HISTORY OF THE PERISSODACTYLA 



341 



proposed by Professor Osborn, in order to avoid, so far as 

 possible, the confusing effect of different methods of classi- 

 fication. 



As before mentioned, the subfamily of the fhyracodonts 

 (fHyracodontinse) became extinct in White River times, during 





Fig. 180. — t Cursorial rhinoceros {<! Hyracodon nebrascensis) , White River stage. Re- 

 stored from a skeleton in the Museum of Princeton University. 



most of which it was represented by the single genus ]Hyra- 

 codon, whence are derived the names for the family and sub- 

 family. The series was purely North American, and no mem- 

 ber of it has ever been found in any other continent. The 

 species of \Hyracodon were altogether different in appearance 

 and proportions from the true rhinoceroses, being lightly 

 built, slender, cursorial creatures, suggestive rather of horses 

 than of rhinoceroses, to which they bore much the same rela- 

 tion as the slender-limbed, narrow-footed flophiodonts did to 

 the tapirs (see p. 326) ; in size, they were somewhat taller and 

 considerably heavier than a sheep. 



The low-crowned grinding teeth had the unmistakable 

 rhinoceros-pattern, and between them and the teeth of the 



