Vol. (3 J Merriam: Virgin Valley and Thousand ('reek. 273 



Two upper premolars are present. The smaller one (a, fig. 

 53) is nearly triangular in cross-section. It supports a large 

 external and a slightly swollen internal tubercle. There is a 

 minute median anterior tubercle, but otherwise the cingulum is 

 not well developed on the anterior side of the tooth. On the 

 posterior border there is a well-developed transverse shelf. This 

 tooth is less advanced than P- of Tayassu in that it possesses but 

 a single tubercle on the outer border. 



The other premolar (b, fig. 53) is nearly quadrate in cross- 

 section. The tubercles of the anterior pair are nearly equal. 

 The postero-external tubercle or tritocone is slightly smaller than 

 the protocone. In the postero-internal angle three tubercles are 

 developed. The anterior of these three may represent the 

 tetartocone, the other two belonging to the posterior shelf of the 

 cingulum. This tooth corresponds in development approximately 

 to P 3 of Tayassu. The posterior-internal tubercle is smaller than 

 in that form, but the tooth as a whole comes as near the quadrate 

 form as P 3 of Tayassu. 



Figs. 52 to 53rt. Prosthennops (?) , sp. No. 11876. Thousand Creek 

 Beds, Thousand Creek, Nevada. 



Fig. 52. Inferior canine, X y-<- 



Fig. 53a, P" 2 ?, natural size. Fig. 536, P ; or P 4 , tooth tilted slightly 



toward inner side in the figure, natural size. Fig. 53c, M 3 , natural size. 



Fig. 54. Portion of mandible of a large suilline. No. 19416, X 

 Thousand Creek Beds, Thousand Creek, Nevada. 



Fig. 55. Thinohyus(l), sp. M 3 . No. 11854, natural size. Virgin 

 Valley Beds, Virgin Valley, Nevada. 



54 



55 



