352 



AMPHIBIA. 



of the dorsal vertebrae, and in the complicated structure of the 

 teeth. These last-mentioned organs are not only often very 

 numerous, but are of large size. The subjoined illustration 

 (fig. 310) shows the beautiful and complex structure of the 

 teeth, from which the name of the order is derived. 





Fig. 310. Section of the tooth of Labyrinthodon (Mastodonsaunts) Jtrgeri. 



The Labyrinthodonts range from the Carboniferous Rocks 

 to the Trias ; but some of the forms commonly included in 

 this order may perhaps belong elsewhere. One type of the 

 Labyrinthodonts is constituted by the singular genus Archcgo- 

 saurus, and the less known Apateon both from the Carboni- 

 ferous Rocks. Archegosaurus is remarkable in having the 

 notochord persistent, and in the possession of permanent bran- 

 chial arches. It has been made by Professor Owen the type 

 of a separate group, the Ganocephala ; but it is probably an 

 immature and larval form. The occipital condyles, also, do 

 not seem to have been ossified in the Archegosauria. 



Of the Carboniferous Labyrinthodonts the most important 

 genera are Anthracosaurus, Pholidogaster, Ophidcrpeton, Ich- 

 thyerpeton, Urocondylus, Lepterpeton, Baphctcs, Raniceps, Den- 

 drcrpeton, Hylcrpeton, and Hylonomns ; though the affinities of 

 some of these are more or less doubtful. Most of the Car- 

 boniferous Labyrinthodonts were of comparatively small size ; 

 but some, such as Baphetcs (fig. 311) and Anthracosaurus ', must 

 have attained gigantic dimensions. All the above-mentioned 

 genera seem to have possessed well-ossified vertebras, with well- 

 developed limbs, the form of the body being mostly salaman- 

 driform, but sometimes fish-like, or serpentiform. 



