HISTORY OF THE PERISSODACTYLA 357 



not yet been lost, the third or median digit being the longest 

 of the series. In the hind foot, which had only three toes, the 

 departure from the perissodactyl arrangement had already 

 begun, and the third and fourth digits {i.e. of the original five) 

 were of nearly equal size, both in length and thickness, while 

 the second was smaller. 



The family is represented in the John Day, or upper Oligo- 

 cene, by specimens which are sufficiently characteristic to 

 prove that they are properly referable to this group. They 

 have been assigned to the same genus as that of the lower 

 Miocene, but whether the identification is justified remains 

 to be determined. 



In the lower White River beds of Canada is found a much 

 smaller animal of this family, but the material is too fragmen- 

 tary for generic identification. Something more is known of 

 a genus {] SchizotheriuJii) from the European Oligocene, like- 

 wise much smaller than the Miocene and Pliocene forms, 

 which had four, or possibly even five, functional digits, in the 

 manus, but it has not been ascertained whether the trans- 

 formation of hoofs into claws had already taken place. 



It is not yet practicable to determine the relationships of 

 the European and American fchalicotheres to one another, 

 because of the imperfect nature of most of the material. 



The molar teeth of the fchalicotheres were suggestively 

 like those of the ftitanotheres, and, were the teeth alone to be 

 taken into account, no one could hesitate to regard the two 

 families as closely related. 



The most ancient known member of the family is the genus 

 ^Eomoropus, from the Bridger Eocene, which will be described 

 by Professor Osborn in a paper soon to appear. \Eomoropus 

 was much nearer to the normal perissodactyls than were the 

 genera from the Oligocene and Miocene above described. 



