VfeilTEBRATE FAUNA OF THE BLANCO BEDS. 63 



short acute blade. Fourth inferior premolar present, one rooted. Third 

 inferior premolar molariform. 



This genus is established to receive a remarkable species of carnivore 

 from the Blanco terrane. The typical individual of the typical species is 

 represented by an anterior part of the lower jaw. Probably the same 

 species is represented by the separate crowns of two inferior premolars and 

 sectorial molar and some other fragments. These teeth are closely sim- 

 ilar to those of the existing Hyaenas, so that I refer the genus Borophagus 

 to the Hyaenidae provisionally, since the essential diagnostic parts have 

 not yet been found. The conic character of the principal premolars, and 

 their abrupt increase in size anteriorly, the low, almost molariform, char- 

 acter of the third premolar, together with the short blade of the inferior 

 sectorial, constitute strong points of resemblance to the Hyaenas. I re- 

 fer the present form to a distinct genus, under the name Borophagus, on 

 account of the pi'esence of the fourth premolar. 



In the Loup Fork epoch, the genus ^lurodon was repi'esented by sev- 

 eral species, varying from the size of a red fox to that of a grizzly bear, 

 which performed the function of Hyaenas in the economy of the fauna, in 

 devouring the carcasses of the numerous large species of Mammalia with 

 which they were contemporary. The premolar teeth of the larger spe- 

 cies were more robust than in the true dogs, and were useful in breaking 

 bones. In the Blanco fauna the genus Borophagus probably performed 

 the same function, and they carried the development of the premolar 

 teeth to a greater degree of effectiveness, as a mechanism for crushing 

 bones. They resemble those of the Hyaenas much more nearly than do 

 those of the species of ^lurodon, and were as robust as those of the 

 largest species of that old world type. 



On a former occasion, in discussing the affinities of the extinct dogs of 

 North America,* I expressed the view that the genus -3Elurodon would 

 prove to be the ancestor of the Hyaenidae. At that time no genus of 

 Hyaenidae was known from North America, and the genus JElurodon is 

 not known from the old world. The transition I suggested might have 

 been accomplished through the old world genera Ictitherium, and Hyae- 

 nictis, which have been regarded as transitional between the Viverridae 

 and Hyaenidae by Gaudry. It seems, however, that the American conti- 

 nent possessed in Borophagus a representative of Hyaenictis, with which 

 it agrees in possessing the fourth premolar. Dr. Schlosser has agreed with 

 my view that ^lurodon is probably ancestral to the Hyaenidae. This 

 hypothesis is, however, provisional only. 



♦American Naturalist, 1883, p. 224. 



