PLIOHIPPUS. 



171 



Affinities. — (Merriam, 191G, p. 530) The resemblance of the lower cheek teeth to those of P. simplicidens of the 

 Blanco may separate this species as a group distinct from the typical Pliohippus. There are evidences that P. proversus 

 may be derived by modification from one of the early Pliocene Pacific coast species near P. tantalus or P. fairbanksi. 



P. proversus shows nearest affinities among the Equus species to E. occidental-is of the California Pleistocene and to 



Fig. 137. Original figures of the type of Pliohippus proversus Merriam, Univ. Cal. Pal. Coll. 21330, m 1 or nr, 

 and of the upper grinding teeth of the paratype and referred specimens. (2) Occlusal view of 21330, type; (3) p 4 ?, occlusal 

 view of 21331 ; (4) portion of an upper cheek-tooth, 22329, occlusal view; ( la, lb, lc) occlusal, outer, and posterior views of 

 2232S, p 3 ?. Figures approximately natural size. After Merriam, 1916, p. 527. 



E. stenonis of the Old World Upper Pliocene. There is little doubt that P. proversus of the Etchegoin and P. simplicidens 

 and P. cumminsii of the Blanco represent closely allied forms of nearly the same epoch. The evidence indicates that 

 some at least of the Equus species of the American continent were derived from Pliohippus along the line of evolution 

 passing through or near the P. proversus group. 



