FREE INSTITUTE OF SCIENCE 

 UINTA SELENODONTS 



of any of these genera in which the unpaired cusp has been suppressed. In 

 size the molars increase successively from ml to m- 3 ; they are considerably 

 wider transversely than long antero-posteriorly, and are of nearly regular 

 quadrate outline, though the front half of the crown is slightly broader than 

 the hinder half. The first molar is small, its external crescents have more con- 

 cave outer faces than in Protylopus, and the external buttresses are but little 

 larger. On the second and third molars the antero-external buttress has 

 become very large, much more so than in Protylopus, but the outer crescents 

 are more concave than in that genus, and the median rib of the anterior one 

 is rather less prominent. 



B. Lower Jaw. (Plate II., figs. 10, 12.) The incisors are quite procumbent, 

 and in length diminish slightly from i T to i-g-, while in breadth the relation is 

 reversed, i-g- being slightly broader than i T ; the crowns are simple and chisel- 

 shaped, broadest at the cutting edge and tapering to the root. The canine 

 resembles a fourth incisor, and follows upon the third after an interval no 

 greater than that between i^- and i-g- ; the crown is a little shorter and wider 

 than that of the latter. 



The premolars are rather complex for an Uinta artiodactyl and are of 

 highly characteristic form. The first is isolated by a short diastema in front 

 of and a much longer one behind it; it is a large caniniform tooth, implanted 

 by a single fang, and stands much higher than any other of the mandibular 

 teeth; the crown is simple and quite thick, and is worn obliquely on the 

 anterior face by the attrition of the upper canine, which it opposes. In shape 

 and function this tooth is like the caniniform premolar of the oreodonts ; but 

 this peculiar transformation is not confined to the latter family; it is repeated 

 in the males of Protoceras, and in Leptomeryx p T , although very small and 

 almost rudimentary, is in form a canine, and irresistibly suggests that it must 

 once have functioned in that capacity. 



The second premolar is short antero-posteriorly and is carried upon two 

 fangs ; the crown is perfectly simple, high, compressed, trenchant, and acutely 

 pointed. The third premolar resembles p^-, except that it is more extended 

 antero-posteriorly and has on the inner side of the crown a short, compressed, 

 plate-like ridge, which runs a short distance back from the central apex and 

 partially encloses a fossa, that is, however, open behind, very much as in p T of 

 Leptotragulus. The fourth premolar has a large, conical, internal cusp (deutero- 

 conid) in place of the inner ridge, a feature which clearly demarcates this 

 genus from Leptotragulus. 



