TRANSACTIONS OF WAGNER 

 96 



UINTA SELENODONTS 



already assumed their characteristic shape, the lower canine going over to the 

 incisors and the first lower premolar becoming caniniform. The upper molars 

 retain the fifth cusp (protoconule) in the anterior half of the crown, but their 

 form is already characteristically oreodont ; the lower molars are less advanced 

 and resemble those of Agriocliacrus in the conical inner cusps and the widely 

 open valleys. The premolars are typically oreodont but somewhat simpler in 

 construction than those of the White River representatives of the family. 



The skull is oreodont but has a longer and less capacious cranium than in 

 the later genera of the group, with orbits widely open behind and no lachry- 

 mal pit; the mandible is likewise oreodont in shape, but has a longer and more 

 recurved coronoid process and angle more extended behind the condyle. The 

 vertebral column differs but slightly from that of the White River genus, the 

 principal difference being in the more peg-shaped character of the odontoid 

 process of the axis and in the longer and more massive tail. The entire 

 character of the limbs is oreodont ; scapula, humerus, ulna and radius, pelvis, 

 femur, tibia, and fibula differ in no important way from those of Oreodon itself, 

 only the manus and pes are distinctly more primitive than in the latter. In 

 the manus the displacement of the lunar over upon the unciform is already 

 indicated, but is much less extreme than it afterwards became, and the pollex 

 is somewhat less reduced. In the pes a remnant of the first metatarsal is still 

 [fide Marsh) attached to the ento-cuneiform. The phalanges are rather more 

 slender and the unguals more pointed than in Oreodon. 



While there is little room left for doubt that Protoreodon is thus the 

 ancestral form whence were derived Oreodon and its successors, Eporeodon, 

 Jl/esoreodon, Merycochccrus, Merychyus, the Uinta material gives us no help in 

 determining the genealogy of those curious aquatic oreodonts, Lcptaitchenia 

 and its successors. This genus suddenly makes its appearance in the upper 

 White River (Protoceras beds), and nothing has yet been found in the Oreo- 

 don or Titanotherium beds which can be regarded as ancestral to it, or which 

 will explain its exact relationship to the more typical members of the family. 

 Whether this line had already begun its separate existence in Uinta times, or 

 whether it first branched off from the main stem in the older White River, 

 must be left for future discovery to determine. 



A larger and more important question is that concerning the relationship 

 of the oreodonts as a whole to the other artiodactyl groups. Upon this sub- 

 ject the most diverse possible opinions have been expressed by the various 

 students of the problem. Leidy was the first to call attention to the manifold 



