THE MAMMALIA OF THE DEEP RIVER BEDS. 139 



der to enter the groove on the radius already mentioned. The ulnar side of the 

 scaphoid is concave and is chiefly occupied by the large inferior facet for the lunar. 

 The distal side is taken up by two facets, those for the magnum and trapezoid respec- 

 tively. The magnum facet is the larger of the two and is deeply excavated behind, 

 but descends abruptly in front. The lunar is both high and broad; its radial surface 

 is saddle-shaped, concave from side to side and convex fore and aft, broad in front, 

 much contracted and tapering behind. The radial side carries two facets for the 

 scaphoid, the upper one small and nearly plane, the lower very large and convex and 

 separated from the magnum surface by a scarcely perceptible ridge. The latter facet 

 is almost entirely lateral, except on the palmar border, where it is reflected under- 

 neath so as to be partly distal. The unciform facet is concave and obliquely placed ; 

 it forms with the magnum surface a sharp beak, which is wedged in between the 

 magnum and the unciform and extends nearly to the third metacarpal. 



The cuneiform is broad and low and has a less dorso-palmar diameter than the 

 other proximal carpals. The ulnar surface is a narrow groove which is reflected 

 down upon the external side of the bone, and the pisiform facet forms a broad band 

 upon the palmar side which is continuous with the ulnar facet. Distally, the cunei- 

 form displays a simply concave facet for the unciform. The pisiform is intermediate 

 in character between the condition found in the earlier and that in the later genera of 

 the family, being more expanded at the free end than in the former, less so than in 

 the latter. The proximal end is much contracted and bears a single rounded articular 

 surface, part of which is for the ulna and part for the cuneiform. 



The trapezium is a small nodular bone which has but two facets, one for the 

 trapezoid and, at an obtuse angle with this, another for the second metacarpal. This 

 species and Merycoclicerus montanus are the only members of the family in which I 

 have succeeded in obtaining the trapezium, though the facets on the neighboring 

 bones leave no room for doubt as to its presence in the other genera as well. This 

 carpal enables us to state with entire confidence that in Mesoreodon the pollex is not 

 represented even by a rudiment. The trapezoid is a large bone both vertically and 

 transversely, but it has no great antero-posterior depth ; proximally, it bears a large 

 and simply convex facet for the scaphoid and its radial side is occupied by a concave 

 surface for the trapezium. Distally, there are two facets, one of which is laro-e and 

 slightly concave, the other small, plane and inclined at an open angle to the first- the 

 former is the surface for the second metacarpal and the latter for the third. 



The magnum is a very characteristic bone, resembling strongly that of Mery- 

 cliyus and Merycochcerus, though its peculiarities are not carried to such an extreme. 

 Seen from the front, the magnum appears to be smaller than the trapezoid, and is 



