THE MAMMALIA OP THE DEEP RIVER BEDS. 105 



distal facet for the unciform is more deeply concave in front. Kowalevsky does not 

 figure this bone in the French specimens. 



The pisiform is very different in shape from that of Equus caballus and is more 

 like that of E. burchelli. Compared with the pisiform of the former species, it is 

 very less broadened vertically, is more recurved at the free end, and there is a greater 

 difference in vertical diameter between the proximal and distal ends. The principal 

 cuneiform facet is sessile, not strongly projecting, and is connected by a narrow band 

 with the upper facet. In A. aurelianense this connection is not found, and the cune- 

 iform facet is very prominent, as in Equus, but, on the other hand, the free portion is 

 even more slender and tapering than in the American species. 



The trapezium is not preserved in the specimen, but its presence is demonstrated 

 by the facets upon the scaphoid, trapezoid and second metacarpal. 



The trapezoid is likewise very equine in character, but with some not unimpor- 

 tant differences of detail. The facet for the scaphoid is somewhat less strongly con- 

 vex and continues posteriorly, without interruption, into the small surface for the 

 trapezium. Distally, the divergences between the two genera are more marked. In 

 Equus, behind the large surface for the second metacarpal, there is a facet for the 

 posterior part of the head of inc. iii, and, at right angles with this, a surface for the 

 magnum, the two together forming a conspicuous projection. In A. equinum, on the 

 other hand, the trapezoid has no contact with mc. iii, and the posterior contact with 

 the magnum is very limited and appears not to form a facet. In this species, also, 

 the trapezoid is less completely concealed by the magnum when the carpus is seen 

 from the front. On the ulnar side there are two well-developed facets for the mag- 

 num, which are separated by a narrower interval than in the horse. The trapezoid 

 of the European species is unknown, but the facets on the adjoining bones show that 

 it was very much as in the American form. 



The magnum is, in general, extremely equine, but differs in many minor points 

 from that of existing species. It is higher and narrower in the fossil; the propor- 

 tions of the two proximal facets are about as in the horse, except that the posterior 

 convexity, or head, is very much narrower. As in the existing species^ this head is 

 covered entirely by the lunar and has no contact with the scaphoid. On the radial 

 side of the magnum are two facets for the trapezoid and a small oblique surface for 

 mc. ii ; the posterior trapezoid facet, which is so conspicuous in Equus, does not 

 occur. On the ulnar side, the unciform facets are quite different from those of the 

 horse. In the latter genus the two anterior unciform surfaces are close together and 

 sometimes confluent, and the posterior facet occupies more than half the vertical 

 diameter of the head. In A. equinum all three facets have a much smaller vertical 



