MUSEUM OF COMPARATIVE ZOOLOGY. 73 



sals are relatively very long and slender, more so than in any other member of 

 the entire family, though far from reaching the elongation seen in the true 

 ruminants ; the lateral digits are especially slender, though proportionately as 

 long as ill Oreodon. The phalanges are likewise long and slender, but the un- 

 guals are still plainly of the true oreodont pattern. 



Another specimen of this species is the skull of a very young animal with 

 the milk dentition, which shows some interesting differences from that of Oreo- 

 don. In the latter genus, as in the Tragulina and the older selenodonts gener- 

 ally, the third upper milk molar, cL§, is of a triangular shape, having only the 

 posterior crescents developed, with the anterior portion elongated and tren- 

 chant, while Merychyus agrees with the true ruminants in the fact that this 

 tooth is like a permanent molar, consisting of four crescents. 



Of all known oreodonts Merychyus is perhaps the one which most closely ap- 

 proximates the true ruminant type. This is apparent in the elongated and 

 more or less prismatic crowns of the true molars, in the increased size and com- 

 plexity of pm. 2, in the character of the milk dentition, in the structure of the 

 long bones of the skeleton with their large medullary cavities and thin walls, 

 as well as in the adaptive method of reduction assumed by the manus. 



MERYCOCHCBRUS. 



Merycochoerus cenopus, Scott. 



The type of this species is the specimen consisting of a beautifully preserved 

 manus and pes contained in the Garman collection from the Loup Fork of 

 Nebraska, which unfortunately are not associated with teeth. It is therefore 

 possible that they may belong to some already described species, though they 

 do not agree well in size with any of them. 



The foot structure of this genus has been briefly noticed by Cope, who states 

 that the feet are tetradactyle, and that " the os magnum is entirely beneath the 

 scaphoid, and there is a distinct trapezium. The posterior foot is constituted as 

 in Eucrotaphus." (Proc. Am. Ass. Adv. Sci., 1884, p. 484.) The manus in Mery- 

 cochoerus agrees much more closely with that of Merychyus than with that of any 

 other genus of the family. The carpus is higher in proportion to its breadth 

 than in Oreodon, and very much higher as compared with the height of the meta- 

 carpus, thus giving the manus very different proportions in the two genera. 

 When the individual carpal bones are compared, we find many differences of de- 

 tail. The scaphoid has lost its cuboidal shape and become higher, narrower, and 

 deeper (antero-posteriorly) ; the proximal surface has a convex anterior ridge 

 which is very oblique, rising to a high point on the ulnar, and dying away on 

 the radial side. The distal surface is anteriorly much narrower than in Oreo- 

 don, broadening however behind; the magnum facet is much larger, and the 

 trapezoidal smaller and more lateral. The trapezium appears not to have been 

 in contact with the scaphoid. The lunar is very peculiar, especially in the great 

 downward prolongation of the beak-like process, which is wedged in between 

 the unciform and magnum, and almost reaches the metacarpals. The proximal 



