TRANSACTIONS OF WAGNER 



UINTA SELENODONTS 



the large, convex facet for the pyramidal, while the lunar facet is relatively 

 smaller and more oblique than in the White River genus. A large facet 

 receives the projection of the third metacarpal ; it is relatively larger than in 

 Poebrotherium and vertical, not inclined downward and outward as in the 

 latter. Another difference is seen in the proportions of the distal facets, that 

 for the fourth metacarpal being relatively smaller, and that for the fifth much 

 larger than in the White River type. 



One of the features which most clearly distinguish Protylopus from 

 Poebrotherium is the character of the metacarpus. In the latter it is reduced 

 to two functional digits (iii., iv.) and two small nodules representing the 

 proximal ends of ii. and v. In the Uinta genus, on the other hand, there are 

 four functional digits, though the median pair are considerably enlarged and 

 the lateral pair much reduced. Wortman's conjecture as to the composition 

 of the manus is thus demonstrated to be correct. 



In the only manus which the collection contains (No. 11,222) the distal 

 ends of all the metacarpals are missing, so that their length can be ascer- 

 tained only approximately ; it is clear, however, that these bones are much 

 shorter than in Poebrotherium, in proportion both to the length of the metatar- 

 sus and to that of the other limb-bones. 



The first metacarpal may have been present, but if so, it must have been 

 in a rudimentary condition, and no trace of it is preserved in the specimen. 



Metacarpal ii., though apparently not much shorter than mc. iii., is very 

 slender, but is far more robust than the corresponding metatarsal. The prox- 

 imal end is narrow but quite thick in the dorso-palmar dimension, and bears a 

 narrow, plain facet for the trapezoid, but appears not to come into contact 

 with the magnum. The shaft is straight, very slender, and laterally com- 

 pressed; its proximal half is closely applied to mc. iii. and is thus flattened on 

 the ulnar side, having a trihedral section; below this it becomes more rounded. 

 At the distal end the shaft is slightly expanded and is probably a little wider 

 than the trochlea. 



Metacarpal iii. is longer, much heavier, and in every way differently shaped 

 from mc. ii. ; the proximal end is but little broader than the shaft and its 

 increased width is principally due to the unciform process. The magnum 

 facet is quite strongly concave transversely, much more so than in Poebrothe- 

 rium, in which this facet is nearly plane. The head of mc. iii. rises consider- 

 ably above that of mc. iv., and sends a process which, though not long and not 

 extending much across mc. iv., has yet a large contact with the unciform, rel- 



