252 BIOLOGICAL LECTURES. 



long-lived and diversified group of the Oreodontidae. The type 

 genus is Oreodon, by far the commonest of White River fossils, 

 at which time great herds of O. culbertsoni roamed over the 

 western plains. In this genus the dentition is closed, without 

 diastemata ; the upper canine is large, but the lower is incisi- 

 form, its place being taken by the caniniform first premolar. 

 The other premolars are simple and trenchant, and the molars 

 very like those of the deer. The skull has a rather short face 

 and very long, narrow cranium ; the orbits are completely encir- 

 cled with bone, and a deep pit impresses the surface of the 

 lachrymal. The neck is short, the trunk long, and the tail 

 very long and heavy. The limbs and feet are short and thick ; 

 a rudimentary pollex is retained in the forefoot (this is the first 

 artiodactyl in which that structure was demonstrated) ; and the 

 hoofs are curiously rounded and flattened. In appearance and 

 general proportions the skeleton of this genus recalls that of 

 the modern peccary. 



The taxonomic position of the oreodonts has been the subject 

 of a great deal of discussion, and almost every possible opinion 

 has been expressed ; but the evidence of the Uinta fauna is 

 very strongly in favor of the view held by Riitimeyer and 

 Schlosser; namely, that they are aberrant members of the 

 Tylopoda. In time they ranged from the Uinta through the 

 Loup Fork, each successive horizon yielding peculiar genera ; 

 but with their later modifications we need not concern our- 

 selves. Geographically they were entirely restricted to North 

 America. 



The most extraordinary and puzzling of White River mam- 

 mals, not even excepting Protoceras, is Agriochcerus . Before 

 complete skeletons of this creature had been collected, the 

 skull and feet had been found separately, and were referred to 

 no less than three distinct and widely separated mammalian 

 orders. The dentition resembles that of Oreodon in the char- 

 acter of the canines, but the molars are much less distinctly 

 selenodont and have a decided resemblance to those of the 

 European genus Ancodus. The skull is oreodont except in a 

 few details, such as the absence of the lachrymal pit, the 

 incomplete closure of the orbit, etc. The neck is short, the 



