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UINTA SELENODONTS 



median prolongations of the frontals ; the narrowness of these bones is due 

 both to the slenderness of the cranium and to the large size of the squa- 

 mosals. 



The squamosal is a very large bone, both longitudinally and vertically, 

 and makes up the greater part of the cranial side-wall ; it is highest behind, 

 its suture with the parietal running quite steeply downward and forward. 

 The posttympanic process is short, but quite thick, and is made conspicuous 

 by its separation from the paroccipital ; the notch between the posttympanic 

 and postglenoid processes is narrower than in Leptomcryx or Protylopus. The 

 root of the zygomatic process forms a much narrower and more horizontally 

 directed shelf than in the White River genus, and the glenoid cavity is of 

 quite a different form. In Leptomeryx the articular surface is larger and nearly 

 flat or slightly convex; from the external side it is invaded by a large, deep 

 concavity, which is visible as a broad sulcus when the skull is seen in lateral 

 view, and which intervenes between the articular surface and the postglenoid 

 process ; internally the two are continuous. In Camelomeryx the surface is 

 broad and simply convex, and only a slight indication of the external sulcus 

 is visible ; the postglenoid process is high, broad and thick, even larger than 

 in Protylopus, and much larger than in Leptomeryx. The zygomatic process is 

 broken away, but the form of the jugal shows it to have been longer than in 

 the last-named genus. 



The jugal is long, quite heavy in front, especially in the vertical dimen- 

 sion, and tapering posteriorly ; it is largely expanded upon the face, both in 

 front of and beneath the orbit ; the masseteric surface is broad and distinct 

 and is bounded by a prominent masseteric ridge ; the postorbital process is 

 exceedingly small and is widely separated from that of the frontal. This jugal 

 differs in several important respects from that of Leptomeryx; it is longer, 

 shallower vertically, but thicker and less plate-like; the masseteric surface 

 and ridge are much better developed and the postorbital process much 

 smaller, leaving the orbit far more widely open behind; the inferior boun- 

 dary is flat and not flared out into a prominent lip, as it is in the White 

 River genus. As a whole, the zygomatic arch is longer than in the latter, 

 both because the glenoid cavity is farther behind the molar series and because 

 the orbit does not extend so far back. In both genera the anterior boundary 

 of the orbit occupies the same position, above m- 1 -, but in Leptomeryx the 

 orbit is larger and its hinder margin is well behind the molars, while in the 

 Uinta genus it extends only to the posterior edge of m 5 . 



