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UINTA SELENODONTS 



toid, and the other cervicals are of normal structure. The limbs are much 

 like those of Leptomeryx and Poebroiherium ; the ulna and radius are coossi- 

 fied, the trapezoid and magnum separate, and the manus tetradactyl. The 

 fibula is completely reduced, the cuboid and navicular distinct, and the pes 

 didactyl, but without a cannon-bone. 



13. Protoceras is clearly related to Leptomeryx, and if the latter is referred 

 to the Tylopoda, the former must likewise be so classified. 



14. Protylopus (Uinta) has an undiminished dentition without diastemata, 

 but with the canines of very small size. The teeth are extremely like those 

 of Poebrotherium, but less elongate and more brachyodont. The skull is also 

 extremely like that of Poebrotherium, but has a less elongate muzzle, less 

 capacious cranium, and a small tympanic bulla, free from cancelli ; the coro- 

 noid process of the mandible is more ruminant-like. The thoracic, lumbar, 

 sacral, and caudal vetebras resemble those of Poebrotherium, as does the fore- 

 limb, the ulna and radius showing incipient coalescence in old individuals ; 

 the manus is, however, tetradactyl. Pelvis, femur, and tibia are entirely tylopo- 

 dan ; the fibula is uninterrupted but with extremely slender shaft. In the pes 

 the lateral metatarsals are elongate, filiform splints. 



15. Protylopus seems almost certainly to be the direct ancestor of Poe- 

 brotherium, and thus the most ancient known member of the Camclidm. 



16. A closed dentition does not necessarily imply that the animal is 

 capable of no further development. 



17. The very small canines in Protylopus and Poebrotherium, and their 

 gradual enlargement in Gomphotherutm and the subsequent genera of the 

 phylum, indicate that structures may first be reduced and then enlarged in a 

 phyletic series, while the elongation of the premolars in Poebrotherium and 

 their reduction in the later genera show that structures may first be enlarged 

 and then reduced. 



18. Leptotragulus (Uinta) is very imperfectly known; its mandibular 

 dentition is very much like that of Poebrotherium, but appears to differ from it 

 in the suppressionof p T and the large size of the canine. 



19. Leptotragulus may, when better known, prove to be the ancestor of 

 Hypertragjilus. 



20. Leptoreodon (Uinta) has an unreduced dentition, with small, conical 

 upper incisors, a stout D-shaped upper canine, and diastemata between p. I and 

 p. 2. The lower canine has become incisiform and p T caniniform, as in the oreo- 

 donts ; the upper premolars are simple and the molars composed of four cres- 



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