XI PALEONTOLOGY AXD 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 Ungidatcc (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 Coryphodcn appears 

 to have been allied to the Miocene and later 

 Tapirs, while PliolopJius, 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 Arctogseal province 

 to forbid the supposition that they stood m 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 Arctogsea at the 

 commencement of the Tertiary period. But if 

 we now cross the firontier between the Cainozoic 

 and the Mesozoic faunae, as they are preserved 

 within the Arctoggeal area, we meet with an 

 astounding change, and what appears to be a 



