XI PALEONTOLOGY AND EVOLUTION 377 



great, while the remains of Middle Eocene and 

 Older Eocene Mammals are comparatively few. 

 The general facies of the Middle Eocene' Fauna, 

 however, is quite that of the Upper. The Older 

 Eocene pre-nummulitic mammalian Fauna con- 

 tains Bats, two genera of Carnivora, three genera 

 of Ungulata (probably all perissodactyle), and a 

 didelphid Marsupial; all these forms, except 

 perhaps the Bat and the Opossum, belong to 

 genera which are not known to occur out of the 

 Lower Eocene formation. The Coryphodon appears 

 to have been allied to the Miocene and later 

 Tapirs, while Plioloplius, in its skull and dentition, 

 curiously partakes of both artiodactyle and perisso : 

 dactyle characters; the third trochanter upon 

 its femur, and its three-toed hind foot, however, 

 appear definitely to fix its position in the latter 

 division. 



There is nothing, then, in what is known of the 

 older Eocene mammals of the Arctogaeal province 

 to forbid the supposition that they stood in an 

 ancestral relation to those of the Calcaire Grossier 

 and the Gypsum of the Paris basin, and that our 

 present fauna, therefore, is directly derived from 

 that which already existed in Arctogaea at the 

 commencement of the Tertiary period. But if 

 we now cross the frontier between the Cainozoic 

 and the Mesozoic fauna?, as they are preserved 

 within the Arctogseal area, we meet with an 

 astounding change, and what appears to be a 



