238 



University of California Publications. 



[Geology 



M 2 , anteroposterior diameter 



Mo, greatest transverse diameter 



No. 10651 



11.5 mm. 

 6.9 



In its most distinctive characters, that is in the form of M t 

 and M.,, this species resembles the typical Tephrocyon, and is 

 evidently closely allied to it. It differs from the type species in 

 the simpler premolars, larger metaconid of M lt and relatively 

 larger M 2 . The simplicity of the premolars, if found to occur 

 regularly in a large series of specimens, might, taken with other 

 differences, be advanced as evidence of subgeneric separation. 

 It should, however, be noted that on one specimen, no. 11474, a 

 distinct posterior cusp is developed on P 2 , though the dentition 

 is otherwise quite similar to the type specimen of T. kelloggi, 

 and there seems hardly sufficient reason for specific separation. 



The characters of the dentition in Tephrocyon as represented 

 in T. kelloggi are in some respects quite bear-like. The second 

 molar is unusually large, its anteroposterior diameter equalling 

 over seventy per cent of that in M x . The anteroposterior diam- 

 eter of M 2 nearly equals that of the corresponding tooth in T. 

 rurestris, while in that species the carnassial is one-third larger 

 than in T. kelloggi. In the carnassial the large heel and the 

 extraordinarily developed metaconid give an unusual crushing 

 surface. Judging from the size of the alveolus M 3 was relatively 

 larger than in T. rurestris. 



Such ursine characters as appear in the dentition of this form 

 are probably not to be considered as indicating' that it is in any 

 sense ancestral to the bears. The great variety of canids with 

 bear-like characters which is being found in the middle Ter- 

 tiary faunas does, however, suggest the possibility of independent 

 origin of certain of the groups which have been brought together 

 in the Ursidae. 



Occurrence: Virgin Valley Beds; locality 1065, Virgin Val- 

 ley, Humboldt County, Nevada. 



A single second lower molar of Tephrocyon (no. 12542, fig. 

 7) was found in the beds at Thousand Creek. This specimen 

 very closely resembles M 2 of the type specimen of T. kelloggi, 



TEPHROCYON, near KELLOGGI, n. sp. 



