71(5 



THE EOCENE FAUNA. 



greater specialization than the latter group in the structure of its feet, i. e., 

 the distal metapodal keels are completed forwards, as in most ruminants. 



The similarity of the modifications which have supervened on the 

 Artiodadyle and Perissodacfi/lc lines, in attaining their most specialized 

 extremes, has often been noticed. I repeat them here in tabular form in 

 three columns.* These show (Table I) the modifications in which the Eqiddm 

 and Bovidce are identical, or nearly so, which place them at the heads of their 

 respective orders; Table II, those in which the Equidce are the more special- 

 ized of the two; and Table III, those in which the Bovidce display the highest 

 differentiation. 



ARTIODACTYLA. 



Members of this order were very few in number in the true Eocene 

 periods, so far as our present knowledge extends. The great subdivision of 

 the Ruminantia did not exist, the only types being the Suillines and the 

 Eiirytheria. The characteristics of these groups will be more fully defined 

 in Part Second of this work, which treats of the White River epoch, during 

 which both of the divisions in question were numerously represented. 



OMNIVORA. 

 Two, and perhaps three, genera of hogs from the Eocene beds of our 

 Western regions have come under my notice. They differ from all existing 

 members of the suborder in the anisognathous chai-acter of their molar 



