The two genera _Eryops_ and _Cricotus_ of the North-American Permian formation had until recently[120] 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 Reptiles 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 Reptiles 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 temnospondylous, that the change from Amphibia into Reptiles 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 importance since we have known the condylar modifications of the Theromorpha; 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. {286}Until more genera are better known than they are now, it is premature to divide the present sub-class into orders. [Illustration: FIG. 57.–Trunk vertebrae of _Eryops_ (cf. Fig. 56, 4, p. 283). _Cp_, Articular facet of the capitulum of a rib.]