474 THE MAMMALIA OF THE UINTA FORMATION. 



?MiAcis vuLPiNus S. & O. (Syn. ? AmjjMcyon vulpinum S. & O., No. 17, p. 

 255). Since our preliminary acconnt was written we have had the opportunity of 

 examining various specimens of Amphicyon, which show that our tentative reference 

 of the Uinta species to that genus must have been incorrect. It is equall}' clear that 

 the species cannot belong to Cynodictis, or to any of the flesh-eaters known to occur 

 in the White River beds, whereas it may very well be a species of Miacis, and in 

 view of the similarity of the Uinta fauna to that of the Bridger, this will probabl}' 

 turn out to be the case. The specimen consists of an isolated inferior premolar and 

 first molar. 



The premolar, probably the third, consists of a high, acute and compressed cone, 

 with rudimentary posterior heel ; a cingulum runs entirely around the crown and is 

 most conspicuous on the anterior surface. The principal cusp is not complicated by 

 the development of accessory tubercles upon it. The sectorial is canine in appear- 

 ance; the anterior portion consists of three cusps arranged in the ordinary triangle, 

 of which the external is the larger and flattened on the outer side ; the anterior cusp 

 is still very low and the sectorial blade is therefore much less completely developed 

 than in Cynodictis and hardly more so than in the Bridger species of Miacis. The 

 heel of the sectorial is low and small and not very distinctly basin-shaped. 



RODENTIA. 



PLESTARCTOMYS Bravard. 



Of all the rodents of the American Eocene, this genus is by fai' the most abund- 

 ant and characteristic, being found in all of the formations above the Puerco, which 

 indeed has hitherto yielded no I'odents at all. 



This genus has been defined by Cope (No. '3, p. 175-G) as follows: "The crowns 

 of the inferior molars suppoit four rather small anil strictly marginal tubercles, which 

 inclose a median valley. The anterior inner tubercle is more elevated than the others, 

 and the posterior two tubercles are connected by a low ridge on the posterior border, 

 which may be more or less tubercular on the last molar. In some of the species the 

 marginal tubercles are merely elevations of the margin, while, in others, the adjacent 

 tubercles of a pair approximate, so as to form a pair of interrupted cross-crests. 



" There are five superioi- molars, of which the anterior is of small size. They 

 resemble those of Sciurus, but the transverse crests are obsolete or wanting. The 

 l)ositions corresponding to their exU/rual extremities are maiked by more or less dis- 



