THE MAMMALIA OF THE DEEP RIVER BEDS. 141 



type. In the second species of Mesoreodon, M. intermedins, to be described hereafter, 

 the proportions of the metacarpals are more like those of Merychyus. 



The second metacarpal is short and slender, with a trihedral recurved shaft ; the 

 head is rather broad and bears a triangular, nearly plane facet for the trapezoid and 

 a postero-internal one for the trapezium. This bone does not reach the magnnm, 

 which constitutes an important difference from the manns of JSporeodon, in which, as 

 in the more ancient genera, mc. ii is in contact with the magnum. The third meta- 

 carpal is likewise different from that of the last-named genus ; the head is expanded 

 and deeply concave transversely and convex antero-posteriorly ; on the radial side is 

 a very small oblique facet for the trapezoid and on the ulnar side a very large one for 

 the unciform. Both of these surfaces are confined to the anterior half of the meta- 

 carpal. Beneath the unciform projection on fhe head of mc. iii the bone is excavated 

 to receive the head of mc. iv ; posterior to this, and separated from it by a deep sulcus, 

 is a second facet placed on a projection, which extends towards the ulnar side. This 

 facet is somewhat oblique and extends beneath the head of mc. iv and the two bones 

 are thus interlocked in a very complex and perfect manner. The same arrangement 

 is indicated in Oreodon, but in this genus the posterior facet is much less conspicu- 

 ously developed. In the present species, the shafts of mc. iii and mc. iv are quite 

 heavy and not very long, in which respect they differ very markedly from those of 

 the second species, M. intermedins. In Oreodon, mc. iii not only rises above mc. iv 

 but also extends below it distally, while in Mesoreodon, as in Merychyus, mc. iv 

 extends slightly below the end of mc. iii, though it is considerably the shorter of the 

 two. Proportionately, mc. iv is little, if any, longer in Mesoreodon than in the White 

 River genus, the different disposition of the metacarpals being due to the enlarged 

 unciform process of mc. iii, the greater relative height of the unciform, and the con- 

 sequent downward displacement of the head of mc. iv. 



The fifth metacarpal is quite different from that of Oreodon in having a narrower 

 but deeper head, with the shaft broader proximally, expanding less distally and being 

 more strongly recurved. In length and thickness it is the counterpart of mc. ii, whereas 

 in the White River genus the latter is decidedly stouter. On all of the metacarpals 

 the distal carina? are much better developed than in Oreodon and are plainly visible 

 when the manus is viewed from the front. 



The phalanges of the proximal row are like those of the earlier genera of the 

 family, except that they are relatively shorter. Those of the second row are notably 

 shortened and broadened ; the distal trochlea is wider and not reflected so far upon 

 the dorsal side of the bone, but is more prominent upon the palmar side. The ungual 

 phalanges of this species are very peculiar and different from those of any other 



