THE MAMMALIA OF THE DEEP RIVER BEDS. 159 



the latter is somewhat smaller and much more oblique in position, being almost as 

 much lateral as proximal and continuing without interruption into the facet for the 

 third metacarpal, which is relatively large. The distal side bears facets for the fourth 

 and fifth metacarpals, of which the latter is unusually large. The posterior hook of 

 the unciform is long and heavy and projects downward and backward, but is not 

 curved laterally. 



In Merycochcerus the metapodials attain a degree of shortness and heaviness 

 such as is found in no other genus of the family, and the lateral digits in particular 

 are relatively very stout, so as to recall in some degree the feet of the hippopotamus. 

 The second metacarpal is short and heavy, with a small head, which bears a narrow 

 convex head for the trapezoid and on the postero-external side a small facet for the 

 magnum. There is no anterior contact with the magnum, this bone being excluded 

 from the second metacarpal by the extension of the third to the trapezoid. On the 

 postero-external angle of the head is a small facet for the trapezium. The shaft is 

 somewhat contracted in the middle and is broadest just above the distal trochlea, 

 which is very unsymmetrical in shape. In M. cuenopus the second metacarpal is 

 decidedly more slender and compressed than in the species before us. 



The third metacarpal is much the stoutest bone of the series and its shaft is of 

 almost uniform breadth throughout, though slightly expanding towards the distal 

 end. The head bears a large number of facets and is very completely and perfectly 

 interlocked with the surrounding bones. On the radial side is a flat, horseshoe- 

 shaped surface for the second metacarpal, and above this a small, triangular facet for 

 the trapezoid, which surface, however, is confined to the dorsal moiety of the bone, 

 dying away towards the palmar side and allowing the second metacarpal to reach the 

 magnum. The magnum facet is deeply concave from side to side and convex from 

 before backward; the antero-external angle is drawn out into a heavy process, which 

 overlaps the head of mc. iv and abuts against the unciform. The posterior facet for 

 the fourth metacarpal is large and somewhat oblique, so as to extend slightly under- 

 neath that bone. The distal trochlea is low and broad; its carina is very prominent 

 but does not extend upon the dorsal side. 



The fourth metacarpal is of about the same length as the third and the shaft has 

 the same antero-posteriorly compressed shape, though it is not so wide transversely. 

 Although the fourth metacarpal is actually no longer than the third, it extends be- 

 yond it distally, for the third rises higher at the proximal end. In Oreodon, mc. iii 

 considerably exceeds mc. iv in length and projects beyond it both proximally and 

 distally. The surface for the unciform is not very broad and towards the palmar 

 side it becomes obliquely lateral in position. The fifth metacarpal is somewhat 



A. P. S. — VOL. XVIII. U. 



