CHAPTER YIII 



PROREPTILIA I'KOSAURIA I'HEROMOJiPIIA 



Sub-Class I.—PEOBEPTILfA. 



Permian Temnospondylous Beptiles vnth well-developed limbs 

 and girdles of the terrestrial type. 



The two genera Eryops and Cricotus of the North-American 

 Permian formation had until recently ^ been relegated to the 

 Stegocephali. By grouping them and their nearest allies 

 together as Proreptilia it is intended to indicate that they are 

 the lowest known Eeptiles and that they probably link this class 

 to the Amphibia. The superficial resemblance of their tri- or 

 bi-partite vertebrae, and their occurrence in the Lower Permian, 

 have caused the error of classing them with the Stegocephali, but 

 the composition of their typically gastrocentrous vertebrae leaves 

 no doubt as to their affinities. After all, we feel certain that 

 Eeptiles have arisen from Stegocephalous Amphibia, and it is in 

 the Lower Permian, exactly where these debatable creatures lived 

 side by side with Stegocephali, undoubtedly likewise temnospon- 

 dylous, that the change from Amphibia into Eeptiles seems to have 

 taken place. Both are referable to Amphibia with (quadripartite 

 vertebrae. The condition of the occipital condyles determines 

 nothing. This greatly exaggerated character has lost in import- 

 ance since we have known the condylar modifications of the Thero- 

 morpha ; moreover, Cricotus itself seems to have possessed a single 

 condyle. We should even expect the Proreptilia to present 

 many Stegocephalous inheritances, for instance the condition of 

 the skull roofed in by dermal bones, a ventral dermal armour, a 

 very complete pectoral arch still without a sternum, and only one 

 sacral vertebra. 



1 Phil. Trans. cLxxxvii. 1896, B. p. 23. 



