336 LAND MAMMALS IN THE WESTERN HEMISPHERE 



its proportions, the limbs being relatively longer and less heavy 

 and the feet narrower than in the rhinoceroses of the subse- 

 quent geological epochs. The skull, being hornless, had thin, 

 pointed and nearly flat nasal bones, an almost straight and 

 horizontal upper profile, and a short and low, but distinct, 

 sagittal crest ; the cranial bones were quite thin, there being 

 no extensive development of sinuses within them. The artic- 

 ulation of the lower jaw with the skull was only beginning to 

 take on the characteristic peculiarities seen in the later genera, 

 and the hinder margin of the lower jaw was not much thickened. 

 Thus, many of the features which distinguish the skull in all 

 Recent and Pleistocene and most Pliocene, and upper and mid- 

 dle Miocene rhinoceroses were entirely lacking in ^Ccenopus, 

 yet no anatomist could doubt that the White River animal 

 was a genuine rhinoceros. 



The neck was short, but not very heavy, the trunk elongate, 

 but not massive, the ribs not being inordinately long nor 

 strongly arched, and the hip-bones so little expanded that 

 they were tapiroid rather than rhinocerotic in appearance. 

 The limb-bones were relatively much more slender than in any 

 existing species, and, although every one of them was char- 

 acteristically that of a rhinoceros, yet the comparative light- 

 ness of body and slenderness of limb gave to these bones a cer- 

 tain resemblance to those of tapirs. The feet, which were 

 moderately elongate and rather narrow, were three-toed, as in 

 all subsequent North American species and in all existing 

 members of the family. 



The most ancient and primitive representative of the true 

 rhinoceroses so far discovered occurs in the lowest division of 

 the White River beds and is of particular interest as throwing 

 light upon the origin of the family. The genus {^Trigonias) 

 differed from that {^Cmnopus) which was so abundant in the 

 middle White River substage in several highly significant 

 particulars, though on a merely casual inspection one might 

 easily be misled into thinking that the two animals were nearly 



