72 BULLETIN OF THE 



ARTIODACTYLA. 



OREODONTID^. 



MERYCHYUS, Leidy. 



Merychyus elegans, Leidy. 



The genus Merychyus is abundant in the Loup Fork, but has been known 

 hitherto chiefly from the dentition. The Gariuan collection contains some 

 portions of the skeleton, which are therefore of great interest. These speci- 

 mens show that the genus has departed but little from the type of the fam- 

 ily, Oreodon, but present, nevertheless, some important approximations to the 

 ruminants. 



The ulna and radius show no tendency to coalesce, and the former has the 

 shaft considerably more reduced than in Oreodon. The radius differs in many 

 ways from the ordinary oreodont type ; tlie groove for the intei trochlear ridge 

 of the humerus is narrower, tlie inner flange of the head smaller and less ob- 

 lique, the outer larger and more concave, and the upward projection from the 

 anterior edge much better developed, almost as in a true ruminant. The sliaft 

 is broader and more flattened, the walls much thiiini;r, and the medullary cav- 

 ity larger. The distal end is less expanded and thickened, and the tendinal 

 sulcus barely indicated. The facets for the scaphoid and lunar are very dis- 

 tinctly separated ; the former is shaped luuch as in Oreodon, but more deeply 

 incised and more obli(piely placed; between the two is a very deep notch, 

 which penetrates from the posterior side through nearly half the thickness of 

 the radius. This notch is indicated in Oreodon, but is not nearly so deep. The 

 only bone of the maims which is preserved is the magnum, the shape of which, 

 however, shows tluit it has moved entirely beneath the scaphoid, and has a 

 deeply concave facet upon its ulnar side which embraces the side of the lunar 

 almost in a semicircle. No facet for the second metacarpal is to be seen upon 

 the radial side of the magnum, whence it follows that the third metacarpal was 

 in contact with the trapezoid, and that an adaptive reduction of the manus had 

 commenced, which, except in Merycochoerus, is unknown in other oreodonts. 



Of the tibia only the distal end is preserved, and this pcn-tion difl'ers but little 

 from that of Oreodon; the astragalar fticets are somewhat more deeply grooved 

 and of more unequal size, and the fibular surface is deeper, as if the distal end 

 of the fibula had commenced to wedge itself between the tibia and the calca- 

 neum. The pes is higher and more slender than in Oreodon, but shows few 

 important changes. The middle and external cuneiforms are united, but the 

 limits of the two elements are plainly shown by the step cut in the distal sur- 

 face. Metatarsal IL occupies the whole of the distal surface of the mesocunei- 

 form, and abuts against the side of the ectocuneiform, while metatarsal IIL is 

 confined to the latter alone. Merychyus thus presents the curious condition of 

 an adaptively reduced manus and an inadaptively reduced pes. The metatar- 



