34: 



E. L. Troxell — Horned Eocene Ungulates. 



The first incisor is absent, otherwise every tooth of the 

 superior series is represented. The lower jaws are not 

 present. 



In two important respects this specimen is different 

 from any Hyrachyus. It has the double internal cone 

 on the third and fourth premolars, and has incipient 

 horn rugosities on the nasals. 



10258 TYPE 



Y. P. M. 



Fig. 4. — Metahyracliyus bicornutus, gen. et sp. nov. Top view of skull 

 showing what appears to be the beginning of the horn supports in the great 

 family of the rhinoceroses. X%- 



The first feature, the separation of the tetartocone 

 from the deuterocone, at once reminds us of many 

 species of the later rhinoceroses, in which there is a 

 tendency for the premolars to become molariform. 

 Because the metaloph is so abbreviated, we find its 

 nearest comparison with Ccenopus (see C. platycephalus 

 (Osborn and Wortman) ). 



The second important feature, the appearance of horn 

 rugosities on the ^asals of this species, is a matter of 

 great significance; for some such race must have given 

 rise to Diceratherium armatum Marsh and to Menoceras 

 coohi (Peterson) in the later Oligocene and Miocene 

 periods, in which we see the same transverse arrange- 

 ment of the two elements. This may mark the beginning 



