TRANSACTIONS OF WAGNER 



24 



UINTA SELENODONTS 



crowns of all the premolars are low vertically, extended antero-posteriorly, 

 and provided with sharp edges and acute points. 



The upper molars are of the strictly tetraselenodont pattern, and unworn 

 specimens demonstrate the truth of Wortman's conclusion that the intermedi- 

 ate tubercles were absent. ('98, p. 106.) These molars differ quite markedly 

 from those of the contemporary genus, Protoreodon, not only in the absence of 

 the unpaired cusp (protoconule), which the latter still retains, but also in the 

 form of the external crescents, which in Protylopus are but slightly concave 

 on the outer side and have a very prominent median rib, especially the anterior 

 crescent. The median buttress, which is formed by the junction of the two 

 external crescents, does not contain a prolongation of the median valley. In 

 the oreodont, on the other hand, the outer crescents are much more concave 

 externally and the median rib is less prominent ; the outer median buttress is 

 broader and does contain a narrow prolongation of the median valley. 



The molars of Protylopus increase in size from the first, which is the 

 smallest, to the third, which is the largest of the series, and they are all 

 slightly different from one another in the details of construction. Differences 

 between the molars of various specimens may also be observed. In one case 

 ml has very small anterior and median external buttresses, and the two outer 

 crescents are of similar size and shape, with equally prominent median ribs. 

 In m-^ the buttresses are very much larger, and the rib of the postero-external 

 crescent much less prominent than that of the antero-external one. The 

 buttresses of m-3 are still larger, enclosing small fossettes, and the posterior 

 buttress appears. On m^ and m^ a small pillar occurs between the two inner 

 crescents. In another specimen the anterior buttress on m^- is much larger, 

 while the median buttress is much less prominent in all the molars. 



B. Lozver Jaw. (Plate II., figs. 5, 7.) The incisors are small, especially 

 iy, while i^- and ig- are much larger and of nearly equal size ; they are set 

 en echelon in the jaw. The crowns are chisel-shaped, slightly spatulate, and 

 antero-posteriorly compressed, while those of the upper jaw are laterally com- 

 pressed. The canine succeeds i-g- with hardly any interval; it is not much 

 larger than ig, which it somewhat resembles in shape, but it is more pointed 

 and continues to function as a canine, opposing the upper canine, which it 

 slightly exceeds in size. The premolars follow the canine almost without a 

 break, and are set more closely together than the upper series. Py is almost 

 caniniform ; it is implanted by a single fang and has a compressed, acute, 

 conical crown, without accessory cusps. The other premolars are much more 



