ix.] PALEONTOLOGY AND EVOLUTION. 209 



mammalian Fauna contains Bats, two genera of Garni- 

 vora, three genera of Ungulata (probably all perisso- 

 clactyle), 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 Pliolo- 

 phns, in its skull and dentition, curiously partakes of 

 both artiodactyle and perissodactyle 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 

 Arctogoea at the commencement of the Tertiary period. 

 But if we now cross the frontier between the Caino- 

 zoic and the Mesozoic faunae, as they are preserved 

 within the Arctogseal area, we meet with an astound- 

 ing change, and what appears to be a complete and 

 unmistakable break in the line of biological continuity. 



Among the twelve or fourteen species of Mammalia 

 which are said to have been found in the Purbecks, not 

 one is a member of the orders Cheiroptera, Rodentia, 

 Ungulata, or Carnivora, which are so well represented 

 in the Tertiaries. No Insectivora are certainly known, 

 nor any opossum-like Marsupials. Thus there is a vast 

 negative difference between the Cainozoic and the Meso- 

 zoic mammalian faunae of Europe. But there is a still 

 more important positive difference, inasmuch as all these 

 Mammalia appear to be Marsupials belonging to Aus- 

 tralian groups, and thus appertaining to a different 



