E. L. Troxell — Ccenopus, the Ancestral Rhinoceros. 47 



P^ the postero-interior cingulum rises high on the tetar- 

 tocone, and forms a veritable cusp or cone ; it descends 

 sharply on the inner side and becomes broken along the 

 base of the deuterocone. On P^ it becomes an integral 

 part of the tetartocone, and on P^, antero-interiorly, the 

 cingulum blends with the deuterocone, rising high on the 

 side to do so. The posterior cingulum of each molar is 

 much less extended than is usual in the rhinoceroses of 

 this time, so that not only is the hypocone a smooth 

 rounded base, but the median valley also is uninterrupted 

 by cusp or cingulum, in this respect differing from C. 

 platycephalus. The postfossette is very small on M^-^ 

 and on M^ is entirely lacking. The antecrochet on the 

 molars is low and broad, while an inconspicuous crista 

 is present on each of the larger premolars. 



An unusual feature is seen on these premolars, in that 

 the postfossette is larger than the medifossette and the 

 two are confluent, due to the short metaloph ; the median 

 valley opens backward instead of inward and this, 

 together with the dominance of the deuterocone, consti- 

 tutes the chief feature of the subspecies. The type of the 

 subspecies is about ^ve sixths the size of that of C. 

 platycephalus. 



Ccenopus tridactylus metalophus^ subsp. nov. 



(Fig. 4.) 



Holotype, Cat. No. 10254, Y. P. M. Probably Middle Oligocene, Eush- 

 ville, Nebraska. 



The holotype of this new subspecies shows a strong 

 tendency to have the cross lophs of all the premolars par- 

 allel and unconnected. The form of these lophs would 



Fig, 4. — Ccenopus tridactylus metalophus, subsp. nov. Holotype. Molar- 

 premolar series. X 1/3- 



seem to link it with C. tridactylus (Osborn) and remotely 

 with Diceratherium Marsh. There is evident a close sim- 



