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69 



UINTA SELENODONTS 



almost completely obliterated. The second is also much abraded, making an 

 exact comparison with Leptoreodon difficult, but it is obvious that the external 

 median buttress is distinctly larger than in the latter. The third molar may 

 be fully compared with that of the allied genus, which it resembles closely, 

 but differs in the larger size of the external buttresses, especially of the 

 median and posterior ones, which are very small in Leptoreodon ; the ribs 

 upon the outer crescents are also more prominent than in the latter. It is 

 interesting to observe that these differences are in the direction of Lepto- 

 meryx. From Protylopiis the two allied genera differ in the greater breadth 

 of the upper molars. 



The skull (Plate III., fig. 15) in its general character closely resembles 

 that of Leptoreodon and less nearly that of Protylopus, but has some well- 

 defined peculiarities of its own. It has the characteristic tylopodan form 

 which recurs so often among these Uinta genera and which is so well shown 

 in Protylopus, Leptoreodon, Leptonieryx, Hypertragidus, and even in Protoceras. 

 The cranium, measured from the occipital condyles to the anterior border of 

 the orbit, is considerably longer than the facial region, though the brain-case 

 proper is rather short and quite slender. Its narrowness and the great depth 

 of the postorbital constriction are in decided contrast to the conditions found 

 in Leptoreodon and Protylopus, in which the brain-case is broader and the 

 postorbital notches shallower. In similar contrast to the twO genera men- 

 tioned is the sagittal crest, which is high and prominent, and which occupies 

 the entire length of the parietals, the temporal ridges being short and con- 

 fined to the frontals, where they pursue a nearly transverse course, instead of 

 converging gradually into the sagittal crest, as they do in Leptoreodon and 

 Protylopus. The forehead is broad over the orbits, ceasing abruptly behind, 

 but contracting gradually in front into the narrow, rounded muzzle. The 

 orbit is quite small and has an anterior position, its front margin lying above 

 the middle of ml, almost the same position that it occupies in Leptonieryx. 



In Leptoreodon the orbit is larger and not so far forward, and in Protylopus 

 also it has shifted backward, in consequence of which the muzzle is as long as 

 in Camelomeryx, despite the fact that Protylopus is without diastemata. 



The occiput is small and low, broad at the base, but contracting rapidly 

 towards the summit ; its shape is as in Leptonieryx, but it is actually and 

 relatively lower and narrower. The basioccipital is quite elongate and very 

 broad proportionately; its ventral surface is nearly flat, but is broken near 

 the anterior end by two low eminences, between which is a broad, shal- 



