O. G. Marsh — Notice of New Fossil Mammals. 327 



the skull of Brontotherium, but may be readily distinguished 

 from it by the dental formula, which is as follows : 



Incisors f ; canines \ ; premolars f- ; molars f . 



The presence of four premolars in each ramus of the lower 

 jaw is a distinctive feature in this genus. This character, with 

 the single, well-developed incisor, marks both the known 

 species. 



The type species here described is one of the largest of the 

 group, and the skeleton on which it is based is already repre- 

 sented on many plates of the monograph in preparation. The 

 skull is about thirty -two inches (81 cm.), in length, and twenty- 

 six and one half inches (67 cm.), across the zygomatic arches. 

 The pelvis is over four feet (120 cm.), in width. 



This unique specimen was discovered by the writer and H. 

 C. Clifford, his guide, in 1874, near the White River in north- 

 ern Nebraska. The geological horizon is in the upper part 

 of the Brontotherium beds of the Lower Miocene. 



Fig. 5. 



Fig. 6. 



Figure 5. — Skull of Brontops dispar, Marsh ; side view (young male). 

 Figure 6. —The same skull; top view. 



Both figures are one-eighth natural size. 



