72 ON THE EXTINCT MAMMALIA OF 



What are supposed to be the bones of the fore arm and leg are discrete, as in the 

 Hog, and the bones of the feet correspond in number with those of this animal. 



The species belonging to this family I have referred to four genera, which are 

 closely allied, and indeed are not separated by any very striking characters. Perhaps 

 most naturalists would include them in a single genus, nor am I prepared to dispute 

 such a view. 



The genera are named Oreodon, Merycochoerus, Merychyus, and Leptaiichenia. 



The first genus, Oreodon, includes three species, besides several douljtful ones, or 

 well-marked vai'ieties. Their remains are by far the most abundant of those which 

 have been brought from the Mauvaises Terres of White River. Occurrmg most fre- 

 quently in bed B of Dr. Hayden's section of the miocene formation, they also extend 

 into the higher beds C and D of the same section. Oreodon CulherUoni and 0. gra- 

 cilis especially belong to the lower bed B, but 0. major appears to have been a 

 rather later form, and belongs to the higher bed D. 



Merycochoerus belongs to the latter bed, and looks as if it might have been a 

 derivative of its cotemporary 0. major. 



Merychyus is represented by three species, the remains of which were obtained from 

 bed F of Dr. Hayden's section of the pliocene formation of the Niobrara River. 

 These look as if they might have been derived, perhaps by selection, according to the 

 view of Darwin, from one or other of the species of Oreodon of the preceding period, 

 from Merycochoerus, or from the succeeding genus. 



Leptaiichenia is represented by three species, the remains of which pertain to bed 

 D of Dr. Hayden's section. 



OREODON. 



Of the great variety and abundance of mammahan fossils brought from the 

 Mauvaises Terres of White River, by far the most numerous belong to a remarkable 

 and pecuUar genus of ruminants, which we have distinguished by the name of 

 Oreodon. In the various collections of fossils from the locality mentioned which have 

 been submitted to my inspection, I have estimated that I have observed skulls, frag- 

 ments of others and teeth, together vdth other bones of the skeleton, of perhaps five 

 hundred individuals of Oreodon, referable to three distinct species. With compara- 

 tively few exceptions, the specimens belonged to a species of intermediate size, to 

 which I have given the name of Oreodon Cidhertsoni. Those of the largest species, 

 Oreodon major, are rare, comprising not moi'e than one or two per centum of the 

 whole. Specimens of the smallest species, Oreodon gracilis, are more abundant, — 

 equal to about ten per centum of the whole. 



Oreodon, in the anatomical character of its skeleton, exhibits a clear relationship to 

 suilline anunals, and, indeed, the character of the genus cannot probably be better 



