Probably several other genera of American Permian and also of European Permian strata will, when better known and critically examined, have to be referred to the Proreptilia. Thus for instance the European _Melosaurus_ may have affinities with _Eryops_, while _Diplovertebron_ of Bohemia seems to be allied to _Cricotus_. The difficulty of division will lie with those Lower Permian Amphibia which, like _Archegosaurus_, _Euchirosaurus_, _Actinodon_, possess tripartite vertebrae, which at first sight are strikingly like those of _Eryops_. But the tail-vertebrae permit of no mistake, and since these are quadripartite in _Archegosaurus_, _Chelydosaurus_, and _Sphenosaurus_, these genera are safely to be classed with the Amphibia, unless, indeed, for mere argument's {288}sake, it be assumed that the intercentral discs of _Diplovertebron_ and _Cricotus_ are formed by the fusion of Amphibian interdorsals with interventrals. Anyhow, simply to state that the tripartite vertebrae of _Eryops_ are the same as those of _Actinodon_, would be as convincing as saying that the English and French flags are essentially the same, both containing the same colours, but one is white, red, and blue, the other blue, white, and red. Tripartite Amphibian vertebrae are composed of basidorsals + basiventrals + interdorsals, those of Reptiles are made up of basidorsals + basiventrals + interventrals. (Cf. Fig. 56, p. 283, and Fig. 1, p. 13.) _SUB-CLASS II.–PROSAURIA._ _Mostly extinct Reptiles, with deeply amphicoelous but stereospondylous vertebrae, with movable chevron-bones in the tail and frequently with intercentra in the trunk._ Sphenodon, _the only recent genus, has no copulatory organs_. ORDER I. MICROSAURI. _Extinct, small Reptiles, mostly Carboniferous and Permian, with dermal armour on the dorsal and ventral side and with bifurcated ribs._ We retain this term of Dawson's for those small, newt-shaped, chiefly Permian reptiles, which are allied to _Hylonomus_, after elimination of contemporary forms like _Keraterpeton_ and _Urocordylus_, which belong to the Branchiosaurian order of the Stegocephali. Until recently[122] all these creatures had been classed with the Stegocephali. The Microsauri in the present restricted sense reveal themselves, however, as reptiles by the movable chevron-bones in their tail, their broad neurocentral sutures, the possession of two sacral vertebrae (_Petrobates_), the bifurcated ribs which always articulate with the centra (most clearly shown in _Orthocosta_), and the possession of five fingers and toes.