288 PROSAURIA 



sake, it be assumed that the iutercentral discs of Diplovertehron 

 and Gricotus are formed by the fusion of Amphibian interdorsals 

 with interventrals. Anyhow, simply to state that the tripartite 

 vertebrae of Eryo'ps are the same as those of Actiyiodon, 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 Keptiles are made up of basidorsals + 

 basiventrals + interventrals. (Cf. Fig. 56, p. 283, and Fig. 1, 

 p. 13.) 



Sub-Class II.—PEOSAUBIA. 



Mostly extinct Reptiles, luith decijly o.m'pMcoelous hut stereo- 

 spondyloiis vertebrae, vjith 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 veyitral side aiid ivith 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 ^ 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. 



Considering; the age of these little creatures and their low 

 position in the reptilian scale — in fact, they stand almost as low 

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



