THE MAMMALIA OF THE UINTA FOKMATIOX. 519 



In tlie line of genefa to which it belongs the cliaractors of the premolars in 

 respect to the gradual assumption of the niolai' pattern are vei y important. These 

 are wanting in the Uinta specimens, but the Bridger species, which was formerly 

 referred by us* to Helaletes (IT. latidens) is closely related to Isectolophus, if not gen- 

 erically the same, and shows double internal lobes upon both pm. ' and pm. \ The 

 second upper premolar probably had two external lobes and one internal lobe. The 

 distinctive features of the dentition, so far as known, are seen in the conic postero- 

 external lobe of the upper molars, in the third lobe of the last lower molar and the 

 absence of a diastema in the lower jaw. As pointed out in our preliminary descrip- 

 tion, these features place Isectolophus in or near the true tapir line. This conclusion 

 is sustained by the discovery of the complete carpus and of the cuboid. The carpus 

 is of a more primitive type than that of Triplopus, since the magnum and cuneiform 

 surfaces of the lunar are subequal, as in Ili/rachi/us, while in Triplopus the magnum 

 sui-face is much reduced, leading to the Hyracodon type. A still more important 

 feature is the size of mc. v, as shown by its articular facet upon the cuneiform, in- 

 dicating that there were four functional toes. The cuboid, when compai-ed Avith that 

 of Triplopus, is broad and reduced in vertical diameter. 



Generic characters. Dentition, c. 1, p. I, m. s. No diastema behind the 

 canine. Fourth and probably thiid premolai's in both jaws submolariform or with 

 double internal lobes. Molars in both jaws resembling those of Tapirus. External 

 lobes of superior molars (paracone and metacone) strongly convex and equal in size. 

 Last lower molar with prominent third lobe. Manns and pes. Digits, 4-? 3. 

 Lunar with subequal magnum and unciform facets. Cuboid broad with an extensive 

 astragalar facet. 



Isectolophus amiectenSjf nobis. The postero-external lobes of the superior molars 

 are produced beyond the junction of the j^osterior transver.sc crests. A strong cing- 

 ulum surrounds the crown. 



/. (Ileldletes) lalidens,* nobis. The postero-external lobes are opposite the junc- 

 tion of the ])ostenor crests. There is no cingulum. 



The Biidger species may subsequently be loiiinl to represent another genus, but 

 in the absence of the complete dentition of Isectolophus, it can only be separated l)y 

 the characters of the molar crests, which are hardly generic. The structure of the 

 premolars removes this genus from Systemodon Cope. 



• K. M. Museum Bullelin, No. 1, tS7.S, p. 54. 

 + Proc. Am. Phil. Soc. Sept. 2. 1987. p. 260. 

 } E. M. Jliiseuni Hull-lin. No. I, 1878, p. 54. 



