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

 Ccenopus platycephalus nanolophus, subsp. nov. 



(Fig. 3.) 

 Holotype, Cat. No. 12489, Y. P. M. Middle or Upper Oligocene, Colorado. 



This new subspecies is founded on a liolotype consist- 

 ing of the permanent upper molars and premolars of a 

 young individual. The new name has reference to the 

 dwarfed condition of the metaloph. It represents an 

 unde scribed species of rhinoceros near C. platycephalus 

 but because of its incompleteness is ranked as a sub- 

 species. 



The tetartocone in each premolar except P^ is closely 

 joined to the deuterocone, and in P^ these constitute a 

 single element. P^ varies from the others in having a 

 groove on the outer side defining the two cones, which in 

 this case are united to form a continuous loop of the inner 

 lophs. On P^ the metaloph is large and curves backward 

 to enclose the postfossette; the protoloph is short and 

 straight, while the ectoloph is broad and heavy and 

 occupies the greater part of the tooth. 



Fig. 3, — Cceiiopus platycepJialus nanolopJiiis, subsp. nov. Holotype. 

 Molar-premolar series. X 1/3- 



In most species of CcBnopus the anterior side of the 

 larger premolars is greatly lengthened by having a prom- 

 inent protocone antero-exteriorly, and a tritocone so sub- 

 dued that this part of the ectoloph is smooth exteriorly, 

 as in the molars. In the specimen under discussion, 

 however, the equal prominence of the two outer cones 

 gives this side of the tooth a squared form ; the ectoloph 

 is at right angles to the anterior and posterior sides of ^ 

 the tooth. The premolars (except P^) are thus subquad- 

 rate, with the inner sides rounded. The parastyle and 

 metastyle are separated by grooves from the prominent 

 exterior cones. 



The anterior cingulum is strong on each tooth except P^ 

 but it does not encircle the inner border completely. On 



