284 



CLASSIFICATIOX OF VERTEBRATES. 



ORDER III. STEREOSPOXDYLI. 



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- 

 rintJwdon, Mastodonsanrus, etc., Europe. 



SJi 



Fig. 282. Skull of stegocephal, Trematosaurus, from Huxley. EpO, epotic; 

 Fr, frontal ; yii, jugal ; La, lachrymal; Mn, mandible (of several bones); J/.r, 

 maxilla; A'a, nasal; Or, orbit; Pa, parietal; Pmx, premaxilla; /"r/", prefrontal; 

 Ptf, postfrontal; PtO, postorbital; ^;, quadratojugal ; SO, ?upraoccipital; 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. PEREXNIBR.A.N'CHIATA (PHAXEROBRANCHIA). 



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

 usually lacking ; teeth on vomers and palatines. Sirenid.e, hind 



