 lower ones on the ventral (or internal) face of the hyoid arch found.  Group IIIA  Malacopterygi. M  With branchiostegals, N  hyoid arch and operculum.  Hypohyals 2 (except Phractolaemidae, Araphiliidae and Chacidae).  0  One or more upper branchiostegals spathiform, at least distally  ...  Clupeiformes, Cypriniformes 00  Branchiostegals not spathiform.  P  Branchiostegals not straight, curve up behind g i l l cover . . . Myctophiformes.  PP  Branchiostegals nearly straight, do not curl up behind g i l l cover . . . Notacanthiformes. NN  Hypohyals 0-1 Q  Branchiostegals not filiform and not curled up around dorsal edge of operculum.  QQ  R  With interhyal . . . Mormyriformes.  RR  Without interhyal . . . Beloniformes.  Branchiostegals filiform and curled around operculum . . . Anguillifonnes.  MM  Without branchiostegals or operculum . . . Giganturiformes, Sac coph aryngif orme s.  LL  Branchiostegals 1-9 (10) (except 8-11 in Echeneiformes). Branchiostegals acinaciform, sometimes filiform, never spathiform (except Molidae).  Epihyal and ceratohyal usually  sutured together (but suture secondarily lost in several groups).  Often spines on operculum, sometimes on suboperculum  and interoperculum.  The upper 4 branchiostegals on the  external face of the hyoid arch, the other 0-7 (usually 2-3) on the ventral or internal face. S  Group IIIB Acanthopterygi.  Hypohyal3 2 (except in one genus of Syngnathidae, Gobiidae and Stylephoridae and a l l the Phallostethidae). T  Branchiostegals modally 7 or more.  G i l l membranes  usually separate (except some Gadiformes) . . . Beryciformes, Zeiformes, Lampridiformes,  Bathyclupeiformes, Gphidiiformes, Gadiformes, Ateleopiformes, Echeneiformes. TT  Branchiostegals rnodally 6 or less.  G i l l membranes  separate, united and free from isthmus, or joined to isthmus . . . Percopsiformes, Syiignathiformes, Perciformes, Pleuronectiformes, Tetraodontiformes, Icosteiformes, Gasterosteiform.es,  Mastacembeliform.es  Synbranchiiformes, Batrachoidiformes, Lophiiformes, Pegasiformes. Hypohyals 1 U  Lower hypohyal present.  With epihyal-ceratohyal  suture . . . Cyprinodontiformes. UU  Upper hypohyal present.  Without epihyal-ceratohyal  suture . . . Gobiesociformes.  41 SUBCLASS CROSSOPTERYGII Branchiostegals 1 0 or fewer; median gular present or absent, primitively with a V-shaped pit line; a single pair of large gulars at least 2/3 the length of the mandible; operculum present; usually suboperculum present; hypohyal, ceratohyal and interhyal present. Devonian to present.  Lower  Two superorders with three orders and 1 2 families. SUPERORDER OSTEOLEPIDES  Branchiostegals and median gular present (median gular in Hoploptychiformes?).  The lateral gulars taper along their whole length  towards the anterior t i p .  Suboperculum ventral to operculum and taking  normal part in movement of g i l l cover. Carboniferous.  Two orders.  Thomson  Lower Devonian to Upper  (1962)  would reduce the status of  these two orders.  / ORDER HOPLOPTYCHIFORMES Branchiostegals 10; median gular unknown; a pair of large lateral gulars with an arc-shaped pit line; operculum and suboperculum present lower edge of suboperculum on upper edge of third preoperculum. Lower to Upper Devonian.  TITO  families. ^  Branchiostegals:  No data available. ^  Branchiostepials;  Porolepidae  Hoploptychidae  In Hoploptychius flemingi about 1 0 .  The f i r s t six  are elongate and situated in a series below the suboperculum. The remaining four are very short and l i e between the gulars and the  42 mandibles; the f i r s t of these bears a short vertical pit l i n e .  At least  two of these short branchiostegals are known in Glyptolepis. Gulars:  One of Woodward's specimens of Hoploptychius flemingi shows  the lateral gulars but no median gular nor does his text report a median gular in Glyptolepis*  The lateral gulars in Hoploptychius are large,  about the same length as the mandible.  The posterior edge of the lateral  gulars curve inward and anteriorly, leaving a V-shaped gap.  At the  centre o f each gular is a short arc-shaped pit line with apex anteriormost. Operculars:  The operculars of Hoploptychius are rather different from  those i n 0 s t e o l e p i 3 since they insert on the diagonal base of the upper preopercular (squamosal), rather than on the vertical base of the lower preoperculum as in Osteolepis.  Thu3 the opercular bones are more dorsal  in Hoploptychius and their bases diagonal. the suboperculum.  The operculum i s larger than  The jaw of Hoploptychius i s shorter than in Osteolepis  and the triangular lowest preoperculum acts an interoperculum of the holostean type, a piviting point for the opercular bones. Relationships:  The more numerous branchiostegals would indicate this  order to be more primitive than the Osteolepiformes. and number of branchiostegals separate the two orders.  The opercular bones Yet the two  orders share features which separate them from the Coelacanthi:  their  gular plates taper anteriorly, they possess branchiostegals and the suboperculum i 3 below rather than anterior to the operculum. References:  Jarvik (1948), Woodward (1891), Stensio (1947).  43 /  ORDER OSTEOLISPIFORMES (RIHZ0D0NTIF0RME3)  Branchiostegals 4-8;  visually a median gular with p i t l i n e ;  one  p a i r of large l a t e r a l gulars with p i t l i n e ; suboperculum not with lower edge on upper edge of t h i r d preoperculum; operculum and suboperculum present*  Six f a m i l i e s .  Taxonomy!  Middle Devonian to Lower Permian.  The operculars, gulars, branchiostegals and other s k u l l bones  of Rhizodontiformes  are so similar i n form and arrangement I f e e l  constrained to return t h i s order to the Osteolepiformes,  as Arambourg  (1958) has done.  ^ Branchiostegals;  Gyroptychiidae  In Gyroptychius branchiostegals 6-8.  almost quadrangular but expands d i s t a l l y .  The f i r 3 t i s  The remainder are short and  broad and bridge the gap between the gulars and the mandible.  The  second i s characterized by a diagonal p i t l i n e somewhat anterior to the center.  The l a s t two branchiostegals may fuse i n t o a single large p l a t e .  Gulars:  The diamond-shaped median gular bears a broad V-shaped p i t l i n e .  The l a t e r a l g u l a r 3 are large, narrow a n t e r i o r l y to a point and bear a short arc-shaped p i t l i n e at the centre of the side next to the mandibles. The p o s t e r i o r edges of the plates curve a n t e r i o r l y and medially, leaving a wedge-shaped gap between them. the mandibles.  The gulars are about % the length of  The anterolateral portion of the gulars contacts the  mandibles (a primitive character).  Operculars:  Tne operculum and suboperculum are small and rectangular.  The operculum Is s l i g h t l y l a r g e r .  The opercular bones are s l i g h t l y  44 shorter than i n Osteolepis. Taxonomy:  This family erected by Berg (1955)•  Relationships:  The branchiostegal series speak f o r a very close  relationship to the Osteolepidae.  References:  Berg (1955), Jarvik (1948).  ^  Osteolepidae PI. I about 7 spathiform  Branchiostegals:  In Osteolepis macrolepidotus  branchiostegals.  The f i r s t , broad but elongate, i s under the suboperculum,  which i t much resembles.  The remainder of the branchiostegals are  short and wide; they span the gap between the gulars and the mandible. The second and sometimes the t h i r d branchiostegal bear a small arcshaped p i t l i n e . labels.  These two p i t l i n e s are important  because they act as  They provide evidence that these two branchiostegals are  homologous to the two p i t - l i n e - b e a r i n g branchiostegals between the gulars and the mandible i n Dipterus and further that the bone called suboperculum i n Dipterus i s indeed that bone. °^ i l l macrolepidotus  The p i t l i n e on the t h i r d branchiostegal  i s apparently i n the process of being l o s t , since  i t i s often not present. In Osteolepis panderi there are only 4 branchiostegals, the anterior ones being displaced by the l a t e r a l gulars; i n Thursius there are 5-6 much as i n Osteolepis. the second with a p i t l i n e .  The branchiostegals  narrow anteriorly as the l a t e r a l gular approaches the jaw, u n t i l the f i r s t branchiostegal becomes pointed.  45  Gulars:  In Osteolepls a small diamond-shaped median gular is located  in the fork of the mandibular rami.  It bears a V-shaped pit line, the  arms of which curve slightly outward.  The very large lateral gulars  nearly equal the length of the mandibles. anteriorly.  They taper only slightly  The posterior edge curves inward and anteriorly.  In the  middle of each lateral gular i s a short arc-shaped pit line whose apex faces anteriorly. in their length.  The width of the lateral gulars enters about 3 times In Thursius the gulars are pointed anteriorly and  about .9 of the mandibular length.  They bear a pit line and their  posterior edges curve medially and anteriorly. Operculars:  In Osteolepis the operculum is slightly larger than the  suboperculum; both are elongate in horizontal direction and very similar in shape.  The operculum of Thursius i s said to be deeper than broad and  the suboperculum smaller and to be broader than deep. References;  Woodward (1891), Berg (1947, 1955), Jarvik (1948). ^ Euathenopteridae Pl.  Branchiostegals:  I.  In Eusthenopteron foordi 8 branchiostegals.  The f i r s t  i s elongate and l i e s below and slightly anterior to the suboperculum. The remainder are very short and are situated between the gulars and the mandible; the f i r s t of these bears a vertical pit line; the last is triangular. Gulars;  In Eusthenodon 8.  A small median gular with an arc-shaped pit line with apex  anteriormost is present, an unusual shape for this pit l i n e .  The lateral  46  gulars are relatively small—about 2/3 of the length of the mandible. They are narrow (their width entering 4*5 times in the length) and f a i l to touch the mandible anteriorly.  Slightly anterior to their centre is  a J-shaped pit line, instead of the usual arc-shaped or straight l i n e . Operculars;  The operculum and suboperculum are of about equal size and  trapezoidal in shape. Taxonomy;  Berg (1955) erected this family.  Relationships:  This family differs from other Osteolepiformes by the  shorter and narrower lateral gulars.  It i s closest to Osteolepidae in  this respect. References:  Berg (1955). Jarvik (1944, 1952), Bryant (1919). f Rhizondontidae  Branchiostegals;  In Rhizodppsis sguroides there are 5 branchiostegals.  The f i r s t of these i s elongate and situated under the suboperculum  0  The  remaining 4 l i o between the lateral gulars and the mandibles; they narrow anteriorly u n t i l the f i r s t i3 triangular. Gulars:  In Rhizodopsis a small anterior median gular i s followed by a  large pair of gulars.  The median gular, situated in the fork of the  mandibles, i s egg shaped with apex anteriormost.  Behind i t are the pair  of large lateral gulars whose length almost equals that of the mandible. Their posterior edge curves inward and anteriorly.  The l e f t is shown to  overlap the right in Woodward's f i g . 57. The anterior tip of the lateral gular touches the mandible.  The length of the gular i s about 2^ times  47  i t s width. Operculars:  The operculum in Rhizodopsis ornatus is scallop-shaped  (with hinge uppermost) and heavily decorated. and pentagonal in Rhizodopsis.  The operculum is large  The smaller suboperculum i s approximately  trapezoidal. Relationships:  The operculars, gulars and branchiostegals are very  similar to those in other Osteolepiformes. References:  Woodward (1891), Traquair (1883). J.  ' Parabatrachidae Branchiostegals: Gulars:  No data available.  A pair of lateral gulars, each about Z\ times as long as wide,  abruptly truncated posteriorly or rounded in Parabatrachus (= Megalichthys Agassiz). Operculars:  Operculum nearly as broad as deep.  References:  Woodward (1891).  48 SUPRAORDER COELACANTHI (ACTINISTIA) Branchiostegals and median gular absent. breadth, tapering only at tips.  Lateral gulars of even  Suboperculum at least partially  opposite lower portion of operculum, and apparently not taking part in movement of g i l l cover.  Middle Devonian to present.  One order.  ORDER COELACANTHIFORMES A large pair of lateral gulars of even breadth bearing an arcshaped pit line.  Suboperculum at least partially opposite lower portion  of operculum. Suboperculum apparently not taking part in movement of the g i l l cover. present.  Interhyal and ceratohyal present.  Middle Devonian to  Three suborders, four families.  Taxonomy: There are no notable differences i n the branchiostegal series between the three suborders of Coelacanthiformes, but they may be separable on other grounds. Arambourg (1958) does not employ the suborders i n his classification. Relationship:  The Coelacanthiformes are more similar to the  Osteolepiformes than to the Hoploptychiformes  i n that the suboperculum  is next to the third preoperculum, i n that the branchiostegals are fewer i n Osteolepiformes and i n that the sensory canals of the head, as portrayed by Stensio (1947), are of a more similar pattern. f SUBORDER DIPLOCERCIDOIDEI Middle Devonian to Upper Devonian. A single family.  49 f Diplocercidae Gulars:  In Nesides schmidti a pair of large lateral gulars, length  about 5/6 of the mandible.  Posterior end protruding slightly beyond  mandible. Operculars:  Operculum large and triangular, concave where i t meets the  upper preoperculum.  Between the lower portion of the operculum and the  preoperculo-quadrajugal is a small presumably triangular suboperculum. The suboperculum i s anterior and not ventral to the operculum. Taxonomy: References:  Romer (1955) i s followed as to the limits of this family. Stensio (1947). ^ SUBORDER LAUGIOTJJEI  Lower Triassic.  A single family. / Laugiidae  Gulars:  A pair of large lateral gulars 7/8 of the length of the  mandibles.  Breadth even, about 3z times their length.  L i t t l e gap  posteriorly between the gulars. Operculars:  Operculum medium sized and triangular.  corner pointed, without notch. Relationships:  Suboperculum not known, presumably absent.  The opercular bones are l i t t l e different from those in  the Coelacanthoidei. References:  Antero-dorsal  Stensio (193 2 ).  50  SUBORDER COELAGANTHOIDEI Lower Carboniferous t o p r e s e n t .  Two families.  Coelacanthidae PI. I Gulars:  There are a pair of large lateral gular plates in members of  this family.  In Rhabdoderma elegans t h e gulars are about 4/5 the length  of the mandible and do not protrude posteriorly beyond t h e end o f t h e mandible.  In R. aldingeri the width i s hh times the length and the main  body of the plate is of even breadth, tapering only at the tips.  In  Holophagus (=Undina) the gulars are of even breadth—about 3 times in length; they are about equal to the length of the mandible and just posteriorly from i t .  In Macropoma the gulars are almost equal to t h e  length of the mandible and bear arc-shaped pit lines centrally. I n Diplurus the gulars are long and narrow, the width kk  i  n  length. I n  Whiteia the gulars occupy only about 2/3 of the mandibular length; they are of even breadth.  They bear a short straight pit line centrally.  Their posterior ends are rounded but they soon meet on the midline so there i s not a V-shaped gap between them. Operculars:  In Rhabdoderma the operculum is of middling size and  triangular; i t has a notch where the antero-dorsal corner meets the spiracular bone.  The suboperculum i s small and triangular and the upper  half i s opposite the lower end of the operculum.  In Holophagus (=Undina)  the operculum i s longer, extending further ventrally than in Rhabdoderma and the suboperculum i s a long or short triangle, 2/3 or more of which  51  i s below the operculum.  The operculum i 3 also larger in Wimania ( h a 3  an antero-dorsal notch) and Axelia (lacks notch).  In Macropoma the  operculum i s of middling size and has a small concavity on i t s dorsoanterior edge; a small rectangular suboperculum i s present.  In  Mylacanthus the large operculum has a lobate or spinous posterior margin. In Whiteia the operculum i s medium sized, triangular, and has a slight concavity on i t s dorso-anterior corner where i t contacts the postspiracular. A small suboperculum is present.  In Diplurus the operculum i s medium  sized, triangular, and without an antero-dorsal notch; the dorso-posterior edge is crenulate; the suboperculum unknown. Hyoid arch:  In Macropomus ceratohyal with postero-ventral projection;  cylindrical interhyal. References:  Moy-Thomas (1937), Zittel (1887), Stensio (1921, 1932),  Lehman (1952), Schaeffer (1952), Goodrich (1909), Gardiner (I960). Latimeriidae Gulars: present.  In Latimeria chalumnae a pair of large lateral gulars i s These are only slightly less than the length of the mandible.  They are of even breadth, and taper at the ends to a point. l i t t l e more than 3 times in length.  Width is a  An arc-shaped pit line i s present  in the centre of each gular; as usual the apex of the arc is anteriormost. Operculars:  Operculum middle sized, a rounded triangle without antero-  dorsal notches.  Suboperculum small and forming a narrow triangle the  apex uppermost.  The suboperculum l i e s entirely in front of the lower  52 half of the operculum. The opercular fold in Latimeria, unlike in other orders of fishes, passes between the operculum and the suboperculum.  The close attachment  of the suboperculum to the dorsal operculum and the passage of the opercular fold behind, rather than in front of the suboperculum, would seem to forbid the suboperculums taking part in the movement of the g i l l cover.  From the similar arrangement of the opercular bones in other  families of the order Coelacanthiformes one would conclude that the rigidity of the suboperculum also pertains to them.  In this character  the Coelacanthiformes differ from other crossopterjrgians and other teleostomes.  J . L . B. Smith, from a poorly preserved specimen, reported  an interoperculum.  Thi3 bone i s known only from the higher Actinopterygii.  Schaeffer suggests Smith s interoperculum may be modified scales in the t  opercular membrane.  Millot and Anthony do not report an interopercular  in their study of well preserved specimens and i t seems most unlikely i t occurs in Latimeria. Schaeffer (1952) interprets the suboperculum as a preopercular bone in the Coelacanthoidei.  This suggestion has the merit of explaining the  rigidity of the "suboperculum" and i t s unusual anterior position in this group.  In the other crossopterygian orders the suboperculum i s directly  ventral. Hyoid arch;  Consists of a short cylindrical hypohyal, a ceratohyal,  epihyal and hyomandibular. References:  Millot and Anthony (1959), Smith, J . L . B. (1940).  53  SUBCLASS DIPNEUSTI Branchiostegals three or less; median gular present or absent; 1 - 2 pairs gulars present or absent (combined length of lateral gulars exceeds one half mandible length); operculum present and suboperculum present (probably inserting on hyomandibular); a hypohyal present or absent; a ceratohyal always present; an interhyal may be present. Devonian to present.  From late Early  The dipneustians are divided into two superorders,  the Dipteri and the Ceratodi, 6 orders and 1 2 families. The Ceratodi have a complete branchiostegal series and full-sized operculars while the Dipteri have lost the gulars and branchiostegals and have reduced operculars.  The Dipteri are readily distinguished from  other fishes by their greatly expanded pentagonal operculum while the Ceratodi are distinguished by their very reduced operculum. The differences in the branchiostegal series alone certainly justify the supraordinal separation of the Ceratodi and Dipteri.  The differences  between the two make i t d i f f i c u l t to characterize the subclass Dipnoi as a whole.  However, the differences should be not unduly weighted,  since  they are concerned mainly with a loss or reduction in characters. The suboperculum rests on the ceratohyal unlike other fishes, in which i t usually rests on the hyomandibular or preoperculum. Further the suboperculum is much more slender than in other teleostomes, except in Scaumenacia.  It might therefore be questioned whether or not the  dipneustian subopercle i3 not a branchiostegal.  However the condition  of the subopercle in Scaumenacia. where i t i s of normal 3ize and shape, would seem to oppose this thesis.  Further, the unusual insertion of  54  the suboperculum may be accounted for by supposing that the great expansion of the operculum in the Dipteri has necessitated a lower insertion of the suboperculum and that i t has thus been displaced down from the hyomandibular to the ceratohyal.  This position has been  conservatively retained in the Ceratodi even though the size of the operculum has been reduced. The possession of branchiostegals, operculum, suboperculum, median and lateral gulars by primitive dipnoans shows clearly that they are related to the other subclasses of teleostomes.  But when they f i r s t  appear in the f o s s i l record they are already quite specialized, most branchiostegals are already lost and the gulars are more modified than primitive representatives of the other subclasses, and the operculum is considerably enlarged.  Although these features distinguish them, they  certainly do not warrant class distinction and the many similarities of the primitive members of the subclasses confirm their placement in a single class. The arrangement of branchiostegals and gulars in primitive dipnoans enable them to be derived from primitive Crossopterygii, but not vice versa.  This opinion is in agreement with that of Westoll (1949) who  believed that the Dipnoi either stemmed from the Rhipidistia, or that both groups have a common ancestor. such a common ancestor may be added:  To points listed by Westoll for a median gular, a pair of lateral  gulars with a pit line and broad short branchiostegals.  55  / 3UPER0RDER DIPTERI Gular plates present (Uronemiformes ?).  Branchiostegals present  in at least Dipteriformes and Phaneropleuriformes. roughly pentagonal.  Middle Devonian to present.  Operculum large, Ceratohyal present.  Four orders. ^ ORDER DIPTERIFORMES (RHYWCHODIPTERIFOWIES) Branchiostegals three, a small median gular and two pairs of gular plates, the posterior bearing pit lines; a large pentagonal operculum and a small elongate suboperculum present. to Upper Devonian.  From the late Early Devonian  Three families. "f" Dipnorhynchidae  Branchiostegals:  Two branchiostegals in Dipnorhvnchu3.  An elongate  branchiostegal l i e s below the suboperculum, which i t much resembles (in fact Westoll calls i t suboperculum 2).  Laterally between the anterior  and posterior gulars l i e s a second triangular branchiostegal (called by Westoll a lateral gular). Gulars:  Consists of a small anterior median gular, a pair of oval  anterior gulars which slightly overlap a larger posterior pair of gulars, and between the two pairs of gulars l i e s a second median gular. Operculars:  A large subrectangular operculum l i e s above a narrow  suboperculum, the latter much like the branchiostegal which l i e s below it. Relationships:  The gulars and branchiostegals are very similar to those  in Dipteridae although there is one less branchiostegal.  The possession  of  a pineal foramen, unique amongst the D i p n e u s t i , shows t h i s family i s  w e l l separated. order.  I t may, according to Berg (1947), dooerve a separate  Westoll considers t h i s f a m i l y v e r y p r i m i t i v e and shows  indications of relationship t o the R h i p i d i s t i a .  I t may be noted t h a t  the primitive crossopterygians a l s o p o s s e s s e d a p i n e a l foramen.  References:  Hills (1933), Westoll (1949). ^ Rhynchodipteridae  Branchiostegals: Gulars:  Not preserved.  Not preserved.  Operculars:  Operculum large, roughly quadrangular.  Suboperculum not  preserved. Taxonomy:  Berg (1947) provisionally placed this family in its own o r d e r j  Arambourg and Guibe (1958) place i t in the Dipteriformes. References:  Save-Soderbergh (1937). ^ Dipteridae Pl.  Branchiostegals:  II  In Dipterus 3 branchiostegals.  Between the posterior  gulars and the suboperculum l i e s a single spathiform elongate branchiostegal.  It resembles the suboperculum except that i t is somewhat  expanded distally, while the suboperculum tapers.  Just anterior to this  branchiostegal, between the gular and the angle of the jaw, are two very short accessory branchiostegals (about a quarter the length of the other).  57 The position of these is such that they do not f i t into a series with the branchiostegal; the second of these is below the f i r s t , not anterior to the f i r s t next to the mandible.  A pit lino runs across these two  accessory branchiostegals and onto the posterior gular plate.  This  reminds one strongly of the situation in the Crossopterygii where the second and third branchiostegals and the gular plate bear pit lines. But in the Crossopterygii the third branchiostegal i s anterior, not ventral and the pit lines on the three bones are separate, not in a straight line with one another.  However, the relationships seem  sufficiently close to suggest that the accessory branchiostegals are homologous with the second and third branchiostegal in primitive Crossopterygii and therefore that they are really branchiostegals and not displaced mandibular elements.  And finally i t appears that the  posterior pair of gulars in Dipterus are derived from the lateral gulars of the Crossopterygii.  The anterior pair of gulars in Dipterus may have  arisen by division of the lateral crossopterygian gulars into an anterior and posterior pair.  Enlargement of the anterior pair of gulars  would result in the posterior displacement of the posterior pair of gulars and the accessory branchiostegals and explain why they are out of line xclth the positions in the Crossopterygii. Gulars:  A small median anterior gular l i e s i n the fork of the  mandibular rami.  It i s not known to bear a V-shaped pit line as in  some Crossopterygii and Actinopterygii} nevertheless i t seems logical to consider i t homologous.  The median gular is followed by a medium-sized  pair of rhombic gulars.  The anterior pair of gulars lacks a pit line;  58  the posterior pair of gulars are somewhat larger.  Their posterior edges  curve anteriorly much a3 those in Crossopterygii, but they overlap more. The l e f t gular overlaps the right in both the anterior and posterior pairs.  The posterior gular bears a short straight pit line anteriorly;  apparently a continuation of the one running across the accessory branchiostegals.  A posterior median gular l i e s between the two paired  gulars. References:  Graham-Smith and Westoll (1937); Watson and G i l l (1923),  Westoll (1949). T  ORDER PHAWEROPLEURIFORMES  Branchiostegals two; a small median gular and two large pairs of gular3 present; a large operculum and medium-sized suboperculum present; ceratohyal known.  Upper Devonian.  Three families.  ^ Phaneropleuridae Branchiostegals: Gulars:  No data available.  A pair of long gulars, pointed anteriorly.  Operculars:  Operculum large and circular; suboperculum small and  elongate. References:  Woodward (1891), Whiteaves (1889).  59 ^ Scaumenacidae PI. II Branchiostegals:  In Scaumenacia two branchiostegals.  One short wide  spathiform branchiostegal which widens distally, and another anteriorly between the two paired gulars ("accessory branchiostegal").  These  correspond to the two in Dipterus. Gulars;  A small median gular l i e s in the fork of the mandible.  Behind  this is a relatively small anterior and a larger pair of posterior gular3.  The gulars a l l correspond with those in Dipterus, although  differing somewhat in form, being less elongate. Operculars;  There is a large pentagonal operculum with a curved  evacuation on i t s dorsal edge.  The small wide suboperculum curves up  from i t s lower edge to meet the operculum posteriorly.  The suboperculum  of Scaumenacia is nearly g the size of the operculum, the largest suboperculum in the superorder. Relationships;  The close correspondence of a l l the branchiostegal  series to Dipterus leaves l i t t l e doubt that i t is related to the Dipteridae.  It may be distinguished by i t s larger suboperculum and the  presence of only one accessory branchiostegal. Reference;  Stensio (1947). ^ Fleurantiidae  Branchiostegals;  Not preserved.  60  Gular3:  In f i g . 3 of Fleurantia in Graham-Smith and Westoll, are bones  which apparently represent a large oval posterior paired gular and a branchiostegal (or suboperculum ?).  A paired gular in another specimen  bears an arc-shaped pit l i n e . Operculars:  Operculum large and pentagonal,  Hyoid arch:  Ceratohyal short, stout, hour-glass shaped and much  expanded at the posterior end, only slightly anteriorly. Relationships:  Poorneas of preservation of the branchiostegals enables  l i t t l e to be deduced from them.  Graham-Smith and Westoll believe  Fleurantia to be a secondary development from the normal dipnoan ancestor, such as Dipjterus, Scaumenacia being more advanced in fin structure. References:  Graham-Smith and Westoll (1937). ^ ORDER URONEMIFORMES  Branchiostegals and gulars not known; a large oval operculum and a small elongate suboperculum present; ceratohyal known. Lower Carboniferous to Upper Permian. Taxonomy:  Two families.  Romer does not distinguish the Uronemidae from the Dipteridae.  Arambourg and Guibe synonymize the Conchopomidae with the Uronemidae and the Uronemiformes with the Ctenodontiformes. provisionally retained here.  Berg»s classification  is  61 ^ Uronemidae Branchiostegals: Gulars;  Not known.  Not known.  Operculars;  A large oval operculum is found in Uronemus splendens.  has a small dorsal projection.  It  A small bone figured below may represent  a suboperculum. Hyoid arch:  Bones resembling the centre portion of ceratohyals have  been illustrated. References:  Watson and G i l l (1923), Woodward (1891). / ' Conchopomidae  Branchiostegals: Gulars:  Not known.  Not known.  Operculars: is known.  In Conchopoma gadiformis a large oval vertical operculum It bears a small dorsal projection.  A small angulated wing-  like bone may represent a suboperculum. Hyoid arch:  The ceratohyal is of even breadth anteriorly, but is much  expanded posteriorly. References:  Watson and G i l l (1923). /  ORDER CTEMODONTIFORMES  Branchiostegals not known; one pair of gular plates known; large scallop-shaped operculum; small elongate suboperculum.  Lower Carboniferous  62 to Lower Triassic.  One family. /  Ctenodontidae PI.  Branchiostegals: Gulars;  II  Mot known.  A pair of crescentic gular plates situated anteriorly in the  fork between mandibular ramii is described for Sagenodus.  Mesial flanges  projecting from these look as i f designed to support a pair of gulars posteriorly. Operculars;  Operculum present in Ctenodus and Sagenodus.  It is large,  roughly circular, scallop-shaped, and bears, where i t inserts, a curved depression dorsally.  On i t s antero-ventral border l i e s a small elongate  suboperculum; a ridge runs along i t s length externally. Relationships:  Except for a dorsal evacuation the operculum of  Sagenodus much resembles that of Dipterus.  The anterior pair of gular  plates i s , however, of quite different conformation from that of Dipterus, being more cresentic. References;  Woodward (1891), Watson and G i l l (1923). SUPERORDER CERATODI  Gular plates and branchiostegals absent.  Operculum reduced to an  elongate ray which rests on the supratemporal-intertemporal The slender suboperculum rests on the ceratohyal. sometimes hypohyal present. Carboniferous to present.  (squamosal).  Ceratohyal and  Interhyal absent except in larvae. Two orders.  Upper  63 Taxonomy:  Arambourg and Guibe (1958) synonymize, without discussion,  the Lepidosirenformes with the Ceratodiformes.  These two orders are  retained here; hyoid arch differences support their separation. ORDER CERATODIFORMES A reduced operculum and suboperculum present; hypohyal, ceratohyal (expanded greatly at the upper end) and interhyal present in larvae. Upper Carboniferous to present.  One family which includes a living  representative Neoceratodus forsteri in Australia. Ceratodidae P l . II Operculars:  In Neoceratodus operculum reduced in size and  an arrow head pointing posteriorly.  3 h a p e d  like  The elongate oval suboperculum  inserts on the expanded distal end of the ceratohyal. end of the suboperculum is an oval cartilaginous plate.  Under the distal G i l l opening  restricted to side of head. Hyoid arch:  Composed of a small rectangular cartilaginous hypohyal and  a large ossified ceratohyal.  The ceratohyal is shaped as in Conchopomidae,  that is of even breadth anteriorly and expanding greatly at i t s posterior end.  Figures in Gregory, Goodrich and Holmgren and Stensio show no  other hyoid bones (except a small cartilaginous hyomandibular).  De Beer  shows three bones, the "stylohyal", the ceratohyal and the hypohyal in a larval specimen.  In the adult specimen here examined only a ceratohyal  was present; the cartilaginous hypohyal, i f present, was shrivelled and there was no sign of an interhyal.  64 References:  Ridewood (1894)# Gregory (1951), Holmgren and Stensio  (1936), Goodrich (1958), de Beer (1937). Material examined:  Neoceratodus forsteri, skeletal specimen,  uncatalogued NIC, Queensland, Australia. ORDER LEPIDOSIRENIFORMES Operculum and chevron-shaped suboperculum reduced to a slender ray; only the ceratohyal (slightly expanded at the upper end) present in hyoid arch.  Two families, Lepidosirenidae with a single l i v i n g species  in Brazil and Protopteridae with four living species i n Africa; both in freshwater. Taxonomy:  Upper Carboniferous to present. Arambourg and Guibe (1958) synonymize Protopteridae with  Lepidosirenidae and Lepidosireniformes with Ceratodiformes.  These groups  are provisionally retained following Berg's classification. Lepidosirenidae PI. II Operculars:  Operculum reduced to an elongate flat ray bearing a small  cartilage under i t s distal tip in Lepidosiren.  It inserts on the supra-  temporal- intertemporal (squamosal), the hyomandibular being absent. The suboperculum i s shorter but wider than the operculum.  The suboperculum  i s a chevron-shaped bone which inserts on the upper ceratohyal. underlain by a broader cartilaginous base.  It i s  This base i s called an  interoperculum by Bridge, but i t can hardly be that bone which unknown in the dipneustians (found only in the more advanced Actinopterygii). Nor are the cartilaginous distal tips of the operculum and suboperculum  65 l i k e l y to be a remnants of a hyoid ray, as he suggests, but are rather unossified portions of the operculum and suboperculum.  G i l l opening  restricted to side of head. Hyoid arch:  Only a ceratohyal is present (even embryologically), the  hypohyal, interhyal and hyomandibular being absent.  The ceratohyal is  large, bowed slightly downwards and expanded slightly at each end.  It  is attached to the parasphenoid by a ligament (the hyomandibular wanting).  There is an odd patch of cartilage on the outer surface of  the distal portion of the ceratohyal. Relationships:  The reduced operculum and ceratohyal with posterior end  unexpanded of the Lepidosireniformes are doubtless derived from the less reduced operculum and ceratohyal with expanded posterior end of the Ceratodiformes.  That is the Ceratodiformes are more primitive than the  Lepido sireniforme s. References:  Gregory (1951), Ridewood (1894), Bridge (1898), Holmgren  and Stensio (1936), de Beer (1937). Material examined:  None. Protopteridae  Operculars:  The operculum tapers posteriorly to a point in Protopterus;  i t appears to insert on the supratemporal-intertemporal (squamosal). The operculum bears an inner cartilage as in Neoceratodus.  The sub-  operculum is essentially similar to that in Lepidosiren. being an elongate chevron-shaped bone over a cartilaginous base.  It inserts on  66  the posterior* end of the ceratohyal.  G i l l opening restricted to side  of head. Hyoid arch:  Only a ceratohyal is present, the basihyal, hypohyal,  interhyal and hyomandibular are lacking. slightly expanded at each end.  The ceratohyal is large and  There is a patch of cartilage on the  outer surface of the anterior end of the ceratohyal.  This i s called a  vestigial hyoidean ray by Bridge, but i t s position does not confirm this suggestion.  Ligaments connect the ceratohyal to the skull and to  the lower jaw, as in Lepidosiren. Relationship:  The correspondence of the operculars and ceratohyal in  Lepidosirenidae and Protopteridae suggest they are closely related. References:  Ridewood (1894). Bridge (1898), Dean (1895).  Material examined:  None.  67 SUBCLASS BRACHIOPTERYGII ORDER P0LYPTERIF0RME3 Branchiostegals absent; median gular absent; a very large pair of lateral gulars (longer than 2/3 of mandible length); large operculum; small suboperculum present - or absent; interoperculum absent. Tertiary (Eocene) to present.  A single order and family.  Lower  It is the  only actinopterygian derived group with lateral gulars and lacking branchiostegals. Polypteridae PI. IV Branchio3tegal3: Gulars:  Absent.  Median gular absent.  A pair of large lateral gulars which  extend from the symphysis to slightly past the posterior end of the mandibles, extending to the midventral line to a point just before the posterior end of mandibles.  A short transverse pit line in the form of  an arc is found near the middle of each.  According to Daget (1958) the  gular pit line is innervated by a nerve extending posteriorly from middle of the ramus mandibularis f a c i a l i s .  the  In Calamoichthys the gulars  are slightly shorter, and the tip of the right overlaps the tip of the left.  The large gular plates are reminiscent of those in Crossopterygii.  Operculars:  Operculum oval and larger than the triangular suboperculum,  in Polypterus.  Subopercle absent in Calamoichthys.  separate, with right over l e f t .  G i l l membranes  68  Hyoid arch:  A partially ossified hypohyal-, a ceratohyal and interhyal  are present. Taxonomy:  The ends of the ceratohyal and interhyal are not ossified.  The family Polypteridae consists of two living African  freshwater genera Polypterus and Calamoichthys (Relationships:  lirpetoichthys).  The absence of an interoperculum relates i t to the  lower Actinopterygii.  The enlarged lateral gulars recall those of  Pyritocephalus and Haplolepis (Haplolepiformes).  These forms also have  pit lines on the lateral gulars, the branchiostegals reduced and the operculum larger than the suboperculum.  The similarity of the lateral  gulars to the Crossopterygii and Dipnoi is doubtless a parallelism. The lateral gulars expanded to cover the region exposed by the loss of the branchiostegals. Evidence on i t s relations also comes from i t s sensory lines (Stensio, type.  1 9 4 7 ) .  The sensory line of the cheek is of the actinopterygian  In i t s principal features i t i s much as in advanced lox*er ganoids,  but in some respects i t has reached the stage of holostean ganoids.  The  postmaxillary line is similar in i t s connection with the dermal bones to lower ganoids and parasemionotids. sub-holostean ancestor (Stensio, References:  Devilliers  Material examined: Nigeria.  ( 1 9 5 8 ) ,  They are probably derived from some 1 9 4 7 ) *  Daget  ( 1 9 5 8 ) ,  Allis  ( 1 9 2 2 ) ,  Berg  Calamoichthys sp., alcoholic specimen, ROM  ( 1 9 4 7 ) .  1 8 8 7 7 ,  69  SUBCLASS ACTINOPTERYGII Branchiostegals 0 - 5 0 ; median gular present or absent, primitively with a V-shaped pit line; lateral gulars, i f present, with length less than one half of mandible length; operculum and suboperculum usually present; in higher forms interoperculum usually present; interhyal, epihyal (in higher forms), ceratohyal and hypohyal(s) usually present. Lower Devonian to present.  Five supraordinal groups with 56 orders 34  of which are l i v i n g . It has been made apparent by various authors, Stensio, Berg, Schaeffer, Gardiner, etc., that the Chondrostei, Holostei and Teleostei (as constituted) are not natural groups, that the Holostei are polyphyletic and that some of the characters which have been used to distinguish the Holostei occur in certain chondrosteans.  This has been  interpreted as meaning that the Chondrostei, Holostei and Teleostei are not valid groups. However, other interpretations are possible. orders have been placed in the wrong group.  F i r s t l y , that some  Secondly, that some of the  characters previously used to define the groups have not been diagnostic, although they may tend to be more frequent in one group than the other. According to this interpretation the groups, i f reconstituted and redefined, would be natural. The interoperculum i s an important character in diagnosing the Holostei.  It i s absent in the Chondrostei, present in the Holostei and  present in the Teleostei (except in a few groups of the latter where i t is secondarily l o s t ) .  One group presently placed in the Holostei, the  Lepisosteiformes lacks and interoperculum, but has a maxillary free from  70  the cheek.  However, the jaws have moved far forward, decreasing the  need for an interoperculum and the preoperculum has expanded ventrally supplanting the position normally occupied by one.  It may safely be  suggested therefore that the interoperculum has been secondarily l o s t . The Platysiagiformes have been suggested to bear an incipient interoperculum.  This has been demonstrated not to be so.  Further, i t  bears a maxillary fixed to the cheek and clearly belongs in the Chondrostei.  Brough (1939) considered that the maxilla of the  subholostean Luganoia was free, but his figure 15 shows the end of the maxilla snugly fitted against the large plate-like preoperculumj i n other figures i t appears displaced from this notch. maxilla was not free. in the Chondrostei.  It is concluded the  This and the lack of an interoperculum places i t The Ospiiformes have been considered chondrosteans  but their maxillary is free and i t i s now clear that they possess an interoperculum (Stensio, 1932; Lehman, 1952).  There now appears to be  no good reason not to place the Ospiiformes in the Holostei.  The  Pycnodontiformes lack an interoperculum and yet have been placed in the Holostei.  But recent authors (Rayner, 1941 and Gardiner, I960) and the  present author are in agreement as to their placement in the chondrosteans near the platysomoids or boba3atraniiforms. When the above changes have been made the Chondrostei and the Holostei comprise homogeneous groups.  A l l of the Holostei have a free  maxillary and an interoperculum (except that the interoperculum is lost in the Lepisosteiformes) and-all of the Chondrostei have a fixed maxillary (except Dorypterus where the maxillary has shortened and become secondarily free) and lack an interoperculum.  That there are  71 other characters which would support this grouping is suggested by Schaeffer's fine association analysis of differential characters.  It  is also certain that some characters, previously employed to characterize the groups (such as the relation of rays to their supports) do not definitively separate the two groups (however i t might s t i l l be possible to state that in chondrosteans fin rays exceed or equal pterygiophores and in holostei equal pterygiophores). The Teleosti may be separated from the Chondrostei and Holostei by the lack of lepidosteid tubules either in their scales or skeleton, and the primitive presence of intermuscular bones and two hypohyals. For the above reasons the modified supraordinal groups Chondrostei (Group I), Holostei (Group l l ) and Teleostei (Group III) are therefore reinstated.  The Teleostei are further subdivided into the Malacopterygii  (Group IIIA) and the Acanthopterygii (Group IIIB).  The group Mesichthyes  is discarded, a 3 w i l l be discussed later. GROUP I . Without interoperculum. single hypohyal.  CHONDROSTEI  Lateral gulars present or absent.  A  Lower Devonian to Present.  /. ORDER PALAEONISCIPORMES (AEDUELLIFORMES, GYMONISCIFORMES) Branchiostegals (1)4-23, spathiform; median and a pair of lateral gulars; operculum and suboperculum present, interoperculum absent; interhyal, epihyal, ceratohyal and a hypohyal known. Lower Cretaceous.  Lower Devonian to  Several families.  Following Lehman (1958), Berg s Gymnonisciform.es are included in f  the Palaeonisciformes.  The Palaeonisciformes are a diverse group which  72 w i l l probably be broken up into other orders when a detailed taxonomic revision i s made.  However, the practice of removing poorly known  families from Palaeonisciformes and raising them to ordinal status does not seem advisable. SUBORDER PALAEONISCOIDEI / Cheirolepidae PI. I l l Branchiostegals:  11-13 branchiostegals are found in Cheirolepis; these  are short, wide and spathiform. Gulars:  A median gular has not previously been reported in this group.  In Traquair's (I675) figure of the ventral view of the jaws a diamondshaped, bilaterally symmetrical bone i s seen overlying the lateral gular of the right side. median gular.  It seems l i k e l y that this element i s a displaced  As median gulars are found in other Palaeonisciformes,  dipnoans and coelacanth3 i t would not be surprising to find one in Cheirolepis.  A pair of wide lateral triangular gulars each with a pit  line are found next to the last branchiostegal. Operculars:  Operculum inclined forwards and much longer than the  suboperculum. Relationship:  The branchiostegals and opercular bones of Cheirolepis  are l i t t l e different from those of the palaeoniscid, Glaucolepis*, most other characters are in accord with this.  The small scales, as pointed  out by Aldinger (1937) are however, very similar to those of acanthodians.  Cheirolepis thus forms a connecting link between the  73 Teleostomi and Acanthodii. References:  Traquair (1875), Watson (1925), Woodward (1898), Lehman  (1947). ^ Palaeoniscidae Pl. I l l Branchiostegals: spathiform.  (l) 4 - 2 3 usually 9-15 branchiostegals, short, wide and  In Glaucolepis at least, the last 5 branchiostegals insert  on the ceratohyal, none on the hypohyal; presumably rays also seat on the epihyal (see Nielsen s excellent photo p l . 1 1 and 1 6 , 1942). T  Palaeoniscus 8-9, Oxygnathus 12, Gonatodus 10, Boreosomus 7-8, Hyllingea 2 3 , Ple/^molepis ca. 16, Watsonichthys 15, Acrolepis 1 4 , Diaphorognathus 7-9, Pygopteru3 20, Pteronisculus  12-22,  13-15, Cornuboniscu3 16, Rhadinichthys  Stegotrachelus 6, Glaucolepis  10-11,  Cycloptychius 10, Canobius  4 - 6 , Me30poma 5-7, Nematoptychius 20, Aeduella 1 . Gulars:  A median gular is known from most forms which are sufficiently  preserved to show i t 3 presence. the gular region.  In Hyllingea only scales are found in  In some forms a second gular is found, a small anterior  gular near the symphysis overlying a larger median gular which projects posteriorly to the branchiostegals; in these the lateral gulars are absent (Bbreosomus, Diaphrognathus).  In most other adequately  represented forms a pair of small lateral gulars is present (Pteronisculus, Palaeoniscus, Gonatodus etc.). gular with V-shaped pit l i n e i  In Aeduella is a large diamond-shaped The adjacent "branchiostegal" is  identifiable a 3 a lateral gular by the arc-shaped pit l i n e .  These occupy  74 less than a quarter or third of the length of the mandibles. Operculars;  Operculum and suboperculum present, the operculum generally  larger and inclined forwards, except in the short-jawed forms. Hyoid arch:  Watson (1925) did not find an ossified epihyal in any  palaeoniscid.  He described a short hypohyal and a long ceratohyal in  Elonichthys.  A hypohyal, long ceratohyal and short element (called 2nd  ceratohyal (=epihyal, separate ceratohyal ?) by Nielsen, (1942) are evident in Glaucolepis.  The ceratohyal and this element bear a lateral  groove for the afferent hyoid arteries.  Acrorhabdus is known to have a  long hourglass-shaped ceratohyal and a triangular epihyal (?) (shaped similarly to the epihyal in higher forms such as Salvelinus); another bone, possibly the interhyal i s present. Taxonomy:  Palaeoniscidae i s here used in the sense of Berg (1947) and  includes the families Thrissonotidae (Oxygnathidae), Rhadinichthyidae, Canobiidae, Elonichthyidae, Pygopteridae, Acrolepidae, Amblypteridae, Scanilepidae, Dicellopygidae, Boreolepidae, Cocconiscidae, Cornuboniscidae, Tegeolepidae, Styracopteridae, Aeduellidae (the latter raised to ordinal status in a classification outline in Traite de Zoologie, v o l . XIII, fasc.  3, 1 9 5 8 ) .  Gymnoniscidae (Gymnonisciformes of Berg) is included in  Palaeoniscidae following Lehman (1958); Westoll (1944) believed i t to be only the young of Sceletophorus, a palaeoniscid. Berg's lumping of so many diverse forms into the family Palaeoniscidae does not seem reasonable.  Perhaps Rorner's recognition  of many families would be more acceptable, although he f a i l s to segregate  75  any of the lower Chondrostei into orders.  However, the author did not  feel in a position to accept a l l of these families, many monotypic, without analysis,  Nielsen (1949) felt that Aldinger had gone somewhat  too far in subdivision of the old palaeonisciid group.  Berg's  classification was therefore provisionally followed, rather than inadvisedly raising groups to family status. In looking at the variation of the branchiostegal series in a few of the many known paleoniscids, family recognition of certain forms seem to be suggested.  Proper delimitation into families w i l l of course  require examination of a l l forms and looking at more than one set of characters.  The two median gulars of Boreosomus and Diaphrognathus set  them well aside from other palaeoniscids.  Several forms have sufficiently  numerous branchiostegals to separate them from other palaeoniscids: Agecocephalus, Hyllingea, Nematophychius and Pygopterus have 20 or more branchiostegals.  On the other hand the few highly curved branchiostegals  in Canobius and Mesopoma would seem partly to justify the family Canobiidae,  Aeduella is distinct in having only a single branchiostegal.  Although most of the other genera examined are united in having a median gular, a pair of lateral gulars, and 9 to 15 branchiostegals, family delimitation on other bases is of course possible. References:  Berg (1947, 1955), Nielsen (1942), Moy-Thomas and Dyne  (1937), Aldinger (1937), Woodward (1091), Woodward and White (1926), Lehman (1958), Brough (1933), White (1933), Gregory (1951), White (1939).  76 yf ' Coccolepidae Branchiostegals:  About 14 in Coccolepis macropterus.  The branchiostegals  are short, spathiform and slightly curved, s:ijrdlar to those of palaeoniscids. Reference:  Berg (1947). ^ Birgeriidae  Branchiostegals:  About 14 in Birgeria.  These are of medium length and  spathiform. Gulars:  A small oval median gular and a pair of small lateral gulars  which are almost identical to the adjacent branchiostegals were found. P i t lines absent. Operculars:  The opercular  bone3  are separated.  The operculum is  horizontal and oval; the suboperculum consists of 4 to 6 vertical triangular rays which are fused ventrally, a unique feature in the Palaeonisciformes. Hyoid arch: Taxonomy:  A long ceratohyal and a short hypohyal are known. Birgeria may be a synonym of Xenestes; this, according to  present rules, need not result in a change of the family name. Relationships:  The unique, fan-like subopercle distinguishes  family from other palaeonisciforms.  this  The branchiostegals and gulars are  consistent with a palaeoniscid derivation.  Mielsen (1949) believed the  body skeleton and dermal bones of the head point to a f a i r l y close  relationship to the Palaeoniscidae.  V/atoon (1925), Stensio (1932) and  Aldinger (1937) believed the chondrocranium, spiracle, position of nostril and reduced endoskeleton indicate an approach to the sturgeons. References:  Nielsen (1942)* ^ Holuridae  Branchiostegals:  12 in Holurus parki, 8 in Holuropsis yavorskii, these  short, spathiform with lower edge curved. Operculars:  Operculum and suboperculum present, rectangular.  References:  Moy-Thomas (1937), Berg (1955). ^ Urosthenidae  Branchiostegals:  Head not known.  Lehman (1958) would reduce this  family to a subfamily of Palaeoniscidae. References:  Berg (1947, 1955). ^ Turseoidae  Branchiostegals:  6-7 in Gwynoddichtis.  Wide, slightly curved spathiform  rays. Gulars:  The small median gular is considerably behind the symphysis and  sits on top of the lateral gulars.  The lateral gulars extend to the  symphysis. Operculars: suboperculum.  Operculum a slender rectangle longer than the trapezoidal  78 Relationship;  The Turseoidae differ from the palaeoniscids in the  arrangement of the gular plates and in the reduced number of branchiostegals, but not so highly as to preclude immediate derivation from them. References:  Bock (1959). SUBORDER PLATISOMOIDEI  Although platysomoids tend to have fewer branchiostegals and more vertical operculars than the palaeoniscoids, both of these characters overlap.  The two characters seem to be associated with a shortening of  the jaws, requiring fewer branchiostegals to cover the throat and with erecting the suspension, making the operculars more vertical.  They are  doubtless palaeoniscoid derivatives, / Platysomidae Branchiostegals:  6-7 in Platysomus, about 4 in Paramesolepis tuberculata.  Wide, spathiform, with ventral edge curved upwards. Operculars:  Operculum and suboperculum are vertical and about equal in  size. References:  Lehman (1958), Moy-Thomas and Dyne (1937), Woodward (1898). ^ Amphicentridae  Branchiostegals:  About 5 in Cheirodopsis, 6 in Eurynotus geikei, about  7-9 in Amphicentrum, elongate, spathiform, widening distally, ventral edge straight.  79  Operculars:  Operculum and suboperculum high, and oval or rectangular,  about equal in References:  3ize  and vertically oriented.  Lehman (195G), Woodward (l«9l), Homer (1955), Dyne (1939). f ORDER TARRASIIF0RME3  Branchiostegals 15, spathiform; gulars not known; operculum and suboperculum present, interoperculum absent.  Lower Carboniferous. A  single family. ^ Tarrasiidae PI. I l l Branchiostegals:  1 5 in Tarrasius problematicus.  Spathiform, lower edge  curving upward, upper ones elongate, lower short. Gulars:  Text and figures make no mention of gulars.  The anterior  branchiostegal is figured as broader and may possibly represent a lateral gular. Operculars:  Operculum and interoperculum subrectangular and horizontally  oriented. Relationships:  Tarra3iu3 differs from most palaeonisciforms in the  opercle and subopercle being long horizontally and the operculum not being greatly inclined forwards.  Unlike other short-jawed forms the  number of branchiostegals has not been reduced but they have been bunched closely together.  The shortening of the jaws may be associated  with the durophagus habit indicated by the teeth.  The number and form  of the branchiostegals are not out of line with a palaeonisciform  80  derivation.  According to Moy-Thomas, "Tarrasins problematicus is  certainly a Palaeoniscid, as shown by the characteristic arrangement of the bones of the skull, axial skeleton, supporting the skeleton of the median fins and microscopic structure of the scales.  It i s however,  specialized in having continuous dorsal and ventral fins, and a diphycercal t a i l , loss of scales on the main body and shagreen-like scales on the caudal region, the peculiar shape of the pectoral, and loss of the pelvic fins".  One might add to these specializations the  elongate, blenny-like form. References:  Traquair (1881), Moy-Thomas (1934). ^ ORDER PHANER0RHYNCHIF0R11ES  A long series of branchiostegals; gulars not known; operculum and suboperculum present; interoperculum absent.  Middle Carboniferous. A  single family. ^ Phanerorhynchidae Branchiostegals:  Phanerorhynchus i s described as having a long series  of branchiostegals.  The two branchiostegals depicted appear narrow,  pointed and quite small. Gulars:  It wa3 impossible to 3ee whether lateral or median gulars were  present in the specimen. Operculars:  A long and slightly oblique operculum with sparse  longitudinal ridges and a small subopercular present.  Taxonomy;  Romer (1955) places Phanerorhynchus in the Haplolepidae,  apparently on the basis of the scales.  But Phanerorhynchus is quite  different from Haplolepidae in the possession of a long sturgeon-like snout.  Westoll (1944) in a revision of the Haplolepidae states that  Haplolepis is sharply distinct from Phanerorhynchus and that the possession of deep flank scales by these two groups i 3 most feasibly regarded as parallelism.  Phanerorhynchus is thus here placed in i t s  own order, as in Berg. Relationships;  The branchiostegal series are too poorly known to shed  light on relationships.  G i l l and Watson believed the skull and shoulder  girdle showed conclusive evidence of palaeoniscid affinities,  but the  build, character of the caudal peduncle, short-based pelvics, few large dermal rays in the fins and long undivided rostral bone were distinctive. Stensio (1932) placed i t in the vicinity of Saurichthyidae.  But as Berg  (1947) noted the Phanerorhynchidae are so specialized as regards to fin structure that they cannot be regarded as ancestors either of Saurichthyidae or Acipenseridae.  It thus seems preferable to regard  them as an independently evolved sturgeon-like form derived from the P alaeonisc iforme s. References;  G i l l and Watson (1923), Stensio (1932). / ORDER HAPLOLEPTFORMES  Branchiostegals 1-3 spathiform, the one next to the lateral gular expanded; large median and la'teral gulars; V-shaped pit line on median gular; opercle and subopercle present; interoperculum absent. Carboniferous.  A single family.  Upper  82  ^ Haplolepidae PI. I l l Branchiostegals:  1-3 in Haplolepis; 1 in Pyritocephalus.  The  branchiostegal behind the lateral gular (present in a l l forms) is large, rectangular or triangular and may be as large as one third of the size of the lateral gulars.  The second and third branchiostegals, when  present, are very broad with rectilinear edges. the branchiostegals is very short.  The exposed portion of  In Pyritoc ephalus there i s a gap  between the single branchiostegal and the suboperculum. Gulars:  A large median gular 1/3 - h the length of the mandible is  present; i t bears a V-shaped p i t line with the apex facing posteriorly. A large pair of lateral gulars occupy about 1/3 the length of the jaws. A short transverse pit line i s found in the middle of each lateral gular. The enlarged anterior branchiostegal, referred to in the literature as a posterior paired gular, i s here considered a branchiostegal. Operculars:  Either the operculum or the suboperculum may be larger.  These are vertically oriented in this small-jawed form. Taxonomy:  After Westoll's thorough revision of the family, Lehman  raised i t to ordinal status. Relationships:  The short jaws, vertically oriented operculars and few  branchiostegals in the Haplolepidae remind one of Catopterus and Mesopoma, although the large median and lateral gulars of Haplolepidae do not appear to be present in these forms.  However, the similarities  in operculars and branchiostegal rays may not be an indication of close  03 common ancestry, but only parallel evolution following a reduction in jaw length.  The large size of the gulars and the few branchiostegals  distinguish the Haplolepidae from the palaeoniscids, perhaps at the ordinal level, although i t i s , no doubt, derived from them. References:  Westoll  (1944),  Lehman  (1958).  / ORDER REDFIELDIIFORMES One large spathiform branchiostegal (sometimes split) below the suboperculum, perhaps absent in some; gulars absent; opercle and subopercle present; interoperculum absent. single family.  Following Lehman  (1958)  Lower to Upper Triassic. A Brookvaliidae is synonymized  with Redfieldiidae. ^ Redfieldiidae Pl. V Branchiostegals:  1 large trapezoidal branchiostegal (called infraoperculum  by some authors) below the subopercle in Brookvalia; a triangular one in Geitichthys, Atopocephala, Helichthys and Phylctaenichthys.  In  Daedalichthys is a curious oval plate (overlying the suboperculum) which is divided into two by a horizontal joint, the lower part larger. Doubtless the plate represents a single split branchiostegal. on the other hand, according to the figure in Berg  (1955),  Redfieldius  has a longer  suboperculum and lacks a branchiostegal. The term infraoperculum i s equivalent to the branchioperculura of Hubbs; both refer to an enlarged uppermost branchiostegal. Gulars:  A small narrow median bone may represent a gular in Brookvalia.  84  Gular plates do not appear to be present in other genera. Opercular bones:  Opercle and subopercle approximately equal, sub-  quadrangular, almost vertical. Taxonomy:  Catopteridae was f i r s t applied to the family in 1890.  In  1899 Hay discovered Catopterus Redfield 1837 was a junior homonym of Catopteru3 Agassiz 1833.  Hay proposed a replacement name, Redfieldius  for Catopteru3 Redfield.  Then he proposed a new family name  Dictopygidae, based on Dictopyge (a genus in the same family) to replace Catopteridae.  But, according to Article 39a of the International Code  of Zool. Nomenclature, the f amily name must be changed to one based on the valid name of the original nominal type-genus, in order to preserve the taxonomic concept.  That i s , the new family name must be based on  the substitute name Redfieldiu3 (there being no junior synonyms available), rather than on another genus in the same family, Dictopyge. Berg was therefore correct in applying Redfieldiidae and Redfieldiiformes to this group and the name Dictopygidae is therefore a junior subjective synonym.  Catopteridae has been used by most authors for this family:  Stensio (1921, 1932), Wade (1935), Brough (1934), and Lehman (1958), although Romer (1955) used Dictopygidae.  Most of these authors were  apparently unaware of the homonymy of Catopterus.  The last section of  Article 39 ("The provisions of this section are not to be applied so as to upset a widely accepted family-group name that was established before 1961 under a different procedure") does not apply to Catopteridae although i t might have applied to Dictopygidae had i t been widely accepted.  So Redfieldiidae and Redfieldiiformes are the proper familial  and ordinal names for this group.  85 Relationships:  Lehman (1958) considered the Perleidae and Catopteridae  quite close, differing principally i n dentition and fin anatomy. He therefore synonymized the two orders employed for them by Berg under Perleidiformes.  The present study shows the branchiostegals of Bergs  two order3 differ markedly. branchiostegal. branchiostegals.  In Redfieldiiformes there i o one broad  In Perleidiformes on the other hand there are 7-12 Gular3 are unknown in Redfieldiiformes, median and  lateral gulars are found in Perliediformes.  Brough (1931) presents a  table giving 9 differences but Schaeffer (1955) indicates that only two of these, excess of rays over radials and the number of branchiostegals are consistent and taxonomically important. The dilated branchiostegals of Redfieldiiformes are suggestive of those in Haplolepidae, which also has very few branchiostegals (one to three).  Haplolepidae differ in the possession of large well developed  lateral and median gulars. References:  Berg (1955), Wade (1935), Brough (1931* 1934). / ORDER PERLEIDIFORMES  Branchiostegals 7-12, spathiform; a median gular with a V-shaped pit line and a pair of lateral gulars; operculum and suboperculum present; interoperculum absent; ceratohyal known. Upper Triassic.  Lower Triassic to  A single family.  Teleopterina (=Pyritocephalus) i s included in the Haplolepidae following Westoll (1944). following Lehman (1958).  Cleithrolepidae is included in the Perleidae  86 J 1  Perleidae Pl. I l l  Branchiostegals:  7 broad spathiform i n P e r l e i d u s (not i n c l u d i n g the  lateral gular); 10 narrow spathiform i n M e r i d e n s i a ; 1 2 narrow spathiform in  Cleithrolepis and Colobodus; at l e a s t 2 or 3 i n the fragmentary  specimen of Manlietta.  On the left, but not the right side, of Lehman's  figure of Perleidus madagascariensis is a small branchiostegal half the length of the others; presumably this is teratological. Gulars:  An oval or diamond-shaped median gular of moderate size is  present.  In Perleidus i t bears a V-shaped pit line, v/ith the apex  facing posteriorly.  The median gular of Manlietta i s very large, about  as long as the mandible.  The lateral gulars are identical in form to  the adjacent branchiostegals, which are short and wide in Perleidus; but the lateral gulars bear pit lines. Operculars:  Suboperculum larger than the operculum.  These are not deep.  Hyoid arch:  In Perleidus the ceratohyal is short aid expanded at both  ends in the usual hourglass-shape. Relationships:  Differences between this order and Redfieldiiformes are  discussed under the latter order.  Wade (1935) indicates that  Cleithrolepis is probably derived from the platysomids.  However, the  more numerous branchiostegals of Cleithrolepis cast doubt on this view. The  V-shaped pit lines on the median gulars of Haplolepiformes aid  Perleidiformes would seem to indicate a common ancestory, probably from the Palaeonisciformes.  Because of the more numerous branchiostegals of  87  Fer-leidiformes i t is unlikely that they were directly derived from the Haplolepiformes.  The sensory canal system i s very close to that of  Glaucolepis (Palaeoniscoidei) References:  (Lehman 1952).  Lehman (1952), Brough (1939), Wade (1935), Stensio (1921),  Schaeffer (1955). ^ ORDER DORYPTERIFORMES Branchiostegals absent; gulars absent; operculum, suboperculum and interoperculum absent.  Upper Permian. A single family. ^ Dorypteridae PI. V  Branchiostegals: Gulars:  Absent.  Absent.  Operculars:  Absent, although a small bone has been tentatively identified  as an operculum in one specimen. Hyoid arch:  A long rectangular bone has been termed the ceratohyal but  Westoll suggests that i t i s an ectopterygoid. Relationships:  The reduction in the branchiostegal series suggests  derivation from the Platysomoidei rather than the Palaeoniscoidei. Westoll believed only the Platysomidae could have given rise to them. Lehman (1958) places the order in the family Platysomidae.  While i t is  possible that Dorypterus should not be ordinally separated from the platystomids i t requires at least familial separation on the basis of:  m absence of branchiostegals, absence of scales on a l l but the abdomen, the skull being roofed by a single bone aid the well developed ventrals. Further, Westoll states that G i l l ' s recognition of i t 3 remarkable specialization can only be more strongly endorsed.  In the relation of  the number of fin rays to pterygiophores Dorypterus is intermediate between platysomids and Bobasatrania according to Stensio ( 1 9 3 2 ) .  The  order Dorypteriformes i s thus provisionally retained. References:  Berg ( 1 9 4 7 ) , Stensio ( 1 9 3 2 ) , G i l l ( 1 9 2 5 ) , Westoll ( 1 9 4 1 ) . ^ ORDER BOBASATRANIIFORMES  Branchiostegals, i f present, 1-2 or to 4; gulars unknown; operculum present; suboperculum and interoperculum absent.  Lower Triassic. A  single family. ^ Bobasatraniidae Pl. V Branchiostegals:  One or two, i f present; in some, oval or quadrate in  shape, in others there appears to be traces of at least 4 elongate spathiform branchiostegals. Gulars: Unknown. Operculars:  A small narrow operculum present.  Suboperculum absent;  appears to have coalesced with the lower preopercular plate. Hyoid arch:  A small hourglass-shaped ceratohyal.  Relationships:  In the reduction of the branchiostegal series  Bobasatraniiformes would appear to be related to but not immediately  89  derived, from the Dorypteriformes.  They probably share a derivation from  the platysomoids (Stensio, Westoll). Referencesi  Berg (1947), Stensio (1932), Lehman (1958), Lambe (1914),  Westoll (1941). f ORDER PYCN0D0MTIF0RME3 Branchiostegals at least 2-5, acinaciform or spathiform; gulars absent; elongate vertical operculum; suboperculum replaced by preoperculum; interoperculum absent. Relationships;  Upper Triassic to Eocene.  Three families.  The phylogenetic position of this order has been  something of an enigma.  Berg and Romer place i t among the holosteans,  Arambroug and Bertin in their enlarged order Amiiformes.  Stensio (1947),  until the question of holostean classification has been solved, provisionally retains them in the Holostei.  Gardiner (i960) derives  them, with the Bobasatraniiformes, from an offshoot of the Dorypteriformes. Rayner (1941) places them in the subholosteans and regards them as derived from the platysomids. Because of the absence of an interoperculum they are here placed in Group I.  Their skull and body structure shows similarities to the  Dorypteriformes and Bobasatraniiformes.  With them the Pycnodontiformes  share a large ventral preoperculum which replaces the suboperculum; a dorsal preoperculum; interoperculum absent; operculum elongate and vertically suspended; branchiostegals reduced; about 32-35 neural spines; vertebral centra absent; a postabdominal bone; dorsal and anals long; median f i n rays tend to equal radials; body deep.  In Gyrodus and  90 Bobnsatrania a lateral line branch runs from the skull to the dorsal origin.  However the Pycnodontiformes differ in possession of teeth and  branchiostegals and in their abdominal pelvic fins whereas in the Dorypteriformes they are thoracic.  In some Pycnondontiformes the supra-  and infra.-orbital canals join (Microdon, Eomesodon), unlike Bobasatrania. It therefore seems necessary to regard the Pycnodontiformes as an offshoot of the line which gave rise to the Dorypteriformes and Bobasatraniiformes.  This opinion is in agreement with that of Rayner  and close to that of Gardiner (i960).  Their slender curved branchiostegals,  graduating to a point, distinguish them from other orders in Group I. / Gyrodontidae Pl. V Branchiostegals:  Unknown in Macromesodon (= Mesodon).  One or two long  curved sabre-like branchiostegals under the preopercle in Mesturus. Two elongate narrow rectilinear branchiostegals in Gyrodus. Gulars:  Unknown in Macromesodon.  Absent in Mesturus where the inter-  mandibular region and throat is covered by polygonal plates. Operculars:  An elongate vertically suspended operculum in Mesturus and  Macromesodon; suboperculum replaced by large backwardly extending preoperculum.  Stensio (1947) believed the suboperculum and preoperculum  were fused and called the bone the preoperculo-suboperculum. Hyoid arch:  Poorly known but the ceratohyal is deep and a small,  hypohyal is known in Mesturus.  91 References:  Woodward ( 1 8 9 5 ) , Berg ( 1 9 4 7 ) , Arambourg and Bortin ( 1 9 5 8 ) ,  Ararabourg ( 1 9 5 4 ) , Eastman ( 1 9 1 4 ) •  / Coccodontidae Branchiostegals:  Data on branchiostegals of Coccodus has not been  found i n Woodward ( 1 8 9 5 ) or i n any other available l i t e r a t u r e .  Zittel  ( 1 8 8 7 ) reports the operculum i s large i n Zenophilus; possibly h i s operculum represents the preoperculo-suboperculum.  "f" Pycnodontidae Branchiostegals:  4 long narrow curved sabre-like branchiostegals are  apparent i n one specimen of Pycnodus (plate 72, Agassiz, 1 8 3 3 - 1 8 4 3 ) . Remains of 5 spathiform ones known i n Palaeobalistum. Gulars:  Unknown, presumably absent.  Operculars:  Operculum apparently small with ventro-posterior p r o j e c t i o n .  Preoperculo-suboperculum large as i n Gyrodontidae.  Relationships:  The available material does not i n d i c a t e great  differences between the three f a m i l i e s of the order.  Indeed Romer  includes them i n one family.  References:  Woodward ( 1 8 9 5 ) , Agassiz  (1833-43).  / ORDER PTYCHOLEPIFORI'IES Several spathiform branchiostegals; a median gular present; operculum and suboperculum present; interoperculum known.  Lower T r i a s s i c  to Lower J u r r a s i c .  absent; ceratohyal  A single family.  92 / Ptycholepidae Pl. V Branchiostegals:  Number not exactly indicated.  branchiostegal ornamented and wedge-shaped.  In Ptycholepis f i r s t  Ventral to i t there are a  series of more normal branchiostegal rays, which are moderately large and elongate, Gulars:  A large median gular present.  Operculars:  Operculum larger than the suboperculum.  Hyoid arch:  Ceratohyal i s a rather long f l a t bone somewhat constricted  in the middle. Taxonomyi  Brough demonstrated that Ptycholepis did not belong in the  Eugnathidae and placed i t in i t s own family, Ptycholepidae. Lehman (1958) raised the family to ordinal status. Relationships:  Brough places Ptycholepis in the Subholostei.  Lehman  indicates i t i s probable that Ptycholepis is a descendent of the Triassic palaeoniscid genus Boreosomus or of a genus close to Boreosomus.  The  paucity of data on the branchiostegal series prevents further suggestions being made except to 3 a y that the absence of an interoperculum precludes placement among the holostean fishes. References:  Brough (1939), Lehman (1958), Woodward (1895). / ORDER, PH0LID0PLEURIF0RJIE3  Branchiostegals 6-14, spathiform; a small median gular and a pair of large l a t e r a l gulars are known; operculum and suboperculum present;  93 interoperculum absent; hypohyal and ceratohyal known. Triassic.  Lower to Upper  A single family. ' Pholidopleuridae  Branchiostegals:  6-14.  Australosomus with 6-8 short wide branchiostegals  which become shorter and broader anteriorly; Macroaethes with 14 (19 in figure) elongate branchiostegals with curved edges and rounded tips; Arctosomus with about 12; Pholidopleurus with at least 4 (series incomplete) branchiostegals which are elongate, f a i r l y broad and resemble those in Amia.  In Australosomus the lower 3 branchiostegals and lateral  gular appear to insert on the ceratohyal. Gulars:  A small median gular in Australosomus situated anterior to the  lateral gulars. i  1 1  Australosomus.  A large triangular lateral gular triangular in outline A large triangular lateral gular in Macroaethes. A  lateral gular is not shown in the figure of Arctosomus (Berg in Nielsen, 1949).  No pit lines are found on the median or lateral gulars.  Operculars:  Operculum somewhat higher than the suboperculum in  Australosomus but equal in Macroaethes and Pholidopleurus. Hyoid arch:  In Australosomus a small curved hypohyal i s placed at the  upper anterior corner of the long compressed ceratohyal which i s grooved for the afferent hyoid artery. Taxonomy:  The few short broad branchiostegals of Australosomus appear  to differ sufficiently from those of Macroaethes and Arctosomus to suggest placement in a different family or subfamily.  94  Relationships;  Lehman (1952) criticizes the view that Australosomus  i 3 closely related to the Saurichthyidae.  Nielsen and Lehman agree  that the common characters of the two groups are those shared by most primitive palaeoniscid-type fishes.  The few branchiostegals and absence  of a suboperculum in Saurichthys indicate i t does not have close affinities \d.th Pholidopleurus.  The branchiostegal series of the  Pholidopleuriformes would seem to indicate an origin either from the Perleidiformes or from the Palaeonisciformes.  Stensio (1932) considers  i t an offshoot from primitive palaeoniscids specialized in the direction of higher ganoids and teleosts. References:  Nielsen (1949), Lehman (1952), Wade (1935). / ORDER CEPHALOXENIFORMES  Poorly known, see under description of single Upper Triassic family. / Cepaloxenidae PI. V Branchiostegals:  Unknown, the lower portion of the head not being  represented. Gulars: Unknown. Operculars;  Operculum larger than suboperculum.  Presumably no inter-  operculum. Taxonomy,:  Lehman (1958) raises Brough s family to ordinal status. T  95  Relationships:  Brough states the fins are of the holostean type, the  check bones are essentially palaeoniscid.  He places them in the  Subholostei between Platysiagidae and Peltopleuridae.  The deep flank  scales resemble those of the Luganoiidae and Peltopleuridae. References:  Brough  (1939). t ORDER AETHODONTIFORMES  Poorly known, see under description of single Upper Triassic family. / Aethodontidae Branchiostegals: Gulars:  Not preserved.  An oval median gular plate is known.  Operculars:  Lateral gulars unknown.  Operculum and suboperculum about equal in size.  Inter-  operculum presumably absent. Taxonomy:  Brough*s family was raised to ordinal status by Lehman  (1958),  although only fragmentary remains of the fish are known. Relationships:  Tne hemiheterocercal t a i l and fins with reduced rays are  subholostean in character while the cheek bones and sensory canals are palaeoniscid (supraorbital line ends on the frontal). dentition is unique among the subholostean3. References:  Brough  (1939).  The crushing  96  / ORDER LUGANOIIFORMES Poorly known, see description of the single Upper Triassic family. ^ Luganoiidae PI. V Branchiostegals: Gulars:  Unknown.  Unknown.  Operculars:  The operculum and suboperculum are about equal and  triangular in Luganoia, while the suboperculum i s smaller and rectangular in Besania. Taxonomy,:  Interoperculum absent. Lehman (1958) raised Brough's family to ordinal status.  Relationships:  Brough states that a l l the characters are holostean  except a) the absence of an interoperculum and the g i l l cover of almost equal operculum and suboperculum, b) the plate-like preoperculum. are amongst the most developed of the subholosteans. characters are:  They  Subholostean  the rounded, hemiheterocercal t a i l and the well spaced  rays of dorsal and anal which equal in number the endoskeletal  supports.  The deep body scales resemble those of the Peltopleuridae and Cephaloxenidae.  / ORDER PELTOPLEURIFORMES Branchiostegals 6-7 elongate spathiform; gulars unknown; operculum and suboperculum present; interoperculum absent. single family.  Upper Triassic. A  97  / Peltopleuridae Pl. Branchiostegals:  Ill  In Peltopleurus about 6-7 elongate 3pathii.'orm  branchiostegals, the uppermost of which is not enlarged. Gulars: Unknown. Operculars:  A large triangular operculum aid a smaller rectangular  suboperculum. Taxonomy:  Lehman (1958) raised Brough'3 family to ordinal status.  Relationships:  From the branchiostegals i t can be said that i t is  unlikely that the Peltopleuriformes arose from the Ptycholepiformes, Redfieldiiformes, Bobasatraniiformes, Haplolepiformes or Dorypteriformes; origin is possible from the Palaeonisciformes, Perleidiformes, or Pholidopleuriformes.  According to Lehman (1958) the scales of Peltopleurus  recall a l i t t l e those of Australosomus; however to the present author the scales seem more similar to those of Cephaloxenus or even Luganoia. Lehman then states that the bones of the cranial roof, with the square parietals and the externally homocercal t a i l recall those of the Perleidae. Altogether, a perleidiform ancestory of the Peltopleuriformes on a common line with the Cephaloxeniformes seems not improbable. References:  Brough (1939), Lehman (1958).  ye ^ ORDER PLATYSIAGIFORMES Branchiostegals about 13, spathiform; gulars unknown; operculum and suboperculum present; interoperculum absent. Lower Jurassic.  Upper Triassic and  A single family. ^ Platysiagidae P I . rv  Branchiostegals:  Number about 13 in Platysiagum minus (text, not  figure of Brough).  These are broad, short and spathiform.  branchiostegal is subrectangular.  The f i r s t  There is a gap, probably a result of  preservation, between this branchiostegal and the others. Gulars:  Unknown.  Operculars: The large operculum sends a wedge-shaped projection into the about equal-sized suboperculum.  A small, concavity on the anterior  half of the lower edge of the suboperculum provides for the presences of a small branchiostegal (called by Brough a modified branchiostegal or incipient interoperculum).  It has been shown that this i s an ordinary  branchiostegal• Hyoid arch: Taxonomy:  Unknown. Brough erected this family and Lehman raised i t to ordinal  status. Relationships:  The presence of about 13 branchiostegals suggests origin  from the Pholidopleuriformes or Palaeonisciformes. References:  Brough (1939), Lehman (1958).  99 t ORDER CHONDROSTEIFORMES Branchiostegals about 9-12,  spathiform; gulars absent; operculum  and suboperculum present; interoperculum absent.  Lower Jurassic. Two  families. ^ Chondrosteidae P l . IV Branchiostegals;  9-10 in Chondrosteus acipenseroides,  about 12 in C.  lindenburgi; the uppermost i s slightly enlarged and the upper 6 and suboperculum are serrate basally on the ventral edge. Gulars:  Gulars absent.  A pair of small curved plates above the anterior  end of the ceratohyal, are believed to be lateral gulars by Watson (1925), but appear to the author more l i k e l y to be hypohyals. Operculars:  Operculum considerably smaller than the subopercular and  shaped like an inverted comma.  Suboperculum large and subquadrate and  serrate on the anterior ventral corner. Hyoid arch: hypohyal.  The "anterior branchiostegal" of Watson appears to be a An ordinary medium sized hourglass ceratohyal i s present.  The remains of an interhyal is suggested in some figures (Woodward, Watson).  It was perhaps unossified.  Relationships:  Discussions under the Acipenseriformes show that  Chondrosteidae cannot be closely related or immediately ancestral to the Acipenseriformes. From the point of view of the number and form of the branchiostegals the Chondrosteidae could have developed from the Palaeonisciformes,  the  100 Perleidiformes, the Ptycholepiformes, or the Platysiagiformes.  But  the dorsal and anal fin rays equal the basals in the Perleidiformes, Platysiagiformes and Ptycholepiformes and the caudal is symmetrical or nearly symmetrical in Pholidopleuriformes.  The latter groups are thus  excluded from the ancestry of Chondrosteidae, leaving the Palaeonisciformes.  Because of the number of branchiostegals, origin is most  l i k e l y from the suborder Palaeoniscoidei.  This conclusion i s in  agreement with Watson (1925) who states . . . "it shows in i t s skull structure clear evidence of Palaeoniscid origin." Lehman (1958) isolates the Chondrosteidae in their own order. This separation may be justified by the lack of a preoperculum in the Chondrosteidae. References:  Woodward (1895), Hennig (1925), Watson (1925). ^ Errolichthyidae  Branchiostegals:  Four elongate spathiform branchiostegals are known.  There may have been more.  The distal half of the branchiostegals  is  divided by three or four grooves - a character unique in teleostomes. Gulars:  Not known*  Operculars:  A large operculum and suboperculum are known.  These bear  grooves on their posterior half similar to those on the branchiostegals. Interoperculum absent. Hyoid arch: Unknown  101  Relationships: uncertain.  The exact phylogenetic position of this family is  The absence of an interoperculum indicates i t s placement in  the chondrostean fishes (Group I).  The discussion under Acipenserif orme3  demonstrates that i t i 3 not closely related or ancestral to that group. Lehman (1952) is followed in placing the Errolichthyidae in the Chondrosteiformes.  ^ ORDER SAURICHTHYIFORMES Branchiostegals about 1 - 3 ; gulars absent; large semicircular operculum; suboperculum and interoperculum absent. Lower Jurassic.  Lower Triassic to  A single family. / Saurichthyidae P l . IV  Branchiostegals;  One long slender lanceolate branchiostegal in  Saurichthys ornatus.  About three long wide branchiostegals  questionably  figured for JS. madagascarensis; in this species they are indicated as being at an angle of about 45° to the mandible, unlike S. ornatus where the single branchiostegal is parallel to the mandible. Gular;  Absent.  Operculars:  Operculum large and semicircular in Saurichthys, smaller in  the Lower Jurassic species.  Suboperculum absent (or may be incorporated  into the operculum). Hyoid arch:  A short curved hypohyal and a very long slender ceratohyal  with the middle slightly constricted, are known to be present.  102 Relationships: uncertain.  The branchiostegal form i n S. madagascarensis i s  That of S. ornatus i s unlike that of any other chondrostean  in i t s extremely elongate form. From the number of branchiostegals i t i s unlikely that the Saurichthyiforme3 are related to the Dorypteriformes, Bobasatraniiformes, Redfieldiiformes or Haplolepiformes.  Stensio (1925)  indicated that many osteological characters and sensory canal characteristics indicate a close relationship to the Acipenseriformes and concludes they are intermediate between the Palaeonisciformes and the Acipenseriformes.  However, the Saurichthyiformes, lacking a  suboperculum, cannot have given rise to Acipenseriformes which possesses one.  Further the supraorbital canal of Saurichthyiformes ends on the  frontal while in Acipenser i t joins the infraorbital canal. Thus the Saurichthyiformes cannot be immediately ancestral to the Acipenseriformes and the long rostra may be a parallelism. References:  Stensio (1925), (1932), Lehman (1952), (1958), Berg (1947),  Griffith (1962). ORDER ACIPENSERIFORMES One branchiostegal; operculum deeply engraved or incised; suboperculum present or absent; interoperculum absent; gulars absent; interhyal, ceratohyal and a hypohyal present. present.  Upper Cretaceous to  Two families.  Several authors, Traquair (1887), Watson (1925), Aldinger (1937), Stensio (1932) and Lehman (1952), (1958) have forwarded views that Chondrosteidae are intermediate between the palaeoniscoids and sturgeons or that they were ancestral to sturgeons.  Wilimovsky (1956) on the other  103  hand expressed doubt that the unarmoured Chondrosteidae were ancestral to the armoured Acipenseridae.  There are further difficulties to  supposing that Chondrosteidae were ancestral, since they lack a suboperculum, clavicle, preoperculum and ribs, a l l of which are found in Acipenseridae.  The caudal i s symmetrical in Chondrosteidae, heterocercal  in Acipenseriformes.  The supraorbital canal according to Traquair's  figures of Chondrosteidae ends on the parietal while in the Acipenserif ormes i t joins the infraorbital canal (liacAlpin, 1947).  Thus  i t seems doubtful that the Chondrosteidae were ancestral to the Acipenseriformes (although i t is possible, though not l i k e l y , that they had a common ancestor not in the distant past). Lehman  (1952) described  a new f o s s i l fish, Errolichthys which he  placed in a separate family in association with Chondrosteidae and Acipenseridae, while  (1958) he  stated that i t was a representative of  an order having characters in common with the Chondrosteidae and Palaeoniscidae.  However, like Chondrosteidae the supraorbital canal  f a i l s to join the infraorbital canal and so cannot be close to the Ac ipen seriforme s. The only chondrosteans in which the infraorbital and supraorbital canals unite are the Redfieldiiformes.  The large eyes, short snout,  terminal mouth, developed teeth of the Redfieldiiformes differ from Acipenseriformes.  The Phanerorhynchiformes considerably resemble the  Acipenseriformes in their long snout, mouth and rows of scutes but are too specialized in their fins to have been ancestral.  However, i t i s  possible that a less specialized ancestor of either of these two orders gave rise to the Acipenseriformes.  104 Finally the presence of an operculum, suboperculum, interhyal and hypohyal argue strongly against Severtzoff*s association of the Acipenseriformes with the Selachii.  These bones are not known in the  Selachii (although Pleurocanthus has a hypohyal), but are found in the Teleostomi.  As ably pointed out in Stensio's (1932) critique of  Severtzoff, the "selachian" characters of Acipenseriformes such as the heterocercal t a i l and spiracle are primitive characters also shared by generalized Actinopterygii. Acipenseridae P l . IV Branchiostegals; are absent.  Most previous authors have stated that branchiostegals  However, examination of a specimen of Acipenser fulvescens  shows a chevron-shaped bene exposed below the operculum. but definitely a branchiostegal.  It i s stubby  Dissection reveals a plate of slightly  larger extent which sends a slight dorsal flange up under the suboperculum, which i s completely skin-covered in this species.  Holmgren and Stensio  (1936) describe and figure the branchiostegal and suboperculum as being at least partly exposed in Acipenser sturio.  The chevron-shaped  branchiostegal of Acipenser i s quite reminiscent of the forked branchiostegal found in Polyodontidae.  The branchiostegal appears to  seat on the interhyal. Gulars:  Absent.  Opercularst  A large grooved circular operculum with an anterior  projection, partly skin covered, i s found. narrow, cartilage, the suboperculum.  Below this i s a small,  Its dorsal end underlies the  105 operculum.  There h a s been debate as to whether the large upper bone  was an operculum or suboperculum.  But the discovery by Holmgren and  Stensio (1936). of a lower g i l l cover bone, the suboperculum, clearly identifies the large upper element i n Acipenser as an operculum.  Gill  membranea joined to isthmus. Hyoid arch:  The hyoid arch is unossified.  ceratohyal, round in cross-section, Relationships: discussed.  A short hypohyal, a short  and cylindrical interhyal are found.  The extra-ordinal relationships have already been  Although the families Acipenseridae and Polyodontidae are  quite ancient, both reaching back to the Upper Cretaceous, the branchiostegal apparatus shows considerable similarity.  The deeply  grooved operculum of Acipenser i s reminiscent of the incised operculum of Polyodon which has degenerated further.  The single chevron-Bhaped  branchiostegal of Acipenser i s not unlike the lone forked branchiostegal of Polyodon.  The hyoid arches of both contain the same elements and are  more or less unossified. small suboperculum.  Acipenser does differ i n the possession of  The ceratohyal of Polydon i s longer, a point  doubtless related to i t s longer mandible.  Despite the similarities  there are many profound differences—scales, rostrum eto. which are found in the oldest fossil forms known and subordinal status may be warranted. Material examined:  Acipenser fulvescens, NMC alizarin specimen, Ontario.  106 Polyodontidae PI. IV Branchiostegals;  In Polyodon a single stout branchiostegal which  divides distally, after a slight upward bend, into four prongs. MacAlpin (1947) reports three or four branchiostegals in the fossil Palaeosephurus.  From his photographic plate of the specimen and his  drawing, i t would appear that he may have mistaken the distal divisions of the branchiostegal as separate branchiostegals.  It i s therefore  suggested that Palaeosephurus possessed only a single branchiostegal. Gulars;  Absent.  Operculars:  A much incised large cartilaginous operculum i s known in  Polyodon and Palaeosephurus.  A suboperculum is absent but by comparison  with Acipenser the g i l l cover bone can safely be identified as an operculum. Hyoid arch:  A short hypohyal, a long ceratohyal and a large quadrate  interhyal comprise the hyoid arch.  The centre portion of the ceratohyoid  i s ossified. Relationships:  Discussion of relationships i s found under Acipenseridae  and the order. References:  MacAlpin (1947), Berg (1947), Gregory (1933), Lehman (1952),  Holmgren and Stensio (1932), Holly (1936). Material examined:  Polyodon spathula, UMMZ alcoholic specimen, U. S. A.  106 a GROUP II.  HOLOSTEI  With interoperculum (or secondarily l o s t ) . One or two hypohyals (or secondarily l o s t ) .  Lateral gulars absent.  Lower Triassic to present.  ^ ORDER OSPIIFORMES Branchiostegals 9-12, spathiform; one or two median gulars present, primitively with  V-3haped  pit line; operculum and suboperculum of about  equal size and interoperculum present.  Lower to Upper Triassic. A  single family. ^ Ospiidae (Parasemionotidae, Tungusichthyidae) P l . IV Branchiostegals:  Number 9-12.  Watsonulus 11 with lower short, upper 3  elongate; Parasemionotus 12 short and broad; Stensioenotus ca. 11; Ospia ca. 11; Jacobulus 11; Tungusichthys 9; Promecosomina 10. Branchiostegals with straight or curved edges and spathiform.  About 8  of the 10 branchiostegals insert on the ceratohyal, the other 2 presumably on the epihyal. Gulars:  Watsonulus has an 8-shaped median gular.  In Parasemionotus the  gular appears to have separated into two portions, a small triangular anterior one and an elongate posterior one slightly notched for reception of the anterior element.  The posterior element bears a V-shaped pit  line anteriorly; there are irregular traces of this pit line on the gular of Watsonulus.  The gular of Jacobulus also bears a V-shaped pit  l i n e , as does the large gular (4/5 of the mandible length) of Promescosomina.  107 Operculars:  Operculum and suboperculum about equal-sized.  operculum appears for the f i r s t time in the Ospiidae.  The inter-  The interoperculum  i s well illustrated in Lehman's fine (1952) photographs of specimens (pis. 39, 4 0 ) • Here the shape of the interoperculum i s identical to that of the adjacent branchiostegal, both having a downcurving expanded anterior end.  The interoperculum differs only in that i t is shorter,  in that i t s posterior end is in contact with the front half of the suboperculum, and in that i t separates the suboperculum from the jaws. The surface pattern of the interoperculum lacks the concentric pattern of the suboperculum.  The form, position and decoration a l l militate in  favor of development of the interoperculum from the uppermost branchiostegal, rather then from fragmentation of an arm of the suboperculum. In Parasemionotus the interoperculum has assumed a more advanced form, being triangular and being more broadly in contact with the suboperculum, thus resembling the interoperculum of the Amiiformes.  But i t s position  and form s t i l l suggest a branchiostegal origin (pi. 42, Lehman, 1952). Hyoid arch:  In Broughia the elongate ceratohyal expands posteriorly  without the usual constriction in the middle; i t i s connected via the "stylohyal" (  a  interhyal) directly to the hyomandibular.  the ceratohyal i s much shortened.  In Parasemionotous  In Promecosomina i t i s heavy, non-  constricted and trapezoidal; i t i s in contact with a triangular epihyal. Taxonomy:  Lehman (1952) unites the Ospiidae and Parasemionotidae, an  action which the author agrees with.  Romer (1955) i s followed in  including the Tungusichthyidae in the Parasemionotidae. priority.  Ospiidae has  108 Promecosomina was raised to family level out of the Semionotidae by Wade. Westoll (1944) doubtfully placed i t in his order Amioidae with the Eugnathidae, Amiidae and Macrosemiidae. believes i t deserves a separate family.  Gardiner (i960)  Lehman (1952) however, believes  that i t s characters conform to those of the Parasemionotidae (=0spiidae). The author concurs with the latter view; the large gular, the 10-12 branchiostegals, and V-shaped gular pit line of Promecosomina agree closely with the Ospiidae.  Although a very large gular plate i s also  found in the Eugnathidae, they apparently lack the V-shaped pit line on the gular.  But i t i s also possible that i t could be associated with  the Catervariolidae of the Amiiformes which have such a V-shaped pit line or with the Semionotidae which also have a V-shaped pit l i n e .  It  i s d i f f i c u l t to t e l l with which family i t should be associated as the specimen of Promecosomina i s incomplete, but the number of branchiostegals would suggest placement with Ospiidae (9-12) rather than Semionotidae (4-6) or Catervariolidae (6). Relationships;  The V-shaped pit lino and f a i r l y numerous branchiostegals  (7-12) of the Ospiiformes recall those of the Perleidiformes.  The  relations of the f i n rays to radials, reduction or absence of the clavicle, scales of lepisosteid type but with vestiges of cosmine layer, a single row of ossified dorsal radials, caudal abbreviate-heterocercal, hyomandibular with opercular process and foramen for truncus hyoideomandibularis n. f a c i a l i s , sensory canals basically paleoniscid, a l l common to both groups also suggest that the-Ospiiformes are derived from the Perleidiformes.  Stensio has proposed that this group evolved from  109  Perleidae or perleid-like Chondrostei.  The Parasemionotiformes probably  gave rise to the Amiiformes. References:  Lehman (1952), Stensio (1932), Berg (1955), Wade (1935). ORDER AMIIFORMES (SEMIONOTIFORMES)  Branchiostegals 5 or 6 - 3 0 ; median gular present, with or without V-shaped pit line; lateral gulars absent; operculum, suboperculum and interoperculum present.  Lower Triassic to present.  Ten families, one  living. The number of branchiostegals, shape of opercular bones and large gular are characters indicating that the Amiiformes were derived from the Ospiiformes or had a common ancestor with them.  In the lower  Amiiformes (Furidae, Semionotidae, Catervariolidae, Signeuxellidae) the supraorbital canal ends on the parietal as i n the Parasemionotiformes. Both Semionotidae and Catervariolidae possess a V-shaped pit line on the gular, as the Ospiiformes.  In both groups there i s a supramaxillary  and the lower jaw i s complex; the fins are holostean; postrostrals are absent; the nasals meet on the midline.  But in the Ospiiformes a  clavicle i s lacking and the preoperculum i s platelike.  It would seem  most l i k e l y that the Ospiiformes and Amiiformes descended from a common ancestor.  Brough (1939) and Gardiner (I960) are also of this opinion. / Furidae (Caturidae, Eugnathidae) PI. V  Branchiostegals:  6 - 2 4 . Furp (=Eugnathus) with 6-12; Euognathus 8 or  10; Hacrepistius about 10; Isopholis 12; Megalurus about 14; Lophiostomus 13; Brachichthys (=Heterolepidotus)  1 6 ;  Caturus  16-30.  In Lophiostomus  110  about 13 with 3 epihyal and 10 ceratohyal; in Caturus 25 with about 4 epihyal and 21 ceratohyal. o  f  The upper branchiostegal (branchioperculum)  Brachichthys and Caturus i s expanded.  Branchiostegals spathiform,  elongate and with curved tips. Gulars:  A large median gular present, apparently lacking a v-shaped  pit l i n e .  In Furq i t almost covers the space between the mandibular  rami, in Caturus i t is about 1/3 to 5/8 the length of the mandible, in Isophili3 i t i s about J the length of the mandible, in Euognathides i t i s diamond-shaped, 1/3 of the length of the mandible and without a pit line.  Said to be small in Brachichthys.  mandible, in Lophiostomus.  Large, about 4/5 of the  Lateral gulars undescribed and presumably  absent. Operculars:  Operculum tending to be larger than suboperculum, the border  between them straight or curved, not wedge-shaped, Heterolepidotus).  (except in  Interoperculum present and triangular.  The figure of  Heterolepidotus (Stensio, 1947) appears to show two interopercula. Hyoid arch:  A small hypohyal, large, deep ceratohyal and a triangular  epihyal known in Furo.  In Lophiostomus the ceratohyal i s angled and at  the anterior end i s expanded. Relationships: large.  The range of branchiostegals in this family i s quite  Brachichthys and Caturus with 16-30 have more than the other  genera known which have 14 or less.  These two genera provide one of the  few examples in which the number of branchiostegals have apparently increased.  Rayner believed that the Furidae were the most primitive of  Ill  the holosteans. References:  Arambourg and Bertin (1958), Berg (1955), Brough (1939),  Eastman (1914), Gregory (1923), Lehman (1949), Rayner (1941), Romer (1955), Schaeffer (I960), White and Moy-Thomas (1940), Woodward (1895), Woodward (1902-12), Z i t t e l (1887). / Acentrophoridae Branchiostegals: Acen^ronhorus,. Gulars:  9-10 curved, elongate, spathiform branchiostegals in The branchiostegals a l l insert on the ceratohyal.  Gulars have not been reported in this group though the bone "x"  in f i g . 13 of G i l l may represent one. Operculars:  Operculum and suboperculum of about equal size; operculum  not sending wedge-shaped projection into suboperculum.  Interoperculum  small, triangular. Hyoid arch: are known. fig.  A hypohyal and a large, elongate, hourglass-shaped ceratohyal The triangular posterior tip of the ceratohyal in G i l l ' s  7 may represent an epihyal.  Relationships:  G i l l states that correspondence of fins and supports,  preoperculum, opercular apparatus and absence of an infra-clavicle place this genus in the Semionotidae (this was before Berg's erection of the Acentrophoridae).  The branchiostegal series do not disagree with  such an alignment but indicate that the Acentrophoridae are more primitive than the Semionotidae. References:  Berg (1947), G i l l (1923)  112  ^ Paracentrophoridae Branchiostegals; Gulars:  10 spathiform branchiostegals in Paracentrophorus.  Not reported.  Operculars:  Operculum and suboperculum of equal size, the former  sending a wedge-shaped projection to the latter.  Interoperculum small  and triangular. Relationships:  According to Piveteau (1941 in Gardiner, I 9 6 0 ) belongs  in Semionotidae, but according to Gardiner deserves i t s own family. References:  Gardiner ( i 9 6 0 ) . /  Branchiostegals:  Semionotidae  In Lepidotea (Lepidotus) about 6 , the uppermost very  broad; in Dapedius 6 broad; in Semionotus at least 4 to 1 4 .  A figure of  Lepidotes montelli shows at least 6 slender branchiostegals attached to the epihyal. Gulars:  Missing in Lepidotes.  Dapedius with a large median gular plate  half the length of the mandible and bearing a V-shaped pit l i n e . Operculars:  The operculum larger than the suboperculum and extending  into the suboperculum in a curve or a wedge.  Interoperculum a primitive  triangle, (Lepidotus) or a rectangle (Dapedius). Hyoid arch:  A triangular hypohyal, an hourglass-shaped ceratohyal and an  epihyal in Lepidotes.  In Dapedius epihyal much contracted at proximal  end and ceratohyal remarkably short and deep (in association with i t s  113  short jaws). Taxonomy: Berg  (1947) states  the Semionotidae are doubtless a  heterogeneous assemblage and separates them from the Acentrophoridae. Romer places Acentrophoridae i n Semionotidae. Relationships:  The close similarity of fins, form and skull bones leave  l i t t l e doubt of the very close affinity of Acentrophorus to Lepidotes. But Berg gives presumably adequate characters to separate them as families:  frontals fused or paired; caudal heterocercal or abbreviate  heterocercal; pectorals high or low.  To these differences may be added  the connection of the supraorbital canal with the temporal canal and the form of operculum (in Acentrophorus operculum equal to suboperculum and not sending a wedge into i t ; in Lepidotus operculum larger than suboperculum and sending a wedge into i t ) .  Geologically Acentrophorus  i s older (Upper Permian) than Semionotidae (Lower Triassic to Lower Cretaceous). Gardiner (i960) derives Semionotus and Acentrophorus separately from the palaeoniscid fishes, not from the amiiform line. This derivation seems unlikely as i t would c a l l for a second parallel development of the interoperculum. References: Woodward (1895), Romer (1955), Gardiner (I960), Eastman (1914).  Ilk ^ Catervariolidae Branchiostegals:  6 small, elongate, spathiform branchiostegals in  Catervariolus hornemani.  The uppermost i s covered basally by the  interoperculum. Gulars:  A large median gular occupies at least half the length of the  mandible.  A V-shaped pit l i n e , apex posteriormost, is found on the  anterior end.  A pair of wide lateral gulars, with width occupying about  1/3-1' of the mandible, may be present.  Saint-Seine states they are  probably present and dots i n their outline in his figures.  If so„, they  are the only family of Amiiformes or Group II known to possess lateral gulars. Operculars:  Interoperculum denticulate.  Hyoid arch:  A ceratohyal and a large short wide ephihyal are known.  Taxonomy:  This family was recently created by Saint-Seine.  Relationships: Amiidae.  Saint-Seine placed this family in association with the  The V-shaped pit l i n e , number of branchiostegals, supraorbital  pit line ending on the parietal a l l indicate relationship with the Semionotidae, rather than the Amiidae. References:  Saint-Seine (1955), Arambourg and Bertin (1958). / '  Branchiostegals:  Signeuxellidae  A single elongate curved spathiform branchiostegal is  seen in an incompletely preserved specimen; probably there were several.  115  Gulars: Unknown. Operculars: operculum.  A large operculum sends a wedge into the smaller subBelow is a f a i r l y large triangular primitive interoperculum.  Hyoid arch: Taxonomy:  Unknown. Saint-Seine erected this family in 1 9 5 5 .  Relationships:  Other than placing the Signeuxellidae in the holostean  stage Saint-Seine was uncertain of the affinities.  Dorsal views of the  opercular bones i n Signeuxella look very similar to those in Catervariolus. The supraorbital line ceases on the parietal in both genera.  These and  other characters suggest they may be related. References:  Saint-Seine  (1955),  Arambourg and Bertin  (1958).  J Macrosemiidae Branchiostegals:  5 - 6 , perhaps to 9 in Macrosemius rostratus; these  shaped l i k e a scimitar and inserting on the ceratohyal.  Four spathiform  branchiostegals with rounded tips known in M. helenae, the upper inserting on the epihyal, the others oh the ceratohyal.  About 1 0 in  Ophiopsis, at least 7 in Propterus. Gulars:  A gular plate has been observed only in Ophiopsis and Eusemlus.  Operculars: down into i t . Hyoid arch:  Operculum larger than the suboperculum and sending a wedge Interoperculum f a i r l y large, and triangular. Epihyal, ceratohyal and hypohyal present.  116 Relationships:  The Macrosemiidae were doubtless derived from a  semionotid such as Lepidotus, as was discussed under that family, although Rayner and Bertin and Arambourg suggest derivation from Eugnathidae (=Furidae).  Although the infraorbital and supraorbital  canals join in Sinamiidae, Lombardinidae and Amiidae, as well as in Macrosemiidae, Macrosemiidae does not seem closely related to any of these families.  Macrosemiidae retains the branch of the supraorbital  canal which terminates on the parietal, unlike the other families, a character which would seem to be primitive.  The scales are rhomboid  and thus more primitive than those in Amia.  But on the other hand i t  has fewer branchiostegal rays than Amia, References:  Woodward (1895), Arambourg and Bertin (1958), Z i t t e l (1887),  Rayner (1941), Eastman (1914). ^ Sinamiidae Branchiostegals:  Branchiostegals questionably suggested by dotted lines  to number about 14 in restoration figure of Berg (after Stensio). Gulars:  Unknown.  Operculars:  Operculum larger than suboperculum and sending a slight  wedge into i t .  Interoperculum a long triangle.  The opercular bones  much resemble those in Amia. Hyoid arch: Unknown. Taxonomy:  Although Romer (1955) and Arambourg and Bertin (1958) place  Sinamia in Amiidae, Sinamia i s here retained in i t s ow\ family for the  117 reasons given by Berg. Relationships:  The close similarities of Sinamia and Amia leave l i t t l e  doubt that they are related.  However, the fused condition of the  parietals in Sinamia indicate that Sinamia was not directly ancestral to Amia.  Their similarities must thus arise from having a close common  ancestor. References:  Berg  (1947). ^ Lombardinidae  Branchiostegals:  Unknown.  Gulars: Unknown. Operculars:  Large vertical rectangular operculum, small, elongate,  horizontal suboperculum, small primitive interoperculum. Ryold arch: Unknown. Taxonomy:  This family was recently erected by Saint-Seine  Relationships:  (1955).  Although the form of the opercular bones does not differ  greatly from Catervariolidae and Signeuxellidae, the figure seems to indicate juncture of the infraorbital and supraorbital sensory canals, as in the more advanced Amiiformes.  The t a i l i s almost heterocercal,  the scales rhomboid. Lack of data on the branchiostegals enables l i t t l e further statement to be made. References:  Saint-Seine  (1955),  Arambourg and Bertin  (1958).  118 Amiidae PI. V Branchiostegals;  In Amia 10-13; in /Megalurus 11-12.  spathiform with curved tips. ceratohyal.  Form elongate and  The branchiostegals a l l insert on" the  The uppermost branchiostegal i s dilated and has been termed  the branchiosperculum by Hubbs. Gular;  A large median gular i s present i n Amia.  2/3 that of the mandibles. Operculars:  It is bereft of a p i t l i n e .  Operculum larger than the suboperculum and sending a wedge  down into i t . Hyoid arch;  Its length i s about  Interoperculum small, elongate, and triangular. A triangular hypohyal, angulate large ceratohyal, triangular  epihyal with a prong inserting on outer ceratohyal and small cylindrical unossified interhyal. Relationships:  As stated under Sinamiidae, the Amiidae probably share a  close common ancestor with that family.  The ancestral form was probably  near to the Furidae, judging by the branchiostegals and median gular plate. References:  Berg (1947)* Jordan and Everman (1896), Hubbs (1920),  Agassiz (1833-43). Material examined:  Amia calva, 11 alizarin specimens, MMC58-192-S, Pt.  Pelee, Ontario; 12 alizarin specimens, NMC58-209, Georgian Bay, Ontario; alcoholic specimen, BC59-426,  Illinois.  119 ORDER LEPISOSTEIPORMES (LEPIDOSTEIFORMES) Branchiostegals 3, spathiform; gular3 absent; operculum and suboperculum present; interoperculum absent*  Upper Cretaceous to present.  A single family. Lepisosteidae Pl. V Branchiostegals;  3 small spathiform branchiostegals.  The upper two  are attached to the epihyal, the other to the ceratohyal.  The uppermost  i s broad, the lower two attenuate. Gulars:  Absent.  Taxonomy: The generic name was originally spelled Lepisosteus by Lacepede. This spelling has been incorrectly emended to Lepidosteus by some authors.  Arambourg and Bertin (1958) include the Lepisosteidae in  the same order as Amia. The many skeletal oddities of Lepisosteidae would, in the authors opinion, justify i t s ordinal separation. Relationships:  The modifications of the skull of Lepisosteiformes make  i t s placement d i f f i c u l t .  Most authors include i t in Holostei. The non-  platelike form of the preoperculum, rudimentary clavicle, absence of cosmine layer in the scales, maxillary not immovably connected with the preoperculum and dorsal and anal pterygiophores each supporting a single ray, and t a i l not heterocercal, are characters indicating holostean placement.  However, the f i n rays are completely segmented and some of  the above holostean characters jnight be modifications resulting from the peculiar jaws.  S o the question of placement i s not entirely settled.  120 Rayner (1943), from neurocranial study, believes the Lepisosteidae are derivable from the Semionotidae.  Gardiner (i960) also considers such  an origin l i k e l y . References:  Berg (1947), Arambourg and Bertin (1958), Boulenger (1904),  Regan (1923), de Beer (1937). Material examined:  Lepisosteus osseus, alizarin specimen, NMC6O-478-A,  Ontario; skeletal specimen, USNM 110191, U. S. A. Operculars:  An operculum and suboperculum of approximately equal size  are present, the f i r s t sends a wedge into the latter. The absence of an interoperculum i n this presumably holostean fish has caused a number of authors to identify other elements as the interoperculum.  The preoperculum has been identified as an interoperculum by  Regan (1923).  The passage of the preoperculo-mandibular canal through  this bone clearly identifies i t as the preoperculum however,  Holmgren  and Stensio (1936) c a l l the small bone above the anterior end of the preoperculum, the interoperculum.  However, that this bone develops in  this position, l i e s above the preoperculo-mandibular canal and i s far from the epihyal and suboperculum which true interopercula contact.  It  i s therefore probably the quadrato-jugal as suggested by Hammarberg (in Arambourg and Bertin, 1958).  The upper branchiostegal has also been  identified as the interoperculum (de Beer, 1937).  But this element does  not l i e i n the same horizontal fold as the suboperculum, does not l i e over the outer face of the epihyal, and does not insert on the suboperculum or jaw, a l l relationships which make i t d i f f i c u l t to identify as an  121 interoperculum.  The interoperculum must therefore be considered to  have been lost (or was never present in which case Lepidosteiformes should be placed in the Chondrostei).  The very anterior jaws and the  downward expansion of the preoperculum into the normal position of the interoperculum are both changes which could have lead to the loss of the interoperculum. Hyoid arch:  Consists of a hypohyal, a short ceratohyal round in cross  section, and a short epihyal with a small backward projection on which sits the upper branchiostegal.  A small cartilage on top of the epihyal  may represent the interhyal. / ORDER ASP IDORHYNCHIFORMES Branchiostegals 12-13 spathiform; gulars absent; large operculum and small suboperculum present; advanced interoperculum present. Jurassic to Upper Cretaceous.  Middle  A single family.  / ORDER ASPIDORHYNCHIFORMES Branchiostegals 12-13 spathiform; gulars absent; large operculum and small suboperculum present; advanced interoperculum present. Jurassic to Upper Cretaceous.  Middle  A single family.  / Aspidorhynchidae Pl. V Branchiostegals:  12-13 elongate spathiform branchiostegals in  Aspidorhychus acutirostris; several large branchiostegals in Belonostomus. Gulars:  Apparently absent  122  Operculars:  In Aspldorhynchus operculum large, suboperculum small;  together forming a hemicircle.  Interoperculum completely under the  preoperculum; without dorsal projection posteriorly; subrectangular. Hyoid arch:  Ceratohyal very large, epihyal small.  Relationships:  The branchiostegals and opercular bones are most similar  to those of the Amiiformes, particularly those of the Amiidae. There are two large postorbital bones, fulcra are lacking, and the lower jaw complex is as in Amia. i s as in adult .Amia.  Berg states the sensory canal system on the head Differences in the scales, dorsal fins, rostrums  indicate that Amia cannot be directly ancestral to Aspidorhynchus which therefore must have descended from a common ancestor.  In this regard  Berg points out the parietals are fused in Aspidorhynchus, as in Sinamia and i t may be noted that the opercular bones of Aspidorhynchus are more similar to those in Sinamia.  Further, the scales of Sinamia are rhombic  and supraorbitals are present as in Aspiorhynchus but unlike Amia.  It  therefore seems that Aspidorhynchus i s more closely related to the sinamiid line than to the amiid l i n e .  The advanced form of the inter-  operculum is probably associated with the L-shape of the preoperculum. Gardiner (I960), however, suggests that the Aspidorhynchiformes maybe derived from the Pholidophoriformes; the branchiostegal series do not argue against this. References:  (1833-43).  Assman (1906; in Berg, 1947); Woodward (1895); Agassiz  123 / ORDER PACHYCORI^IFORMES Branchiostegals (6+-) 30-50* spathiform; median gular present; lateral gulars appear absent; equal sized operculum and suboperculum; triangular f a i r l y advanced interoperculum present. Upper Cretaceous.  Upper Triassic to  A single family.  Taxonomy: Following Romer (1955) and Arambourg and Bertin (1958) Protosphyraenidae i s synonymized with Pachycormidae.  Woodward (1895) said  that Protosphyraenus differed l i t t l e from Hypsocormus (Pachycormidae). However, contrary to Arambourg and Bertin, the Pachycormidae is not placed in the same order as the Amiidae.  In addition to the characters  by which Berg distinguished the Pachycormiformes, there are the greatly enlarged lower postorbital and the numerous branchiostegals. / Pachycormidae Branchiostegals:  In Pachycormus 4°-50 with about 22 on the epihyal and  20 on the ceratohyal.  Figures of Hvpsocormus show a complement, presumably  incomplete, of about 6. Z i t t e l (1887) gives the number for the family as 30-45. Branchiostegals elongate, rectilinear and spathiform. Gulars:  A large median gular about ^ the length of the mandible i s  found i n Pachycormus, a smaller oval one in Hypsocormus. present in Protosphyraena. Operculars:  Lateral gulars have not been reported.  Operculum very large and triangular, suspended vertically  by the apex, larger in Hypsocormus than in Pachycormu3. equally large. Pachycormus.  A gular i s  Suboperculum  Interoperculum small triangular and f a i r l y advanced in An interoperculum is not mentioned in Protosphyraena or  124 Hypsocormus nor i s i t present in figures of the l a t t e r .  Presumably  specimen(s) of Hypsocormus are incomplete, as the interoperculum and some branchiostegals appear to be lacking. Hyoid arch:  Epihyal, a broad more or less straight ceratohyal and a  hypohyal are known in Pachycormus.  A longitudinal groove i s found on  the meeting ends of the ceratohyal and epihyal. Relationships:  It seems l i k e l y that the Pachycormiformes arose from the  Eugnathidae which also had numerous branchiostegals (up to 24). The large postorbitals of the Eugnathidae also suggest this.  Since more  branchiostegals are found in Pachycormiformes this provides a second example of the rare phenomena of the branchiostegal number increasing along a phylogenetic sequence; although i t might be taken as one example, the branchiostegals increasing in the eugnathid-pachycormid l i n e .  In  any case where parts are numerous and unspecialized the ability to increase i s often retained. References:  Woodward (1895, 1898), Z i t t e l (1887), Lehman (1949). / ORDER PHOLIDOPHORIFORMES  Branchiostegals 1 (?) 6-18*; narrow gular plate; operculum larger than suboperculum; interoperculum small; opercular bone borders entire; Middle Triassic to Upper Cretaceous.  SLx families.  125 / Pholidophoridae PI. V Branchiostegals:  7-10 in Pholidophorus, curved and spathiform.  The  upper branchiostegal i s axpanded distally in some species. Woodward (1895) reports at least 17 pairs of branchiostegals in Pholidophorus (?) dubius. Gulars: bechi.  A narrow median gular with a median ridge in Pholidophorus Gulars unknown in other forms.  Operculars:  Large triangular operculum with apex ventral; triangular  suboperculum with apex dorsal, slightly smaller than operculum.  Inter-  operculum primitive and triangular. Relationships:  The Ospiiformes show some resemblances but differ in  the form of the preoperculum and interoperculum.  Gardiner (i960)  believes the Ospiiformes gave rise to the pholidophorids.  A closer  resemblance is seen in the Amiiformes such as Semionotidae and Eugnathidae.  Although the Macrosemiidae also resemble tho Pholidophoridae  they are precluded from ancestry by the fusion of the supra- and infraorbital canals which end on the parietal without fuoing with the infraorbital canal in the family Pholidophoridae, Pleuropholidae and Majokiidae.  The close resemblance of the opercular apparatus, cephalic  sensory canal3, postorbitals, irregular median line of the paired roofing bones of the skull suggest a eugnathid origin as most l i k e l y . References:  Woodward (1895).  126  / Pleuropholidae Branchiostegals:  At least 2 branchiostegals in Parapleuropholis.  These  are spathiform, straight, elongate and broaden distally. Gulars:  Unknown and presumably absent in Pleuropholis.  Operculars: small.  Operculum very large and vertically rectangular; suboperculum  Interoperculum long and advanced, sending a dorsal arm up behind  •the preoperculum and about on level with the suboperculum. Relationships:  The branchiostegals and operculars are slightly different  in form from those in Pholidophoridae.  According to Arambourg and Bertin  Pleuropholidae are very close to Pholidophoridae.  The number of branch-  iostegals i s considerably lower in Pleuropholidae, but i t is not certain that the series i s incomplete. References:  Arambourg and Bertin (1958). ^ Liguellidae  Branchiostegals:  In Liguella there i s at least one elongate, curved,  spathiform branchiostegal which expands distally. Gulars:  Unknown and presumably absent.  Operculars:  Large rectangular operculum; small suboperculum.  Inter-  operculum not preserved, but presumably present. Taxonomy: Family erected by Saint-Seine. Relationships:  From the fragmentary remains preserved l i t t l e can be  127 said.  The branchiostegals are curved, rather than straight as in  Pleuropholidae, but in both they expand distally. References:  Saint-Seine (1955), Arambourg and Bertin (1958). f Majokiidae  Branchiostegals: Gulars:  Mot preserved.  Not known.  Operculars:  Operculum large, quadrate; suboperculsr small, triangular  and denticulate. Taxonomy:  Interoperculum ending posteriorly in a spine.  Family erected by Saint-Seine.  Relationships:  Fragmentary remains enable l i t t l e to be said about this  group. References:  Saint-Seine (1955), Arambourg and Bertin (1958). Oligopleuridae  Branchiostegals:  In Oligopleurus at least 6 elongate, curved, spathiform  branchiostegals distally expanded, in Oeonoscopus about 13. Gulars:  Not observed.  Operculars:  Opercular large, quadrate; suboperculum small.  Lower limb  of preoperculum large and obscuring interoperculum, i f present. Hyoid arch:  Ceratohyal and epihyal present.  128 Relationships:  The branchiostegals would enable this group to be  derived from the Pholidophoridae.  It may be noted that the Archaeomaenidae  and Oligopleuridae have cycloid scales while the Pleuropholidae, Pholidophoridae, Liguellidae, and Majolciidae have rhombic scales. places thi3 family in Pholidophoriformes.  Berg  Miss Rayner believes the  family slightly off the main Pholidophorus-Leptolepis line of evolution. Bertin and Arambourg place the family in the Leptolepiformes because of the fusion of the infra and supraorbital canals, probable loss of rostrals, and reduction of parietals and premaxilleries.  But these two sensory  canals do not join in Leptolepidae. References;  Woodward (1895), Rayner (1948), Bertin and Arambourg (1958),  Berg (1947), Woodward (1890). GROUP III.  TELEOSTEI  With interoperculum (or secondarily l o s t ) .  Lateral gulars absent.  Two hypohyals (or secondarily one or both l o s t ) . MALACOPTERYGII Branchiostegals 0-36, one or more often spathiform. only in primitive clupeiforms. Siluroidei and Beloniformes).  Median gular  Epihyal and ceratohyal separate (except Never spines on opercular bones.  Seldom  with acanthopterygian pattern of 4 external and 0-4 (5-7) ventral or internal. The division of teleost fishes into malacopterygian and acanthopterygian on the basis of branchiostegals ha.s recently received support by a study on  the retractores arcuiim branchialium by Holstvoogd (1963).  Holstvoogd  129 (1963 and in l i t t . ) reports the malacopterygian groups studied, Clupeiformes, Mormyriformes, Cypriniformes, Notacanthiformes, Anguilliformes (and Polypteriformes) lack the muscle retractores arcus branchialium. On the other hand, the acanthopteryian groups studied possess this muscle:  Gadiformes, Gasterosteiformes, Syngnathiformes, Ophidiiformes,  Percopsiformes, Cyprinodontiformes, Mugiliformes, Perciformes, Pleuronectiformes, Gobiesociformes, Tetraodontiformes, Mastastembeliformes and Batrachiiformes.  The Myctophiformes also possess this muscle; as i s  discussed later this order may be close to the lineage that gave rise to the acanthopterygians.  The Beloniformes also possess this muscle;  this is puzzling since they are usually considered malacopterygians. Except for the latter, conclusions from the muscle study and the study of branchiostegals are in complete agreement. ORDER CLUPEIFORMES Branchiostegals 2-36, with 0-1 interhyal, jg-12 epihyal, 0-23 ceratohyal and 0-5 hypohyal, with 2-12 external and 0-11 ventral (or rarely internal).  Median gular present only in Albuloidei and more  primitive suborders.  Operculars complete, without spines and usually  entire (rarely crenualte).  Interhyal, epihyal, ceratohyal and two  hypohyals present (except interhyal and one hypohyal absent in Phractolaemidae).  Lower Cretaceous to present.  Fifteen suborders and  54 families, 15 of which are known only from f o s s i l s . Gosline (i960) divided the Clupeiformes into two divisions, Clupei and Osteoglossi.  The Osteoglossi, with the exception of Iliodontidae,  are here removed to the Mormyriformes, as discussed under that order.  130 The Hiodontidae are placed in a new suborder within the Clupeiformes. Although the Clupeiformes do show some relationship t o t h e Pachycormiforme3, there seems l i t t l e doubt t h a t their closest relationships are to the Pholidophoriformes.  Besides t h e similar branchiostegals,  several other characters are shared:  two supramaxillaries, lower jaw  without prearticular and coronoids, and without independent supraangular. Rayner (1948) considered the two groups very close.  Gardiner (i960) was  of the belief that the teleosts arose from the Pholidophoriformes. Some authors have considered that the Elopoidei may belong in the Holostei (Saint-Seine, 1956, Nybelin, 1957), on the basis of such characters as the ethmoid commisure connecting the infraorbital canals and the possession of a gular. regarded as primitive holdovers.  However, these characters may be The development of a second hypohyal  and of intermuscular bones clearly distinguishes the members of the Clupeiformes from their predecessors.  The only alternate solution would  be placement of the Lycopteroidei, Leptolepoidei and Elopoidei together in their own order.  But this has l i t t l e merit as the Albuloidei s t i l l  retain a vestige of a median gular.  So rather than establish a poorly  defined order on the basis of this receding character i t appears preferable to establish an order on the sharply defined grounds of the two new characters. / SUBORDER LYCOPTEROIDEI / Lycopteridae Branchiostegals:  At least 6 or & to 10 spathiform.  middendorffi 10 with 3 epihyal and 7 ceratohyal.  In Lycoptera  131 Gular:  A median gular present i n Lycoptera, less than one half length  of mandible. Operculars: and with  Operculum large and rectangular above small suboperculum  interoperculum.  References: Woodward (1895), Berg (1948a). / SUBORDER LEPTOLEPOIDEI / Leptolepidae Branchiostegals:  In Leptolepis about 21 with 9 broad and imbricating  on the epihyal and about 12 spaced and delicate ones on the ceratohyal. Gular:  Leptolepis with a median gular one half the length of the  mandible. Operculars:  Complete and entire.  Hyoid arch:  Ceratohyal with ordinary hourglass-shape but noteworthy for  the extension of a supplementary delicate rod of bone between i t s extremities on the upper side and for i t s large central perforation; interhyal, epihyal and one large hypohyal present. References: Woodward (1895), Berg (1947), (1948), Rayner (1937), Nybelin (1963). SUBORDER ELOPOIDEI Branchiostegals at least 16-36 with 5-13 epihyal and 10-23  ceratohyal,  about 12 being slightly external and 20-23 being ventral, the upper ones spathiform the lower ones becoming  3lender.  A well developed but narrow  132 median gular 1/3 to ^ the length of the mandible. Leptolepidae has but one). membrane separate.  Two hypohyals (except  Operculars complete and entire.  Gill  Five families, two l i v i n g .  Jordan, Evermann and Clark (1930) include the elopid families and albulids in separate suborders. Clupeoidei.  Berg (1947) places both in the Suborder  Gosline (i960) places both in the Suborder Elopoidei  (separate from the Clupeoidei) but recognizing two superfamilies, Elopoidae and Albuloidae.  It is the author's opinion that Jordan,  Evermann and Clark were correct in awarding subordinal status to the two groups.  The two groups differ in numerous profound characters.  The  Albuloidei (Albulidae and Pterothrissidae) differ trenchantly from the Elopoidei (Alopidae and Megalopidae) in the following characters:  1-3  branchiostegals instead of 5-13 on the epihyal; gular plate rudimentary or absent versus well developed; one versus two supramaxillaries; pelvic rays 10-14 instead of 15-17; maxillaries toothless instead of toothed; subterminal instead of terminal or superior mouth; g i l l rakers tuberclel i k e instead of long and slender; only tvro pairs of uroneurals instead of 4; terminal vertebra with no neural arch and with a greatly expanded median crest behind i t instead of with a neural arch and a small median crest; 7 hypurals instead of 8-9; one posterminal centrum instead of two (characters from Berg, 1947, Hollister, 1939, Gosline, 1961, Gregory, 1933).  These differences show the albuloids are considerably advanced  with respect to the elopoids. Ridewood (1904) came to a similar opinion after study of their skulls, "There i s no doubt that the ELopidae are the most archaic of existing teleosteans and that the Albulidae are in few respects more highly specialized; but the study of the skull does not  133 show any direct affinity between the two families".  Nybelin (i960)  although he discovered the rudimeritarj'- gular plate in Albula felt that "The detection of this plate naturally does not mean that Albula vulpes would have a closer relationship to the Elopidae and Megalopidae than what has so far been assumed, for i t i s clear from other facts Elops, Megalops and Albula a l l represent evolutionary lineages of their own". The two groups are therefore treated as separate suborders. Elopidae {f Raphiosauridae) Branchiostegals:  Vary from 16 to 36, i n ^Laminospondylus transversus  16 or more; i n ^Rhacolepis about 20; in ^Thrissopater about 30; i n /Esocelops at least 15; in /spaniodon at least 15; in ^Osmeroides 20 with 5 broad ones on the epihyal and 15 on the ceratohyal; in /Pachyrhizodus 9-10 on the epihyal; in Elops 24-36 with 12 epihyal and 20-23 ceratohyal, the upper 12 being slightly on the lateral face, the remainder on the ventral face of the arch; the upper ones being broad and expanded, the lower narrow and elongate. Gular:  In Elops elongate narrow median gular occupying about one third  of the mandibles; no pit line apparent on i t . least  of mandible.  In Esocelops gular at  In Osmeroides long and narrow, i t s length slightly  more than <?- mandible. Operculars:  Complete, operculum large, interoperculum triangular and  modern. Hyoid arch: in Elops.  Consists of 2 hypohyals, ceratohyal, epihyal and interhyal  134  References:  Springer (1957), Woodward  (1901),  (1902-1912), Ridewood  (1904), Fowler (1936), Weber and de Beaufort (1913), Regan (1909).  Material examined;  5  Elops saurus,  BC55-321, Louisiana,  alcoholic;  USNM26218, Key West, skeleton. Megalopidae Branchiostegals:  Megalops  23-27 with  13 epihyal and 10-12 ceratohyal.  The range of counts in the two species atlanticus and cyprinoides are identical. Gular;  A narrow elongate diamond-shaped gular without trace of pit l i n e .  Its length slightly exceeds half the length of the mandible.  Attached  by a ligament to the back of the mandibular symphysis. Operculars;  Complete and entire; a narrow suboperculum forming half the  posterior border of the g i l l cover behind the operculum; suboperculum narrow. Hyoid arch;  An interhyal, epihyal, ceratohyal and two hypohyals present.  Relationships:  The number and arrangement of the branchiostegals on the  hyoid arch is similar to that in Elops.  The gular i s somewhat longer in  Megalops than Elops but other f o s s i l elopids have an equally long i f not longer gular.  The branchiostegal series therefore do not offer support  to retention of the Elopidae and Megalopidae in separate families.  Some  authors do not separate them. References:  Fowler (1936), Day (1&75), Weber and de Beaufort (1913),  135  Ridewood (1904).  1 Megalops atlanticus, U3NM 179715, British Guiana,  Material examined; skeleton.  / Ganolytidae Branchiostegals:  No data available. SUBORDER ALBULOIDEI  Branchiostegals (4) 6-16 with 2-3 epihyal and 10-12 ceratohyal, 11 external and 1 ventral. complete and entire.  A rudimentary gular present or absent.  G i l l membranes separate.  ceratohyal and two hypohyals present.  Operculars  Interhyal, epihyal,  Two families.  Albulidae P l . VI Branchiostegals.  In ^Chanoides probably about 4; in /Ancylostylos  probably 6; Albula 10-16.  Albula vulpes observed (10) 11-13 left and 10-  11 right with 2 epihyal and 10 ceratohyal, 11 external and 1 ventral. While (10) 11-13 branchiostegals were found in 14 specimens from the Pacific coast of America (Peru to Mexico), Day (I875), Misra (1953) and Weber and de Beaufort (1913) report 14-16 from India and the IndoAustralian Archipelago.  This might suggest two species are involved.  In Albula vulpes the upper branchiostegals are broadly spathiform becoming narrower ventrally; they are a l l decurved and have a median external ridge basally.  The lowest ones may not contact the ceratohyal  but may be free in the membrane.  136 Gular;  Nybelin (i960) discovered the presence of a very slender median  gular about ^ the length of the mandible in Albula vulpes. rudimentary compared to that of the elopoids. only a threadlike trace was observed.  It is  In 3 and 6 inch specimens  The gular i s contained in a gular  fold which, curving anteriorly, joins the two mandibles.  Its posterior  border is crenulate. Operculars;  Opercular bones complete and entire, suboperculum V-shaped.  Hyoid arch;  Consists of 2  References:  Misra (1953); Weber and de Beaufort (1913); Ridewood (1904);  h y p o h y a l 3 ,  ceratohyal, epihyal and interhyal.  Woodward (1901). Material examined:  10 specimens of Albula vulpes. BC56-160, from Peru  one of which was cleared and stained for detailed examination; 3 alcoholic specimens, BC59-687, from Panama, Panama; one alcoholic, BC56-162, from Talara, Peru; one alcoholic, BC60-14, Acapulco, Mexico. Pterothrissidae Branchiostegals: Gular:  In ^Istieus about 10; in Pterothrissa gissu 6.  Pterothrissa lacks a median gular plate.  Operculars:  Complete and entire.  Relationships:  Differences in the possession of gular plate, dorsal f i n ,  dentition of the maxillary, etc. would certainly warrant their familial separation, although some authors have considered Pterothrissidae a subfamily of Albulidae.  137 References:  Gunther (1887), Woodward (1901), Tomiyama and Abe (1958),  Material examined:  None. SUBORDER CLUPEIODEI  Branchiostegals 5-20, with 1-5 epihyal and 0 - U ceratohyal, 2-10 external and 0-11 ventral. entire.  Gular absent.  G i l l membranes separate.  Operculars complete and  Interhyal, epihyal, ceratohyal and  two hypohyals in a l l families examined.  Fourteen families, four of  which are known only from f o s s i l s . The branchiostegal rays of Alepocephaloidea tend to be long and slender while at least the upper branchiostegals of Clupeoidea are broad and one or more bears a clupeoid projection.  The branchiostegals of  Rosauridae are suggestive of the Alepocephaloidea. Superfamily Alepocephaloidea Alepocephalidae Branchiostegals:  Vary from 5-9, but 13 in Leptochilichthys, a l l slender  and lath-or rod-shaped.  In Alepocephalus 6, Anamalopterichthys 7,  Asquamiceps 5, Aleposomus 6-7, Bathytroctes 7-8, Bellocia 6, Conocara 6, Ericara 6, Grimatotroctes 7, Leptoderma 7, Leptochilichthys 13, Macromastax 9, Micrognathus 7, Mitchillina 6, Narcetes 8, Nemabathytroctes 7, Photostylus 6, Rouleina 6, Talismania 6-8, Tauredophidium 8, and Xenodermichthys 6-7. Talismania bifurcata 7 with 4 epihyal and 3 ceratohyal, 4 external and 3 ventral, slender, elongate and distally slightly laminar. Operculars:  In Alepocephalus operculum crenulate, suboperculum and  interoperculum entire.  In the family the g i l l membranes separate,  138 sometimes united and free from the isthmus. Hyoid arch;  Consists of interhyal, epihyal, ceratohyal and two hypohyals  in Talismania. Relationships;  Leptochilichthys differs quite strongly from other  alepocephalids in having 13 branchiostegals instead of 5-9. References; Weber and de Beaufort (1913), Grey (1958), Fowler (1936), Parr (1937, 1951, 1952), Maul (1948), Beebe (1933), Garroan (1899), Tucker (1954), Gunther (1887), Misra (1953). Material examined; Bathytroctes rostratus, alcoholic specimen, USNM 137754-9, Philippines; Talismania bifurcata, alcoholic specimen, BC62-159, California. Searsiidae Branchiostegals:  Vary from 4 to 8.  In Persparsia 7, Pellisolus 7,  Holtbyrnia 7-8, Searsia 7-8, Normichthys 8, Mirorictus 4, Platytroctes 5-6, Sagamichthys 6, Maulisia 7-8, Mentodus 7-8, Barb an tus 7-8. Relationships;  Parr (1951) separated this family from  It i s very closely related to the Alepocephalidae, only by the presence of the shoulder organ.  Alepocephalidae.  being distinguished  The similarity of the  branchiostegal counts would confirm the closeness of their relationship.  References; Parr (1951, I960), Maul (1954, 1957), Tucker (1954).  139 Macristiidae Branchiostegals: Operculars:  Long, slender, curved vdth about 8-10 in Macristium.  Complete and entire*  Relationships:  G i l l membranes free.  Regan f i r s t placed this fish i n the family Scopelidae;  later he modified his view making i t a distinct family close to the Alepocephalidae. was uncertain.  Berg followed the latter view but stated i t s position Marshall (1961) on the capture of a second young specimen  suggested that Macristium was the survivor of the f o s s i l ctenothrissid fishes. This author i s inclined to disagree with the latter opinion. While the number of branchiostegals i n the Ctenothrissidae and Macristiidae are about the same, the form of the branchiostegals i s not.  While the  upper two branchiostegals i n Ctenothrissidae are broad and spathiform, in Macristiidae a l l of the branchiostegals on the contrary are narrow. Scales are absent i n Macristiidae, present i n Ctenothrissidae. As Marshall points out the Macristiidae lack supramaxillaries while there are two well developed ones i n the Ctenothrissidae.  The number of  vertebrae differ by about 20. The similarities i n f i n pattern and mouth angle may be a result of similarity i n habits; they are not strong subordinal characteristics.  On the other hand the Macristiidae are  similar to the Alepocephalidae i n many of the l i s t e d characters. Structure of the upper jaw and teeth, the slender branchiostegals, and the absence of scales agree with the Alepocephalidae.  In some  Alepocephalidae the ventrals are almost thoracic and the dorsal i s central i n position, thus approaching the Macristiidae.  140 Material examined:  None. Superfamily Clupeoidea Dussumieriidae P l . VI  Branchiostegals:  Vary from 6 to 20.  Gilchristella with 6 .  Spratelloides. Jenkinsia and  Gilchristella with 2 epihyal and 4 ceratohyal, 4  external and 2 ventral, branchiostegals spathiform with clupeoid Dussumieria with 12-20 with 3 i on the epihyal and 8-8^ on  projections.  the ceratohyal, a l l on the external surface.  Etrumeus with 13-15  bearing 4 on the epihyal and 9-10 on the ceratohyal, a l l on the external surface.  ^Histiothrissa with 15.  In Etrumeus most of the upper  branchiostegals are broad and spathiform and bear an anterior projection at the base. Operculars:  Opercular bones complete and entire.  G i l l membranes  separate. Hyoid arch:  Consists of interhyal, epihyal, ceratohyal and two hypohyals  in Etrumeus. Dusgumiera and G i l c h r i s t e l l a . In Dussumiera the epihyal possess a foramen and i t and the ceratohyal emit small prongs toward one another on their internal face. Relationships:  The more numerous branchiostegals of Dussumieriidae would  seem to indicate that i t arose off the primitive clupeid stock before the Clupeidae.  Chapman (1948a) agrees with this and adds several other  characters to confirm this view.  141 Spratelloides, Jenkinsia and Gilchristella differ from other dussumeriids by having only 6 branchiostegals instead of at least 14 or more.  The number of branchiostegals would appear to associate these  fish with the Clupeidae rather than the Dussumieriidae.  Spratelloides  further agrees with the Clupeidae and differs from the Dussumieridae in having two instead of only one supramaxillary.  Histiothrissa has too  many branchiostegals for the Clupeidae and too many supramaxillaries for  the Dussumieriidae; Arambourg (1954) has erected a special subfamily  for  i t in the Clupeidae.  References;  Chapman (1948a), Ridewood (1904a), Misra (1953), Munro  (1955), Schultz et al (1953), Weber and de Beaufort (1913), Whitehead (1962). Material examined;  Alizarin specimens of Gilchristella aestuarius, from  South Africa, NMC62-141; Dussumieria acuta, alizarin specimen, NMC63-71-S, Singapore; Etrumeus teres, alizarin specimen, NMC 63-70-S, Nagasaki, Japan. Engraulididae Branchiostegals:  Vary from 7-19, with 1-3 epihyal, 8 £ - l l ceratohyal and  4-10 external and 0-11 ventral.  Anchoviella 11-13, Setipinna 11-19,  Thrissocles 10-14, Scutengraulis 12-14, Anchoa IO-15, Coila 7-13, Stolephorus 11-13, Engraulis 9-14, Lycothrissa 7-12.  In Anchoa. compressa  10 with 1 epihyal and 9 ceratohyal, 10 external and one ventral, the uppermost broad and spathiform, the lovrer becoming narrower, a l l with a clupeoid projection. ceratohyal.  Engraulis encrasicholus 10 with 1 epihyal and 9  Coilia nasus 11 with 2g epihyal and 8^ ceratohyal.  Anchoa  142 hepsetus 15 v/ith 3 epihyal, 11 ceratohyal and 1 hypohyal, 4 external and 11 ventral, the upper ones broad and spathiform, a l l with a clupeoid projection on the base. Operculars:  Opercular bones complete and entire.  G i l l membranes  separate or joined and free from the isthmus. Hyoid arch: Consists of interhyal, epihyal, ceratohyal and two hypohyals in Anchoa. Engraulis, Coilia. Relationships:  The form of the branchiostegals indicates the Engraulididae  to be related to the Dussumieriidae. References:  Chapman (1944), Weber and de Beaufort (1913), Chevey (1932),  Ridewood (1904a), Day (1875), Smitt (1895), Misra (1953), Inger and Kong (1962). Material examined: Anchoa hepsetus. alizarin specimen, NMC62-73, North Carolina. ^ Clupavidae Branchiostegals: F i g . 1584 of Bertin and Arambourg (1958) shows Clupavus bears at least 4 spathiform branchiostegals. Operculars:  Opercular bone3 complete and entire.  Relationship:  According to Bertin and Arambourg may be placed i n the  neighbourhood of the Dussumieriidae. References:  Bertin and Arambourg (1958).  143  f Pseudoberycidao Branchiostegals: Opercularst  Information not available.  Operculum and suboperculum entire.  Relationshipst References;  Allied to the Clupeidae according to Berg.  Woodward (1901), Berg (1947). ^ Syllaemidae  Branchiostegals:  In fSyllaemu3 there are 10 delicate branchiostegals  rays on the ceratohyal. Operculars:  Complete and entire.  Relationship: References:  According to Berg they are allied to the Clupeidae.  Woodward (1902^12), Berg (1947). ^ Ichthyodectidae  Branchiostegals: Relationships:  No information available. According to Woodward (1901) the vertebral axis, fins  and scales are as in Chirocentrites. Chirocentridae Branchiostegals:  Vary from 6-8.  Chirocentrus with 6-8, with 2-3 on  the epihyal and 4-5 on the ceratohyal; the ones on the epihyal being on the external, those on the ceratohyal on the ventral face of the arch; the upper 2-3 spathiform, the lower scythe-shaped.  C. hypsoseloma with  144  6 and C. dorab with 8.  The uppermost with a clupeoid projection.  /Platinx with 6-7, ^Chirocentrites with about 20. Operculars;  Complete and entire.  G i l l membranes separate.  Hyoid, arch;  Consists of interhyal, epihyal, ceratohyal and two hypohyals,  ventral side of ceratohyal notched for reception of branchiostegals. Relationships:  The Chirocentridae differ from the Alepocephalidae and  Searsiidae by the breadth of the upper branchiostegals which are narrow in the other two families.  The f o s s i l Chirocentrites with 20  branchiostegals differs trenchantly from Chirocentrus with only 6-8. In fact i t might be suggested that i t does not belong in this family. Bertin and Arambourg (1958) have placed Chirocentrites in the family /ichthyodectidae.  This placement cannot be evaluated from the point of  view of branchiostegals since branchiostegals are unknown in the Ichthyodectidae. References:  Woodward (1901), Ridewood (1904a), Day (1875), Chevey (1932).  Material examined:  Chirocentrus hypsoseloma, alcoholic specimen, BC58-32,  from Malaya; Chirocentrus dorab, alcoholic specimen, USNM 47990, from Cochin China. Dorosomatidae Branchiostegals:  Vary from 5-6.  Dorosoma 5-6 with 1 epihyal and 4  ceratohyal, 3 on the external and 2 on the ventral face of the hyoid arch; the upper three branchiostegals broad and scimitar-like the lower two acinaciform.  The upper 3 have clupeoid projections at the base.  145 Nematalosa 6 with 1^ epihyal and l+h ceratohyal. Operculars:  Opercular bones complete and entire.  G i l l membranes  separate. Hyoid arch:  Consists of interhyal, epihyal, ceratohyal and two hypohyals.  Relationships:  Relationship to the Clupeidae, Engraulididae and  Dussumieridae is clearly shown by the possession of a clupeoid projection at the base of the upper branchiostegals. References:  Day (1875), Ridewood (1904a), Vladykov (1945).  Material examined:  Dorosoma cepedianum, alizarin specimens, NMC60-521-A,  from Lake St. Claire, Canada. Clupeidae P l . VII Branchiostegals:  Vary from 6 to 10 with 1^ - 3 epihyal and 4-8  ceratohyal, 3 external and 4-7 ventral.  In Alosa 7; Sardinpps 7 with I5  epihyal and 5z ceratohyal; Opisthonema with 6, 2 epihyal and 4 ceratohyal; Clupea harengus p a l l a s i i with 8-9, 2 epihyal, 7-8 ceratohyal, 3 external and 6-7 ventral; Corica, Clupeoides. Amblygaster, Pellona, Opisthopterus. Racqnda 6; Harengula 5-6; /scombroclupea, ^Diplomystus with about 10; Alosa pseudoharengus 7 with 2 epihyal and 5 ceratohyal, 3 being external and 4 being ventral, the ventral ones being inserted in notches. Opisthopterus dovi 6 with 2 epihyal and 4 ceratohyal, 3 external and 3 ventral.  In these genera the upper three branchiostegals are usually  wide and spathiform, the lower ones being slender.  An anterior projection  146 arises from at the base of at l e a s t the upper branchiostegal. /scombroclupea  according to Woodward's figure does not bear these  projections.  Operculars:  Opercular bones complete and e n t i r e .  G i l l membranes  separate. Hyoid arch:  Consists of interhyal, epihyal, ceratohyal and two hypohyals  i n Clupea, and Hyperlophus.  References:  Ridewood (1904a), Schultz et a l (1953), Fowler (1936), Day  (1875), Chapman (1944b), Misra (1953), Woodward (1901, 1902-12). Material examined:  Alosa pseudoharengus, one a l i z a r i n specimen,  NMC60-452-A, from Lake Ontario, Canada; Clupea harengus p a l l a s i i , 4 a l i z a r i n specimens, BC60-326, B r i t i s h Columbia, Canada; Opisthopterus dovi, alcoholic specimen, BC57-83, Bahia de Petacalco, Mexico. Denticipitidae Branchiostegals:  5 i n Denticeps clupeoides with 1 epihyal and 4 ceratohyal,  a l l external, the uppermost broad mesially, the central 3 slender, the lowest broad, with a clupeoid projection, and bearing denticles along i t s anterior edge (unlike any other clupeiform). ^Palaeodenticeps with 4 or 5, the upper 3 spathiform. Operculars:  Complete and e n t i r e .  In Denticeps operculum denticulate,  suboperculum small and edentulate, interoperculum elongate and denticulate; g i l l membranes separate.  In Palaeodenticeps suboperculum denticulate.  147 Hyoid arch:  In Ponticeps consists of interhyal, epihyal, ceratohyal and  two hypohyals.  The lower hypohyal large, the upper small and located  between the upper corners of the lower hypohyal and ceratohyal. Relationships:  The keeled ventral scutes on the belly, the connection  between the gas bladder and ear, and the clupeoid projection are a l l characters suggesting clupeoid relationship.  The reduction of caudal  rays to 16 from the normal clupeoid number of 17 may represent an adaptation to miniaturization. References:  Clausen (1959), Greenwood (I960).  Material examined:  Denticeps clupeoides, 1 alizarin and 2 alcoholic  specimens, uncatalogued NMC specimens from the Upper Yewa on the boundary between Nigeria and Dahomey, received through the kindness of Dr. Clausen; alcoholic specimen, USNM 195992, from Nigeria. Bathylaconidae Branchiostegals:  8 - 9 in Bathylaco, broad, curved, scythe-like with  bases bearing anterior projections. Operculars:  Complete and entire except for the posterior border of the  operculum which i s crenulate. Relationships:  G i l l membranes separate.  Goode and Bean (1896) f i r s t placed Bathylaco in the  Synodontidae of the Iniomi, probably largely on the basis of the elongate jaws and oblique opercular apparatus.  Parr (1948) included i t in the  Isospondyli and regarded i t as a possible intermediate between the Isospondyli and the Iniomi.  Bertin and Arambourg (1958) placed i t in a  148 new suborder, Bathylaconoidei, intermediate between the Stomiatoidei and the Esocoidei. The broadness of the branchiostegals differentiates the Bathlaconidae from the Myctophiformes and from any stomiatioid or esocoid.  The comma-  shaped preorbital photophore need not indicate relationship to the Stomiatioidei since a similar photophore has arisen independently in the Myctophiformes.  The anterior projections on the bases of the branchiostegals  in Parr's figure are suggestive of the clupeids and relatives.  Amongst  the clupeoids the engraulidids perhaps are the most similar with the narrow elongated tooth jaws, oblique suspensorium, and large anterior eyes.  The Bathylaconidae are provisionally placed in the Clupeoidei.  However, until specimens of Bathylaco are available for osteological study placement w i l l be uncertain. References:  Goode and Bean (1896), Parr (1948), Bertin and Arambourg  (1958), Jordan and Evermann (1896). Material examined:  None. ^ SUBORDER TSELFATOIDEI  Branchiostegals 13-14, with about 4 epihyal and 9-10 ceratohyal, a l l apparently on the ventral edge of the hyoid arch. branchiostegals spathiform, lower ones slender. present and entire; interoperculum not known. known.  No gulars.  Uppermost  Operculum and suboperculum Epihyal and ceratohyal  A single f o s s i l family.  The family Tselfatidae was found by Arambourg (1954) who placed i t in the Beloniformes.  Bertin and Arambourg (1958) erected a new suborder,  149 Tselfatoidei, for i t s reception in the Beloniformes. Several characters do not support this ordinal placement.  The  Tselfatidae has too many branched caudal rays (18 instead of 13), too many pelvic rays (7 instead of 6),  the dorsal and anal are very long  and high instead of small low and posterior, the parasphenoid i s toothed, the epihyal and ceratohyal are not sutured together, and the mouth i s bordered by both the premaxillary and maxillary. A l l of these characters preclude i t s placement i n the Beloniformes. The entrance of the maxillary into the gape would permit placement in Clupeiformes, Notacanthiformes, Mormyriformes, Cypriniformes or Anguilliformes.  The numerous caudal rays, normal anterior vertebrae,  toothed parasphenoid, presence of a supraorbital, and numerous distally spathiform branchiostegals preclude placement in any of these orders except the Clupeiformes.  A l l of the characters of the Tselfatidae are  readily accommodated in the Clupeiformes except the long pedicels of the premaxillaries. The premaxillaries are reported to have long pedicels which would indicate that they are probably protractile, a character normally acanthopterygian.  The majority of characters of the Tselfatidae  would appear to place them among the primitive Clupeiformes such as Albuloidei, Clupeoidei and Ctenothrissidae. / Tselfatidae Branchiostegals;  Tselfatia \idth 13-14  become spathiform dorsally.  slender branchiostegals which  About 4 epihyal and 9-10 ceratohyal,  distributed along the ventral edge of the hyoid arch. Operculars:  Operculum and suboperculum entire; interoperculum not known.  150 Hyoid arch;  ;  Only epihyal and ceratohyal known.  Epihyal and ceratohyal  not sutured together. References;  Arambourg (1954). Bertin and Arambourg (1958).  Material examined;  None.  ^ SUBORDER CTENOTHRISSOIDEI / Ctenothrissidae Branchiostegals:  Vary from 8 to 10 with 2 or 3 epihyal and 7 ceratohyal  in Ctenothrissa.  The upper branchiostegals are spathiform the lower  ones become narrow and acinaciform.  The uppermost branchiostegal has  anterior projection at the base. Operculars;  Complete and entire.  Relationships;  This group was f i r s t placed in the berycoids because of  i t s anterior pelvics. clupeoids.  Regan and Berg have grouped i t close to the  The jaw structure, number form and arrangement of the  branchiostegals agrees with this grouping.  Bertin and Arambourg (1958)  have placed the Ctenothrissidae in the Bathyclupeiformes, apparently on superficial agreements in body form and fin arrangement. cannot agree with this arrangement.  The author  The Bathyclupeidae have f i n spines,  ventrals with 15 rays, only one supramaxillary, and a perciform number, form and arrangement of the branchiostegals.  While on the other hand  the Ctenothrissidae lack fin spines, have two well developed supramaxillaries and have malacopterygian branchiostegals.  While i t is  possible that ctenothrissid-like ancestors could have given rise to the  151  bathyclupeids, the two families definitely do not belong in the same order or to the same level of evolution.  The Ctenothrissidae may be imagined  to have arisen off primitive clupeoid stock, developed a shortened deepened body and with this change more anterior pelvic fins and an enlarged dorsal f i n . References:  Woodward (1901, 1902-1912). ^ SUBORDER SAUR0D0NT0IDEI / Saurodontidae  Branchiostegals:  No information available.  Operculars:  Complete and entire.  References:  Newton (1878). SUBORDER HI0D0NT0IDEI, New Suborder  Branchiostegals 7-10, with 2-2^- epihyal and 6-7 ceratohyal, 4-5 on the external and 4-5 on the ventral face of the hyoid arch. Uppermost branchiostegals spathiform. entire.  G i l l membranes separate.  No gulars.  Opercular bones complete and  Two hypohyals.  One living family.  Regan (1929) placed the Hiodontidae in a superfamily with the Notopteridae, with which i t bears a superficial resemblance. followed Regan but raised the superfamily to a suborder.  Berg (1947)  Gosline (i960)  placed the superfamilies Hlodontoidae, Notopteroidae and Osteoglossoidae a l l in his division Osteoglossi of the Clupeiformes.  However, the  Hiodontidae would seem to be well separated from these groups, as i t is distinguished from them by the following trenchant characteristics: possession of two hypohyals instead of one; upper branchiostegals spathiform instead of acinaciform or virgaform; 8 hypurals instead of 4  152 or fewer; nasals small instead of l a r g e . to show that the Hiodontidae  A l l of these characters combine  i s d i s t i n c t from the notopterid-osteoglossid  group, and i s much more p r i m i t i v e . I t s o r i g i n appears to l i e v/ith the albuloids or clupeoid3.  As i n some clupeoids a duct from the gas bladder  contacts the inner ear.  I t d i f f e r s from clupeoids and albuloids however,  i n lacking oviducts, i n having the parapophyses c o o s i f i e d with the centra, and 16 branched caudal rays.  These characters j u s t i f y i t s sub-  o r d i n a l separation.^"  Hiodontidae  (Hyodontidae)  P l . VII Branchiostegals;  Vary from 7-10  i n Hiodon (including Amphiodon).  Hiodon tergisus 8-9 with 2 epihyal and 6-7  In  ceratohyal, 4 on the external  and 4*-5 on the v e n t r a l surface of the hyoid arch, the uppermost 2-3 branchiostegals spathiform and expand d i s t a l l y .  In Hiodon alosoides 7-  10, usually 9 with 2g epihyal and 6^ ceratohyal, 5 on the external and 4 on the ventral face of the hyoid arch. A pertinent paper has just been received i n f i n a l typing, Greenwood (1963). He r a i s e s Gosline»s Osteoglossi to o r d i n a l l e v e l . The author agrees with the separation of the Osteoglossi (except Hiodontidae) from the Clupeiformes. But t h i s author f e e l s the Osteoglossi are s u f f i c i e n t l y close to the Mormyriformes to be included i n them, thus a new order i s not necessitated. The Hiodontidae have numerous p r i m i t i v e characters which are l a c k i n g i n the Mormyriformes (as here construed) but which may be found i n the Clupeiformes that i t i s c l e a r they should be placed with the l a t t e r : 2 hypohyals, spathiform branchiostegals, gular f o l d , 8 hypurals, 3-4 uroneurals, adipose eyelid, postterminal centra, etc. S i m i l a r i t i e s of the Hiodontidae to the Notopteridae may e i t h e r represent parallelisms or be evidence of distant common ancestry.  153 Operculars;  Complete and entire.  G i l l membranes separate, with gular  fold. Hyoid arch:  Interhyal, epihyal, ceratohyal and two epihyals in Hiodon  tergisus. References:  Ridewood (1904), (1905b), Jordan and Evermann (1896),  Boulenger (1904). Material examined:  Hiodon tergisus, alizarin specimen, BC58-164 from  Lake Winnipeg, Manitoba; specimen BC60-250 from Lake Winnipeg, Manitoba; two alizarin specimens, NMC59-334 from Lac St, Pierre, Quebec.  Hiodon  alosoides, 1 alizarin and 10 alcoholic specimens from Saskatchewan River, Manitoba. SUBORDER G0N0RHYNCH0IDEI Branchiostegals 4-5, with 4 epihyal and 0-1 ceratohyal, a l l external, the upper 2 spathiform.  Opercular bones complete and entire.  membranes broadly joined to isthmus.  Two hypurals.  Gill  A single family,  Gosline (i960) united Berg's suborder Chanoidei, Phractolaemoidei, and Cromerioldei with the Gonorhynchoidei. At the same time he appeared uncertain that these groups belong together, "These five groups are so widely different that any relationship between them i s d i f f i c u l t to comprehend.  Yet the following similarities may be marshalled".  He then  l i s t s g i l l membranes always attached to isthmus (yet in Chanos they are united and free), the mouth small and toothless or nearly so, supramaxillaries absent, the preopercular border free only below (Chanos), i f at a l l , and several other characters.  In his key he characterizes the  154 suborder as having 3-4 branchiostegals, however, Gonorhynchidae have 4-5. This author agrees with Gosline that the Phractolaemidae, Kneriidae and Croraeriidae belong in the same suborder.  These families share 3  branchiostegals, about 5-9 pelvic rays, 34-45 vertebrae, absence of axillary appendages, absence of pharyngeal teeth, g i l l opening restricted, scales cycloid or absent, presence of a gas bladder, a similar caudal skeleton (Gosline) and are a l l small African freshwater fishes.  The  Chanidae share with these 45 vertebrae, absence of pharyngeal teeth, cycloid scales, a gas bladder, a similar caudal skeleton (Gosline), but they differ in having 4 branchiostegals, 11-12 pelvic rays, having axillary appendages, caudal f i n flaps, g i l l membranes united and free from the isthmus and being Indc—Pacific in distribution. are not too trenchant.  These differences  Further, Audenaerde (1961) i n his osteological  study of Phractolaemus states that numerous osteological and anatomical characters suggest a close relationship of Phractolaemus and Chanos. Gonorhynchidae shares only these characters:  pharyngeal teeth  absent, g i l l membranes joined to isthmus (but opening not restricted). It differs i n having 10 pelvic rays, 54-56 vertebrae, possession of axillary appendages, ciliated scales, gas bladder absent, a different caudal skeleton (Gosline) as well as in peculiar characters such as a median rostral barbel, tongue-like and fringed flap-like structures on the roof of the mouth, rounded basi-branchial teeth, posterior side of fourth g i l l and back of branchial cavity papillose, peritoneum black, thick l i p s , a pseudc—occipital condyle (Gregory, 1933), and others. dwells in the Indo-Pacific.  It  The characters shared with Chanidae are a  155 high number of pelvic rays, axillary appendages and number of branchiostegal rays (4 i n Chanidae, 4-5 i n Gonorhynchidae).  But while the branchiostegal  ray number i s similar, as noted by Gosline, they differ i n arrangement and form. only 2.  In Gonorhynchidae there are 4 on the epihyal, in Chanidae  Those i n Gonorhynchidae lack clupeoid projections, while those  of Chanidae possess clupeoid projections. The g i l l membranes differ and they differ i n the peculiar characters listed above. It i s concluded that Phractolaemidae, Kneriidae, Chanidae and Cromeriidae belong i n one suborder, the Gonorhynchidae require a separate suborder. Gosline (I960) stated that the caudal skeleton of Gonorhynchus bore considerable resemblance to that of Dus3umieria. The dussumieriids and alepocephalids are the only clupeoids with as many as 4 branchiostegals on the epihyal like Gonorhynchus. The albuloids would also form a possible ancestor i n the last respect, and somewhat resemble Gonorhynchus in dentition. Gonorhynchidae P l . VII Branchiostegals:  Vary from 4-5 i n Gonorhynchus. The upper two  branchiostegals broaden distally into a lamina and are more or less straight.  A ridge strengthens each of the branchiostegals.  4 branch-  iostegals on the epihyal and 0-1 on the ceratohyal, a l l on the external face of the arch. Operculars;  Complete and entire.  The operculum extends in a wedge down  into the suboperculum. The suboperculum extends more than half way up  156 the posterior border of the operculum.  G i l l openings wide, membranes  attached to isthmus. Hyoid arch:  Consists of large interhyal, epihyal, ceratohyal and two  hypohyals. References:  Hubbs (1920), Ridewood (1905a).  Material examined:  Gonorhynchus  gonorhynchu3,  alcoholic specimen,  USNM 59920 from New South Wales, Australia; G. gonorhynchus, alcoholic specimen, BC56-278 from New Zealand; G. gonorhynchus, alizarin specimen, NMC62-140, from South Africa. SUBORDER CHANOIDEI Branchiostegals 3-4 with 2 epihyal and 2 ceratohyal, a l l external, spathiform, with clupeoid projections at least in Chanidae. Gular absent. Opercular bones complete and entire.  G i l l opening restricted or g i l l  membrane united and free from isthmus (Chanidae). or one (Phractolaemidae).  Two hypohyals (Chanidae)  Four families.  The relationships of this suborder are discussed under the Gonorhynchoidei.  This suborder appears to be distinguished by the  absence of an interhyal.  But this is not yet verified in the Kneriidae  or Cromeriidae. Chanidae PI. VI Branchiostegals:  In Chanos 4 branchiostegals on each side, a l l broad  and spathiform but lower three tapering, bases broad with anterior clupeoid projection, 2 on epihyal, 2 on ceratohyal, a l l on external face  157 of hyoid arch Operculars:  Complete and entire.  operculum and suboperculum. Hyoid arch:  A straight border between the  G i l l membranes united and free from isthmus.  Consists of epihyal, ceratohyal and two hypohyals.  Interhyal  absent, epihyal connected to hyomandibular via ligament. Relationships:  The anterior projection on the base of the branchiostegal  i s similar to that in the clupeoids.  The reflexed basicranium of Chanos  i s much like that of the Dussumieridae. References:  Hubbs (1920), Day (1875), Jordan and Evermann (1896), Weber  and de Beaufort (1913), Ridewood (1904a). Material examined:  Chanos chanos, alizarin specimen, BC60-25, Mexico. Kneriidae  Branchiostegals: Operculars:  In Kneria 3 branchiostegal rays.  Complete and entire.  Operculum rounded posteriorly, sub-  operculum wedge-shaped, interoperculum elongate and expanded up around posterior border of preoperculum.  G i l l opening restricted to small  lateral s l i t . References:  Giltay (1934a), Hubbs (1920), Berg (1947).  Material examined:  None. Phractolaemidae  Branchiostegals:  3 slender in Phractolaemus.  158  Operculars;  Complete and entire.  The lower limb of the preoperculum is  much expanded and covers the elongate interoperculum, operculum oval, suboperculum wedge-shaped.  G i l l opening restricted and reduced to a  small s l i t on the side of the head. Hyoid arch;  Interhyal apparently absent, epihyal, ceratohyal and one  hypohyal present. Relationships:  Like Mormyriformes this family has only one hypohyal.  However, the opercular and caudal skeleton differ strongly indicating the loss of a hypohyal is only a parallelism. References;  Hubbs (1920), Audenaerde (1961), Ridewood (1905), Poll  (1957), Boulenger (1904). Material examined;  None. Cromeriidae  Branchiostegals;  3 curved scimitar-like branchiostegals which terminate  in a point, in Cromeria. Operculars:  Complete and entire.  Operculum an oval, suboperculum a  broad wedge, interoperculum elongate broadening posteriorly.  Gill  opening restricted to a small opening on the lateral surface. Relationships: related.  The Cromeriidae, Phractolaemidae and Kneriidae are closely  They share three branchiostegals, a laterally restricted g i l l  opening, a wedge-shaped suboperculum, an elongate interoperculum which broadens posteriorly plus characters previously mentioned.  Of the three  159 the Cromeriidae are the moat degenerate, having lost the scales, supraorbitals, suprapreopercular, etc. References:  Hubbs (1920), Gregory (1933).  Material examined:  None. SUBORDER ST0MIAT0IDEI  Branchiostegals 5-24 with 0-1 interhyal, 3-8 epihyal, 4-12 ceratohyal and 0-5 hypohyal, 3-12 external and 0-7 ventral. bones complete and entire.  Two hypohyals.  placed in the family.  Opercular  G i l l membranes separate, united and free  from isthmus or joined to isthmus. Sternoptychidae.  Gular absent.  Ceratohyal elongate, except in Nine families, one wholly f o s s i l , are  Two additional families, one f o s s i l are  provisionally included. The Rosauridae and Protostomiatidae are only provisionally placed in this suborder.  Their branchiostegal series do not confirm placement  here. The remaining families share characters with one another and appear to form a natural phylogenetic unit.  They are characterized by possession  of numerous branchiostegals; by expansion of the upper one or two branchiostegals (except in Idiacanthidae), the remainder being slender; by the branchiostegals usually extending onto the lower hypohyal; by the deep and narrow operculum; by the reduced suboperculum and interoperculum; by the thin and poorly ossified opercular bones; and by the photophores on the branchiostegal membrane. Tne high number of branchiostegals, elongate mouth, and deep operculum might lead one to conclude the stomiatoids were derived from  160 the Engraulididae. However, the stomiatoids have a higher number of branchiostegals on tho epihyal, making such a derivation unlikely.  The  high number of epihyal branchiostegals \rould be commensurate with derivation from the elopoids.  This contention is supported by Regan  (1923b) who found striking agreement in the skulls of Photichthys and Elogs. The unusual feeding mechanism of Chauliodontidae and Malacosteidae is described and illustrated by Tchernavin (1948), (1953) and Gunther and Deckert (1959). Gonostomatidae ( i n c l . Maurolicidae) Branchiostegals:  Vary from 7-21.  In Agyripnus 8-10, Bonapartia 11-16,  Cyclothone 10-14; Danaphos 9-10, Diplophos 11-14, Gonostoma 10-14, Ichthyococcus 11-12, Margrethia 13, Maurolicus 9-10, Neophus 7-8, Photichthys 20-21, Pollichthys 11-12; Sonoda 8, Triplophus 11-14, Valencienellus 9-10, Vinciguerria 10-12, Woodsia 17, Yarella 13-16.  In  Vinciguerria lucetia 12 on both sides, with 4 epihyal, 7 ceratohyal and 1 hypohyal, a l l external, the upper 2 broad and scimitar-like, the lower ones becoming progressively more rod-like.  Photophores occur on the  branchiostegal membranes of a l l genera. Operculars:  Complete and entire.  Operculum elongate and vertical,  suboperculum and interoperculum reduced to small lamina.  G i l l openings  wide, g i l l membranes separate. Hyoid arch:  Consists of Vinciguerria of interhyal, epihyal, long  ceratohyal and two hypohyals.  Arch connected to jaws by a membrane.  161 Relationships;  The maurolicine and related genera, sometimes separated  as a distinct family, have 7-10 branchiostegals, while the remainder have 10-21. This would support subfamilial recognition of the two groups. References;  Grey (i960).  Material examined: Vinciguerria lucetia, alizarin specimen, NMC61-195, from 900 miles west of Lower California. Sternoptychid ae P l . VII Branchiostegals:  Vary from 5 to 11.  In Argyropelecus 9, Polyipnus 9-11,  and Sternoptyx 5» Argyropelecus sp. with 10 branchiostegals, 3 epihyal and 7 ceratohyal, 3 on external and 7 on the ventral face of the arch; the uppermost i s a rounded triangle, the next two lathe-like but expanding distally, the remainder rod-like. i s expanded and wing-like.  In Sternoptyx the upper branchiostegal  The branchiostegal membranes bear photophores,  6 i n Polyipnus and Argyropelecus and 3 i n Sternoptyx. Operculars:  Complete and entire.  alizarin stain.  Bones thin, laminar and take l i t t l e  Opercular narrow and vertical, suboperculum and inter-  operculum small. G i l l membranes free from isthmus or attached, sometimes united and free from isthmus. Hyoid arch: Interhyal, long epihyal and ceratohyal, and 2 hypohyals present.  The ceratohyal i s bent i n the middle with the apex upwards i n  Arkyropelecus.  Arch connected to jaws by a membrane.  162 References:  Schultz (1961), Weber and de Beaufort (1913), Fowler (1936),  Garman (1899), Jordan and Evermann (1896), Gregory (1933), Misra (1953) Material examined: Argyropelecus sp., alizarin specimen, NMC61-184, from 400 miles off California. Stomiatidae Branchiostegals: Vary from 14-19. In Stomias 14-19, Stomloides 15• Operculars:  Complete and entire, g i l l membranes separate.  Hyoid arch: A membrane connects the lower jaw with the hyoid arch. Relationships:  Parr (1927) believed that the stomiatids deserved  separation from the other two groups of stomiatoids, the gonostomatid group and the melanostomiatid group.  This division i s not reflected i n  the branchiostegal series. References: Parr (1927), (1933), Weber and de Beaufort (1913), Maul (1956a), Regan and Trewavas (1930), Regan (1923).  '  Material examined: None. Chauliodontidae Branchiostegals:  Vary from 15 to 21 i n the genus Chauliodus. In  Chauliodu3 macouni 20 branchiostegals with 5 epihyal, 11 ceratohyal and 4 hypohyal, the uppermost expanded, the remainder lathe-like. Operculars:  Complete and entire.  Operculum narrow and vertical, sub-  operculum and interoperculum small. G i l l membranes free.  B  163 Hyoid arch;  Interhyal, long epihyal and ceratohyal, two hypohyals.  The  hyoid arch and tongue are free from the jaws at the sides, being attached to the symphysis only by an elastic ligament.  The resulting freedom  enables the jaws to be shot forward and upward, enabling prey to be more readily caught.  Tchernavin (1948, 1953) reports on this interesting  feeding mechanism. References:  Morrow (1961), Garman (1899).  Material examined: Chauliodus macouni. alizarin specimen, NMC61-192, from 200 miles off Washington. Astronesthidae Branchiostegals: Operculars:  In Astronesthes 14-24.  Complete and entire.  References: Fowler (1936), Gibba and Aron (I960), Maul (1956a), Weber and de Beaufort (1913). Material examined: None. Malacosteidae Branchiostegals:  Vary from 8-18.  In Malacosteus 8 short rod-like  branchiostegals; i n Aristostomias 18 with one on the interhyal, 5 on the epihyal and 12 on the ceratohyal, the upper two expanded slightly and lath-like, the remainder rod-like. membrane.  Photophores on the branchiostegal  164 Operculars:  Complete and entire.  Operculum narrow and vertical,  interoperculum and suboperculum small and covered by the preoperculum which extends back because of the prolongation of the jaw. G i l l membranes separate, not joined to jaws. Hyoid arch:  The hybid arch i s not connected to the front or sides of  the mandible except by the long slender protractor hyoidei so that the mandible i s completely free, hence the name loosejaws applied to the family.  Hyoid arch consists of interhyal, long epihyal and ceratohyal  and 2 hypohyals i n Aristostomias and Malacosteus. References:  Gunther, K. and Deckert (1959), Weber and de Beaufort (1913),  Fowler (1936), Regan and Trewavas (1930). Material examined: Aristostomias scintillans. alizarin specimen, NMC61-182 from 50 miles west southwest of Cape Flattery, Washington. Melanostoraiatidae PI. VI Branchiostegals: Vary from 10-22 with 0-1 interhyal, 3-8 epihyal, 4-10 ceratohyal and 0-5 ceratohyal. In Tac to stoma 13 with 5 epihyal, 6 ceratohyal and 2 hypohyal; i n Bathophilus flemingi 10 with 3 epihyal, 7 ceratohyal and 0 hypohyal, 3 external and 7 ventral; Bathophilus metallicus 12 with 3 epihyal, 9 ceratohyal and 0 hypohyal; Chirostomias pliopterus 22 with 8 epihyal, 10 ceratohyal, and 4 hypohyal;  Leptostomias  bermudensis 19 with 6 epihyal, 8 ceratohyal and 5 hypohyal; Echiostoma tanneri 15 with 6 epihyal, 4 ceratohyal and 5 hypohyal; Melanostomias spilorhynchus 13 with 4 epihyal, 5 ceratohyal and 4 hypohyal; Photonectes  165 dinema 15 with 5 epihyal, 6jj ceratohyal and 3h hypohyal; P. margarita 13 with 4 epihyal, 7 ceratohyal and 2 hypohyal; Flagellostomias boureei 16 with 4 epihyal, 8 ceratohyal and 4 hypohyal; Grammatostomias flagellibarba 13 with 5^ epihyal, b\ ceratohyal and 1 hypohyal; Eustomlas fissibarbis 16 with 5 epihyal, 8 ceratohyal and 3 hypohyal*  In  Bathophilu3 flemingi the upper branchiostegal expands into a lamina distally, the rest are lath-like; in Tactostoma macropus the upper one is expanded into an elongate triangle, the rest are styllform*  In  Flagellostomias and Photonectes the upper branchiostegal was branched, probably as a result of fusion of branchiostegals. Operculars;  Complete and entire.  Operculum elongate and vertical,  suboperculum and interoperculum small. Hyoid arch;  Consists of interhyal, epihyal, ceratohyal and two hypohyals  i* Bathophilus* Melanostomias. Photonectes and Tactostoma. 1  Arch attached  to mandibles by membrane. References;  Gunther (1887), Parr (1933), Beebe and Crane (1939), Regan  and Trewavas (1930). Material examined:  Bathophilus flemingi. alizarin specimen, NMC61-80,  off northern California; Tactostoma macropu3. alizarin specimen, NMC61-182, 50 miles west southwest of Cape Flattery, Washington. Idiacanthidae Branchiostegals:  Vary from 12 to 18 in Idiacanthus*  In Idiacanthus  fasciola 17 with 5 epihyal, 7 ceratohyal and 5 hypohyal, a l l long and slender, the upper most not expanded unlike the preceding stomiatoid  166 families Operculars;  Complete and entire.  Operculum elongate and vertical,  others small. Hyoid arch;  Consists of interhyal, long epihyal and ceratohyal and two  hypohyals (basihyal of Beebe). Relationship;  Arch attached to mandibles by membrane.  According to Beebe, closely related to the Melanostomiatidae.  Differs from other stomiatoids in the lack of an expanded upper branchiostegal. References;  Beebe (1934), Garman (1899), Gunther (1887), Weber and de  Beaufort (1913), Regan and Trewavas (1930). Material examined:  None. / Tomognathidae  Branchiostegals:  At least 7 in Tomognathus mordax, the dorsal one  spathiform, the remainder slender, with about 4-5 on the epihyal. Operculars:  Complete and entire.  Relationship:  Operculum deep and narrow.  The deep operculum, only the uppermost of the branchiostegals  spathiform, and the high number, 4-5 of the branchiostegals on the epihyal suggest that this family i s correctly placed in the Stomiatoidei. References:  Woodward (1902-1912), (1936).  167 ^ Protostomidae, incertae cedis Branchiostegals:  Vary from 10-24. In Protostomias about 24, short,  slender branchiostegals; in Pronotacanthus 10 slender branchiostegals with 4 epihyal and 6 ceratohyal. Operculars:  Complete and entire in Prostomias; the operculum sub-  triangular with the suboperculum curving up around posteriorly, the interoperculum a small triangle.  Operculum not deep and narrow in  Pronotacanthus. Hyoid arch;  At least a long epihyal and short ceratohyal in  Pronotac anthus. Relationships;  Arambourg (1954) removed Pronotacanthus from the  Notacanthidae and placed i t in the Stomiatoidei.  The operculum and jaw  apparatus of Pronot ac an thus or Prostomias does not agree with that in other stomiatoids where the operculum i s deep and narrow and the jaws and gape long making the suspensorium vertical.  The arrangement of  the branchiostegals, terminal mouth and absence of a "spinous" dorsal in Pronotacanthus exclude i t from the Notacanthiformes. References;  Arambourg (1954), Woodward (19d). Rosauridae, incertae cedis  Branchiostegals;  In Rosaura rotunda 10 long slender branchiostegals  which taper distally; about 4 epihyal and 6 ceratohyal;the uppermost i s bent into an S-shape. Known only from a postlarval specimen of 8.4  mm.  Branchiostegals extend out behind at right angle to the jaws, the rays continuing beyond the branchiostegal membrane.  168 Operculars:  Entire.  Operculum a vertically suspended oval, suboperculum  and elongate oval. Interop