Marsh Collection, Peabody Museum. 447 



different. In this species of Uintaoyon the heel is smaller, 

 and is composed of a single median cutting ridge, which is 

 highest behind. On the inner border the cingulum is very slightly 

 elevated, giving a faint indication of the basin of Vulpavus, but 

 this is so inconsiderable that the heel may be said to be cut- 

 ting. The second inferior molar, figures 12 and 13, may be 

 described as having a very reduced trigon with the anterior 

 cusp obsolete, a very small internal cusp and a cutting heel. 

 As compared with that of Vulpavus, the cusps are much 

 lower and more obtuse. The last molar is not preserved in 

 the specimen under discussion, but judging from the type 

 specimen it was small and single-rooted, with the cusps more 

 or less vestigial. 



The crown of the first superior molar, figure 15, in its exter- 

 nal part, bears a very striking resemblance to that of Vulpavus, 

 but internally, the two are quite distinct. As in that genus, 

 the antero-external angle is produced and formed into a sharp 

 cutting blade, separated from the antero-external cusp by a 

 deep slit-like notch ; this blade, together with the sharp ante- 

 rior transverse ridge, bites effectively against the shears of the 

 posterior cusps of the trigon. The postero-external angle is 

 rounded. Between the base of the external cusps and the 

 outer border of the crown is a relatively broad area, the outer 

 edge of which is occupied by the cingulum. The external 

 Cusps have a flattened conical form, the edges of which are 

 sharp, the anterior being the larger and more prominent of 

 the two. The internal cusp is more or less conical and is 

 somewhat extended posteriorly ; it is connected with the 

 antero-external cusp by a sharp transverse ridge, which is 

 interrupted near its middle portion by a distinct anterior inter- 

 mediate cusp. The posterior transverse ridge, which is very 

 generally present in tritubercular teeth of this character is 

 entirely absent. The cingulum, although more or less distinct 

 upon the inner face of the crown, does not develop any 

 postero-internal cusp. 



The jaw is moderately long, rather shallow vertically, and 

 of somewhat more than average thickness transversely. It 

 has a distinctive breadth and "square-cut" appearance of the 

 symphyseal region which is not shown in Vulpavus. 



I give the following measurements : 



% mm. 



Length of Pm. F , m. T , Y _ 15*5 



Length of inferior sectorial _- — 6* 



Width of inferior sectorial 4* 



Length of second molar - _ 4*5 



Depth of jaw at anterior border of sectorial 9*5 



Depth of jaw at posterior border of Pm. T 8* 



Thickness of jaw at posterior border of Pm. T 4- 



