282 



University of California. 



[Vol. 3. 



facts suggest that, while we may show that the two forms are 

 clearly related, we are not in a position to demonstrate generic 

 identity. The Calif ornian specimen represents a more extreme 

 form coming probably from Quaternary beds, while Borophagus 

 is Pliocene; the two occur at localities geographically distant 

 from each other; and we do not know the most essential parts of 

 the structure of Borophagus. 



The genus Borophagus was referred provisionally to the 

 Hyaenidae by Cope, and the general form of the mandible in 

 HyaenognatJms reminds one very much of that family. The 

 dentition of Hyaenognathus has, however, no real structural 

 resemblance to that of the hyaenas, though its functions were 

 evidently similar. This genus represents a type analogous to 

 the hyaenas, but is derived from a different source and worked out 

 (in a very different type of tooth structure. It represents the 

 extreme of known specialization of the dog family in one 

 direction. 



The genus differs so far from any known form that its 

 affinities are not clearly shown. It resembles the Amphicyonine 

 canids in the heavy jaw and simple premolars, but differs greatly 

 in the characters of the tubercular molars and of the heel of Mi . 

 Also, Pt, although simple, does not correspond to any form 

 found in the Amphicyonines. The genus Oephalogale, a somewhat 

 primitive form referred by Zittel to the Simocyoninae, presents 

 many points of resemblance, though it is separated by differences 

 of the same nature as those just mentioned. A similarity to the 

 Mustelines of the Gfulo group is presumably only superficial. 



Professor Cope evidently judged Borophagus to be derived 

 from the peculiar aberrant Aelurodons of America. They 

 resemble Hyaenognathus in possessing heavy jaws and heavy 

 premolars, in the reduction of the tubercular molars, and in the 

 reduced talon and metaconid of Mr. There are, however, four 

 premolars in Aelurodon, three of these having accessory cusps, 

 and the degree of modification required to produce from them a 

 premolar dentition like that of Hyaenognathus would be very 

 considerable. 



The true affinities of this form can be determined with 

 satisfaction only when we know more of the dentition and when 



