408 LAND MAMMALS IN THE WESTERN HEMISPHERE 



tions and appearance, these dainty little creatures must have 

 been very like the existing chevrotains or " mouse-deer " of 

 Asia and the Malay islands, and by many writers they have 

 been classed in the same suborder, the Tragulina. The upper 

 incisors had been suppressed and the upper canine reduced to 

 very small size, while the lower canine had become functionally 

 one of the incisors. The skull had a very long and slender facial 

 region, but had a less llama-like appearance than in ]Hypertra- 

 gulus. The neck was short and the fore limbs much shorter than 

 the hind, so that the back sloped downward from the rump to 

 the shoulders, as in the chevrotains. There was a remarkable, 

 indeed quite unparalleled, difference between the fore and hind 

 limbs and feet, the hinder extremity being not only much longer, 

 but also much more specialized, while the anterior one retained 

 in very large degree its primitive characteristics. Thus, in the 

 fore-arm the ulna was complete and separate from the radius, 

 but in the lower leg the fibula was reduced to its minimum. In 

 the manus there were four entire and functional digits, in the 

 pes only two, which were joined in a cannon-bone. 



Finally, there was a fourth phylum, that of '\Hypisodus, which 

 was confined to the White River stage and is still incompletely 

 known. This was a tiny creature, much smaller than any of 

 the preceding ones, and is the only known White River un- 

 gulate with fully hypsodont grinding teeth. Another very ex- 

 ceptional peculiarity of its dentition was that in the lower j aw 

 it had ten incisor-like teeth ; not only the canine, but the first 

 premolar as well, had assumed the character of the incisors. 

 This same peculiarity is found in the lower Miocene fgazelle- 

 camel, \Stenomylus (see p. 394), but in no other mammal. 



A considerable assemblage of genera belonging to this family 

 occurs in the upper Eocene, but the material yet obtained is too 

 fragmentary to permit the assignment of these forms to the 

 different phyla, though it is very probable that among them are 

 to be found ancestors of all the White River and subsequent 

 genera. 



