284 



CLASSIFICATION OF VERTEBRATES. 



ORDER III. STEREOSPONDYLI. 



Vertebrae amphicoelous, occipital region ossified, teeth 

 labyrinthine. GASTROLEPIDOTI. With ventral elongate scales. 

 Baphetes (coal, Nova Scotia), Platyops (Permian of Europe). 

 LABYRINTHODONTID^E, no ventral scales. Trematosaurus, Laby- 

 rint/wdon, Mastodonsaurus, etc., Europe. 



Jfa. 



FIG. 282. Skull of stegocephal, Trematosaurus,irom. Huxley. EpO, epotic; 

 Fr> frontal ; Ju, jugal ; La, lachrymal; Mn, mandible (of several bones); Mx^ 

 maxilla; Na, nasal ; Or, orbit; Pa, parietal; Pmx, premaxilla; Prf, prefrontal; 

 Ptf, postf rental; PtO, postorbital; Qt\ quadrate jugal ; SO, supraoccipital ; Sq, 

 squamosal ; St, supratemporal. The grooves shown were for lateral line organs. 



SUB-CLASS II. URODELA. (GRADIENTIA.) 



Amphibia with persistent tails ; usually two pairs of limbs ; 

 skull without ethmoid, supraoccipital, postorbital, or supra- 

 temporal ; no parietal foramen. Vertebrae amphicoelous, never 

 embolomerous or rhachitomous. Skin naked. 



ORDER I. PERENNTBRANCHIATA (PHANEROBRANCHIA). 



With persistent, bushy, external gills and gill slits ; maxilla 

 usually lacking; teeth on vomers and palatines. SIRENID^E, hind 



