1894.] 



243 



[Scott. 



tion of the radius with tliat of Oreodon is complete. The shaft has a 

 remarkably strong curvature forward (t. e., with the convexity in 

 fioiit) and is slender with transversely oval section, broadening gradually 

 to the distal end, while in Oreodon it continues slender and expands sud- 

 denly into the inferior end. The distal portion presents many more points 

 of diftcrence between the two genera, than does the proximal and has in 

 Acjriochoerus quite a deceptively carnivore-like appearance. In the latter 

 it is more thickened transversely and less anteroposterlorly than in 

 Oreodon, the scaphoid and lunar facets are less distinctly separated and of 

 different shape and there is no sulcus for the extensor tendons upcm the 

 anterior face of the bone. The ulna has an olecranon shaped much like 

 that of Oreodon and similarl)'- grooved at the extremity, but decidedly 

 thicker and more massive. The inner humer.il facet forms in its distal 

 portion a remarkably prominent fliriug lip, far exceeding the correspond- 

 ing structure in Oreodon. The shaft is large throughout; proximally it 

 is trihedral, but soon becomes much compressed laterally and resembles 

 a rib in shape, since the antero-posterior depth is retained. The distal end 

 is contracted to a narrow and simply convex facet for the cuneiform. 



The carpus is very ditlerent from that of Oreodon. A complete 

 account of it cannot yet be given, the only available specimens 

 lacking the scaphoid and pisiform. The lunar is more like that of the 

 Uinta genus Protureodon than that of 

 the White River form. The special 

 peculiarity of the lunar in the true oreo- 

 donts lies in its tendency to move over 

 upon the unciform and to make its 

 contact with the magnum altogether 

 lateral. This tendency is already be- 

 ginning in Frotoreodon and reaches its 

 culmination in Merycochmrus and 

 Merychyus. In Ayriochcerun, on the 

 other hand, this tendency is reversed ; 

 tlie lunar rests almost entirely upon 

 the magnum, its facet for which is 

 broad and but slightly oblique. The 

 anteri»>r portion of this facet is convex, 

 becoming deeply convex behind. The 

 unciform facet is lateral rather than distal in front, but towards the palmar 

 side the unciform extends beneath the lunar. The radial surface is like 

 that of Orecdon, but does not descend so low upon the dorsal face of the 

 bone, and the palmar portion does not present so much lalerall3\ The 

 cuneiform is relatively large ; proximally it displays a broad concavity for 

 the ulna, while the distal face is occupied by the large subcircular facet for 

 the um iform. The pisiform facet is flat and notably small, whereas in 

 Oreodon it is concave and occupies the whole palmar side of the bone. 

 The trapezium is somewhat of a surprise in its shape and connections ; it 



Fig. 2. Part of left manus of A . major ? 

 Nat. size The trapezium is incorrectly 

 pliced, the surface in contact with the 

 trapezoid being that for the scaphoid. 



