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 UINTA SELENODONTS 



266, fig. 18.) P— is composed, as usual, of two transversely placed crescents, 

 of which the outer one is more concave externally than in the other pre- 

 molars ; in P. paradoxicits the inner crescent is more conical and has less 

 clearly marked horns than in the other species. 



The upper premolars of Oreodon are just such as might be expected in 

 the direct successor of the Uinta genus. Leidy says of the anterior three : 

 " Their crown is a trilateral pyramid, with a pointed apex and a broad external 

 cordiform surface. The narrower internal surfaces appear as triangular in- 

 clined planes, separated by a median acute ridge extending from the point to 

 the base of the crown. The anterior of the internal surfaces forms at the 

 base a pair of shallow pouches, defined by a double festoon. The posterior of 

 the same surfaces forms a single and larger pouch at the base of the crown, 

 included by a single and thicker festoon. This latter in the third premolar 

 almost assumes the dignity of an additional lobe to the crown, resembling the 

 internal lobes of the true molars." ('69, p. 81.) 



The upper molars of Protoreodon are primitive in a very interesting way, — 

 viz., in the retention of the anterior intermediate cusp (protoconule), though 

 in other respects these teeth are already well advanced in the assumption of 

 the selenodont character. They are extremely brachyodont, and are broad in 

 proportion to their antero-posterior length. In size they increase from the 

 first to the third. The external crescents are more concave on their outer 

 faces than in Oreodon, and the median ribs upon those faces are far more 

 prominent, as are also the external buttresses, all of which constitutes a marked 

 resemblance to the molars of Protylopus and the Leptomerycidtz. The inner 

 crescents, especially the anterior one, have less extended horns than in Oreo- 

 don, and the median valley is thus more widely open. The unpaired cusp is 

 very small and in worn teeth soon becomes unrecognizable; such molars con- 

 siderably resemble those of Leptoreodon and Camelomeryx in a corresponding 

 stage of wear. The cingulum is much better developed than in Oreodon, and 

 is almost continuous upon the front, internal, and hinder faces of the teeth. 



The molars of Oreodon are so very familiar that they require no descrip- 

 tion. Suffice it to say that a comparison with those of the Uinta genus is 

 extremely suggestive of a direct genetic connection between the two. 



B. Lower Jaw. The incisors have simple, chisel-like crowns, and the 

 canine has become one of them in form and function ; these teeth are much 

 more erect than in Protylopns or the Leptomerycidce. The premolars are dis- 

 tinctively of the oreodont type, but they are simpler and much more com- 



