GEOLOGICAL SUEVEY OF THE TERRITORIES. 347 



crown is an inch in breadth fore and aft. The species I have distinguished 

 by the name heading this article. 



Mingled with the remains of 0. superbus are a few fragments, appa- 

 rently referable to 0. Culbertsoni. 



MERYCOCHGERUS. 



As the name of the genus indicates, a ruminating hog, like oreodon, 

 and pertaining to the same family. It is closely related to the latter 

 genus, and perhaps by many naturalists would be regarded as the same. 

 Its chief differences consist in the proportionately great depth of the 

 infra-orbital arch, the abruptly-narrowed face, the comparatively-shallow 

 lachrymal depression, and the more posterior position of the infra-orb- 

 ital foramen. The characters thus presented were more sharply defined 

 previous to the recent discovery of a second species of the genus, 

 which is intermediate, and therefore still more nearly approximates the 

 two genera, if it does not merge the one into the other. 



Merycochoerus proprius — Theremainsof this species were discovered by 

 ProfessorHayden, during Warren's expedition of 1857, on the head-waters 

 of the Niobrara Eiver, opposite Fort Laramie. They were embedded in a 

 dull, reddish-brown sandstone, which Professor Hay den refers to the mio- 

 cene tertiary period. The animal was larger than any of the species of ore- 

 odon, except the 0. superbus of Oregon, which it approximated in size. 

 The jaws are of more robust proportions than in the oreodon s, and the 

 infra-orbital arches of greater depth. In this the latter measure nearly 

 two inches; in 0. supcrbus, an animal of about the same size, an inch and 

 a half; in 0. major, three-fourths of an inch. 



MerycocJicerus proprius appears not to have inhabited the same local- 

 ities with the oreodons, at least cotemporaneously. I suspect it to have 

 lived at a later period, and perhaps, on the theory of the distinguished 

 philosopher Darwin, may have been the successor by selection of the 

 oreodons. 



Merycoclimrus rusticus. — A second species of the genus distinguished by 

 his name is indicated by remains recently discovered by Professor Hayden, 

 on the Sweetwater Eiver, eighteen miles west of Devil's Gate, Wyoming 

 Territory. The animal was about the size of Oreodon major, but is readily 

 distinguishable through the anatomical characters that separate the two 

 genera to which they belong. The number of remains of M. rusticus ob- 

 tained during a short period from a circumscribed locality indicate the 

 animal to have been abundant. 



MERY^CHYTJS. 



Another genus of the oreodont family to which the above name has 

 been given is indicated by a comparative abundance of remains discov- 

 ered by Professor Hayden during Warren's expedition in 1857. The 

 fossils were found in the loose sands of the Mobrara Eiver, and are 

 regarded by Professor Hayden as being of more recent date than those 

 of the oreodons, the age of the formation being considered as later ter- 

 tiary or pliocene. 



Merychyus is clearly related to oreodon and Merycochcerus, and, like 

 the latter, most probably is the successor of oreodon. The construction 

 and form of the skull and teeth are nearly alike in all the genera men- 

 tioned. 



The true molars or grinding teeth of Merychyus are constructed on 

 the same plan as in all ordinary ruminants, recent and extinct, and are 

 intermediate in character with those which have short crowns, as in the 



