AMERICAN RUMINANT-LIKE MAMMALS. 253 



backbone heavy, and the tail exceedingly long and stout, like 

 that of the great cats. The limb-bones are so peculiar that 

 they cannot be described in a few words ; suffice it to say that 

 they have a great many points of resemblance to those of the 

 carnivorous groups, and the feet are provided with great claws, 

 instead of hoofs, giving them a very sloth-like appearance. 



If it seemed too great a demand upon our imagination to 

 refer Protoceras to the tylopodans, it will appear obviously 

 absurd to call Agriochoerus a camel ; and yet that is the direc- 

 tion in which the evidence, as yet unfortunately incomplete, 

 distinctly points. The Uinta forerunner of Agriochcerus (or 

 what I regard as such) and that of Oreodon have drawn so close 

 together as to indicate the origin of both of these families from 

 some common Bridger ancestor. 



The selenodont fauna of the Uinta, as a whole, is obviously 

 ancestral to that of the White River, with the exception of 

 certain forms, like the anthracotheres, which had immigrated 

 from the Old World in the interval between the two epochs. 

 But we may go farther than this, and may in several instances 

 quite confidently point out the Uinta ancestor of a given 

 White River genus. In other cases there is more uncertainty, 

 because of less complete information, but even in these the 

 Uinta has yielded forms which, if not directly ancestral, are 

 yet very near to the ancestors sought for, and may be taken as 

 representing them for all practical purposes of comparison and 

 study. 



Of these newly discovered Uinta genera one of the most 

 interesting is the genus described by Wortman under the 

 name of Protylopus, which is unmistakably the ancestor of 

 Poebrotherium. It closely resembles the White River genus, 

 but, as we should naturally expect, is smaller in size and more 

 primitive in structure. For example, the dentition is closed 

 and without diastemata ; the premolars are not much extended 

 antero-posteriorly ; and the molars are very short-crowned. The 

 canines, as in the descendant, are small hardly larger than the 

 incisors. The skull, while recalling that of Poebrotherium at 

 the first glance, has a shorter muzzle, a widely open orbit, and a 

 small, hollow tympanic bulla. The neck is, most unfortunately, 



