422 University of California Publications in Geology [Vol. 7 



shelf of the cingulum extending around the anterior and inner 

 sides and into the hypostyle region posteriorly. On Dm 3 the 

 (unguium is faintly interrupted on the inner side opposite the 

 middle of the protocone, and fully interrupted on the inner side 

 of the hypocone. 



Figs. la and 1ft. Hypohippus (Drymohippus) nevadensis, n. sub-gen. 

 and n. sp. Upper milk molars. No. 21056, natural size. Fig. la, lateral 

 view; fig. lb, occlusal view. Stewart Valley Beds, southwestern Nevada. 



The principal difference between the Nevada specimen, no. 

 21056, and Hypohippus osborni is found in the separation of 

 the outer end of the metaloph from the ectoloph. In none of the 

 milk molars of the Nevada specimen is the summit of the outer 

 end of the metaloph connected with the ectoloph. In Dm 2 and 

 Dm 3 the base of the metaloph barely reaches the base of the 

 ectoloph. In Dm 4 the base of the metaloph scarcely reaches the 

 base of the ectoloph. In each of these teeth there is a small 

 transverse ridge or tubercle pointing inward from the ectoloph 

 at the posterior end of the paracone crescent. This transverse 



