FREE INSTITUTE OF SCIENCE 



75 



UINTA SELENODONTS 



The manus (Plate III., fig. 17) bears a close general resemblance to that 

 of Leptomeryx both in size and appearance, save that the lateral digits are 

 much less reduced. The carpus is broad and rather low, although the distal 

 elements are not so much shortened as they are in the White River genus. 

 The scaphoid is of only moderate size, low, broad, but rather thin in the dorso- 

 palmar dimension, and, except that it is somewhat thinner, it resembles that 

 of Protylopus. The distal end is divided somewhat unequally between the 

 facets for the trapezoid and magnum, the former rather the larger of the two. 

 Although the trapezium was probably present, no distinct facet for it is visible 

 upon the scaphoid. 



The lunar is quite high and narrow, though less so than in Leptomeryx ; 

 the proximal end is not so much expanded transversely as in the latter, not 

 sending out such a prolongation towards the pyramidal ; the distal end is a 

 wedge-shaped beak, formed by the junction of the magnum and unciform 

 facets, which meet at nearly a right angle, and of which the former is slightly 

 the larger. This symmetry of articulation between the lunar and the distal 

 bones of the carpus is somewhat exceptional in this group. In Protylopus 

 the unciform facet is larger than that for the magnum, while in Leptomeryx 

 the lunar rests almost entirely upon the unciform and has only a lateral con- 

 tact with the magnum, as is also true of all the oreodonts, even of Protoreodon. 

 In Protoceras, however, there is only a slight tendency towards this displace- 

 ment and the two facets are not far from equal in size, though that for the 

 unciform is a little larger and more distal. 



The pyramidal is a relatively large bone, slightly exceeding the scaph- 

 oid in all its dimensions except in breadth. On its palmar side is developed a 

 large and prominent rugosity, such as is but feebly indicated upon the scaph- 

 oid. Of course, the large size of the pyramidal is to be correlated with the 

 stoutness of the ulna, and forms a decided contrast to the reduced pyramidal 

 of Leptomeryx. The ulnar facet is a transverse groove, with dorsal border 

 much elevated at the radial side, but descending steeply towards the ulnar 

 side ; the pisiform facet is small and separated by a distinct ridge from the 

 ulnar surface, with which it forms nearly a right angle. Articulation with 

 the lunar, so far as the dorsal side is concerned, is by means of two facets, 

 proximal and distal, with a sulcus between them. A simply concave facet for 

 the unciform occupies the entire distal end. 



The pisiform is smaller than in Protylopus or Leptoreodon and of a differ- 

 ent shape; its proximal end is transversely extended, which is unusual among 



