144 THE ANATOMY OF VEKTEBRATED ANIMALS. 



scales, or is naked. The ventral fins, if present, are jugular in 

 position. The fin-rays are all articulated. The inferior pharj'n- 

 geal bones are distinct. ( Ophidini, Gadoidei, Pleuronectklce. ) 



The Pleuronectidm are ihe most aberrant of all Teleostean 

 fishes, on account of the disturbance in the bilateral symmetry 

 of the body, skull, and fins, to which reference has already 

 been made (p. 30). 



3 The Acanthopteri have generally ctenoid scales, thoracic 

 or jugular ventral fins, entire fin-rays in some of the fins, and 

 distmct inferior pharyngeal bones. The Percoidei, Cata- 

 phracti, Sparoidei, Scicenoidei, Labyriiithici, Mugiloidei, iVb- 

 tacanthini, Scomberoidei, Squamipennes, Tcenioidei, Gobioi- 

 dei, Plennioidei, Pediculati, Theuthyes, and Fistulares, be- 

 long to this great group. 



4. The Pharyngognathi is the name given by MuUer to a 

 somewhat artificial assemblage of fishes, the only common 

 characters of which are the anchylosis of the inferior pharyn- 

 geal bones and the closed pneumatic duct. They have either 

 c}'c"loid or ctenoid scales. The ventral fins may be abdominal 

 or thoracic. The anterior dorsal and ventral fin-rays may be 

 either unjointed, as in the Labroidei, Pomacentridm, Chro- 

 m idcB ; or articulated, as in the Scomberesoces. 



The two remaining groups are very peculiar ; but I con- 

 fe.ss I do not see upon what ground they can be regarded as 

 of ordinal value. 



5. The ZiophobrancMi. — The body is covered with bony 

 plates. The ventral fins are almost always absent. The infe- 

 rior pharyngeal bones are distinct. The branchial processes 

 have a clavate form, being larger at the free than at the at- 

 tached ends, and are in this respect unlike those of any other 

 fishes. {PegasidoB, Syngnathidce.) 



6. The Plectognathi. — The body is covered with plates or 

 spines. The ventral fins are absent^ or represented only by 

 spines. The inferior pharyngeal bones are distinct. The pre- 

 maxillse and, usually, the hyomandibular, are immovably united 

 with the skull — a character of rare occurrence among other 

 fishes. ( Gymnodontidm, Ostraciontidm, Palistidw.) 



The greater number of Teleostei are marine. No Anacan- 

 tliini, Plectognathi, or ZjophobrancJiii, and only one family of 

 Pharyngognathi (the Chromid(B), inhabit completely fresh 

 water. Comparatively few Acanthopteri are fluviatile. On 

 the other hand, by far the greater number of the Physostomi 

 are, either temporarily or permanently, fresh-water fish. 



If the JjeptolepidcB {Thrissops, Zeptolepis, Tharsis) are 



