1916] 



Merriam: Relationship of Equus to PUohippus 



527 



relatively simple characters. It is interesting to note in this connec- 

 tion that the peculiar characters of Cope's Equus simpHcidens fur- 

 nished some of the most important evidence used in determining the 

 age of the Blanco beds. 



The upper cheek-teeth of P. proversus (figs la to 4), as well as of 

 the P. simplicidcns and P. cumminsii types, are distinguished from 

 those of PUohippus as represented in the typical form, P. pernix, by 

 straighter crowns, with heavier mesostyle ; tendency to narrowing of 



Figs, la to 4. PUohippus proversus, n. sp. From the upper Etchegoin Plio- 

 cene of the North Coalinga region, California Figures approximately natural size. 



Figs, la, lb, and lc. P 3 ?, no. 22328; fig. la, occlusal view; fig. lb, outer view; 

 fig. lc, posterior view. 



Fig. 2. M 1 or M 2 , no. 21330, type specimen, occlusal view. 



Fig. 3. P 1 ?, no. 21331, occlusal view. 



Fig. 4. Portion of an upper cheek-tooth, no. 22329, occlusal view; p, proto- 

 cone; /, prefossette. 



