238 COMPARATIVE ZOOLOGY OF CHORDATES 



Class. 

 Grade. 



Order. 



Order. 



Grade. 



Subclass. 



Subclass. 



Class. 



Order. 



Order. 



Order. 



Order. 



Grade. 



Class. 



Subdivision. 



Order. 



Order. 



Order. 



Order. 



Order. 



Subdivision. 



Class. 



Subclass. 



Pisces (Fish). With paired fins. 

 Chondrichthyes. With cartilaginous 

 skeleton only. 

 Selachii. Gills uncovered, 

 hyostylic or amphistylic, e.g. 

 Scy Ilium, sharks and rays. 



Holocephali. Pseud-autostylic, 

 e.g. Chimaera. 

 Osteichthyes. With bony skeleton, 

 lung or air-bladder. 



Teleostomi. With air-bladder, 

 hyostylic, e.g. Gadus (cod). 



Dipnoi. Lung used for breath- 

 ing, e.g. Ceratodus. 

 Amphibia. With an aquatic gill- 

 breathing larval stage followed 

 by a terrestrial air-breathing 

 adult. 



Labyrinthodontia (or Stegoce- 

 phalia). Primitive extinct 

 forms with a complete roofing 

 to the skull, e.g. Eogyrinus. 



Urodela. With a tail in the adult, 

 e.g. Triton (newt). 



Anura. Without a tail in the 

 adult, e.g. Rana (frog). 



Gymnophiona. Limbless, e.g. 

 Ichthyophis. 

 Amniota. Embryo develops on land 

 inside an amnion. 

 Reptilia. Body covered with horny 

 scales, cold-blooded. 

 Sauropsida. Reptiles related to the 

 birds. 



Chelonia. Body enclosed in a 

 carapace, e.g. Testudo (tor- 

 toises and turtles). 



Rhynchocephalia. Primitive 



forms, e.g. Sphenodon. 



T acertilia. Quadrate loose, e.g. 

 Lacerta (lizard). 



Ophidia. Both halves of lower 

 jaw loose, e.g. Vipera (snakes). 



Crocodilia. Heart 4-chambered, 

 e.g. Crocodilus. 

 Theropsida. Reptiles related to the 

 mammals. 

 Aves (Birds). With feathers, warm- 

 blooded. 



Palaeognathae. With a large pre- 

 vomer, e.g. Struthio (Ostrich). 



