Peterson: Material Discovered in Uinta Basin. 135 



In the type, No. 3007a, there are three lower incisors, which are 

 procumbent in position, of subequal size, with laterally expanded or 

 fan-shaped crowns (PI. XXXVI, Fig. i). The canine is placed close 

 to l-r^ and is but very little larger than the incisors in the type, wliile in 

 an adult specimen No. 2990^-^ it is slightly larger in proportion. On 

 the whole the tooth in this species is relatively larger than in the 

 Oligocene genus Ilyracodon and it is also more oval in cross-section. 

 In the type there are four upper and lower milk-teeth, while in the 

 adult specimen. No. 2990, Py is absent.^'" In the Uinta genus there 

 is not developed the strong rib near the median portion of the ectoloph 

 on the lower molars and premolars, nor is the heavy cingulum seen in 

 Ilyracodon present. There is in the type specimen a decided swelling 

 on the posterior face of the protoloph, represerlting the antecrochet, 

 and the prefossette is well indicated, but the crista is little or not at 

 all represented, while in Hyracodon the crista is much better developed 

 and the antecrochet is prominent. M- is just appearing through the 

 alveolar border. This young tooth has the posterior face of the ecto- 

 loph perfectly smooth, there being no spur of the ectoloph represented 

 as in Triplopus cuhitalis or Prothyracodon obliqiddens. This feature 

 was thought to be due to the immaturity of this tooth in the Carnegie 

 Museum specimen, but it is perhaps more probable that the present 

 well calcified crown would not before its final eruption add the char- 

 acteristic spur seen in Hyracodon of the Oligocene or in the contem- 

 porary species of the Uinta deposits. Too much stress, however, 

 should not be laid upon this highly interesting Rhinocerotic feature of 

 M- in the specimen at hand, until the discovery of fully adult upper 

 dentitions. If this character is found in M- of fully adult specimens, 

 P. uintense should be placed in a distinct genus. 



The base of the skull appears to be proportionally broader than in 

 Hyracodon, which may be due to crushing. Whether or not there is a 

 tympanic bulla cannot be determined. Unfortunately the important 

 region of the external ear is also too much mutilated to determine 

 whether it is like that in Hyracodon or whether it is closed inferiorly 

 as in Triplopus cuhitalis. There is a long and well defined sagittal 

 crest and the supra-orbital ridges are also indicated in this young 

 individual. 



'2° No. 2990 is provisionally referred to P. uinlense on account of its large size, 

 which is taken as an indication that it pertains to the same species. 



12" The first premolar above and below are very rudimentary, and their absence 

 or presence in this genus is perhaps not of great phyletic importance. 



