Peterson: Miocene Beds of Nebraska and Wyoming. 47 



American Museum of Natural History P-i and the nasals show very close 

 similarities to those of the type specimen in the Yale Museum. The 

 specimen in the American Museum is further distinguished from the 

 type of Diceratherium niobrarense by the less convex contour of the 

 skull from side to side, the smaller brain case and occipital condyles, 

 the more complicated grinding surfaces of the teeth, and by a small 



Fig. II. Posterior view of skull of Diceratherium niobrarense. \ nat. size. 

 Type, No. 127 1. 



tubercle in the median valley on the internal side of M-^. The type 

 of D. niobrarense and the specimen in the American Museum referred 

 to D. nanum are very nearly of the same size. The type of D. arma- 

 tum represents an animal of larger size, and there are other differences 

 which were pointed out by Marsh (Am. Jour. Science (3), Vol. IX, 

 p. 242, 1875). 



Diceratherium cooki Peterson. 



(Science, Vol. XXIV., No. 609, pp. 281-282, 1906.) 

 (Plate XV.) 



The modification of the teeth and the general construction of the 

 skull of this species at once separates it from other American species. 

 The European species Diceratherium minimum Cuvier is perhaps the 

 most nearly allied. It is interesting to note that the configuration of 

 the triturating surfaces of the teeth in Diceratherium nanum is more 

 nearly similar to the present species than to Diceratherium niobrarense 

 and Diceratherium ai'matum, and that the two latter have the teeth 

 complicated in nearly the same degree. 



