PERISSODACTYLA. 



331 



identified in the New World, but it abounded in Europe 

 during the Eocene period, the species varying from the size 

 of a hare to that of a Rhinoceros. Closely allied to one 

 another, or absolutely identical, are the forms which have 

 been described under the names of Hyracotherium, Pachy- 

 nolophus, Fliolo'plius, Lo'phiotlicrmm, and Proipalmotlurium. 

 These are Tapiroid genera from the Eocene Tertiary of the 

 European area, in which the transverse ridges of the molars 

 become broken up into transversely-arranged tubercles. 



In the Eocene of North America the place of Lopliiodon 

 and its European allies seems to be taken by Helaletes and 

 Hyrachyus (fig. 632, b). The latter is strongly Tapiroid in 



Fig. 632.— A, The three inohirs and hindmost prwniolar of the upper jaw on the right 

 side of Lopliioclon Isselense, showing the grinding surfaces, Eocene (after Gervais) ; b, Trit- 

 urating surfaces of the molars and prsemolars of Hyrachyus agrarius, Eocene of North 

 America (after Leidy). 



its general characters, having four prsemolars in the u]3per 

 jaw on each side (as in Tcqnrus), and either three or four 

 lower prsemolars. The prsemolars, too, resemble those of 

 Lojiliiodon in being less complex than the molars. In the 

 Miocene of North America few remains of Tcqjiridcc have 

 been discovered, and those that are known aj)pear to belong 

 to the genus Tapiravus. 



We may also provisionally place here a group of American 

 Eocene Mammals (the Limnohyidm of Professor Marsh), 

 which are in many respects allied to the Tapirs, but are at 



