MIGRATION OF TERRESTRIAL VERTEBRATES 313 



The last periods of the Oligocene (Aquitanian) 

 correspond to a rupture of the connection between 

 the two countries. But the connection is renewed 

 at the commencement of the Miocene by the emigra- 

 tion into Europe of the Anchitherium at the Burdiga- 

 lian epoch, of the Titanotheridce (Leptodon) and of 

 the Hipparion in the upper Miocene. However, 

 it is not impossible that these last genera may have 

 come from America by way of China and the 

 Asiatic continent, that is, through the region of 

 Behring Straits. A proof of this is seen in the 

 abundance of Hipparion and other Tridactyl 

 Equidae in the Miocene deposits of the North of 

 China and the foot of the Himalayas. Should this 

 last supposition be correct, it must be admitted 

 that the separation of North America and Europe 

 was definitive from the middle Miocene till the end 

 of Tertiary times. 



We have just recorded the existence of at least 

 seven Tertiary migrations, all in the same direction, 

 that is, from the United States towards Europe. 

 But as a compensation other families of Mammals 

 took at the same epoch the contrary direction, from 

 Europe to America. Indeed, the American White- 

 River epoch, which corresponds to the Oligocene in 

 Europe, shows us the arrival in America of the 

 Anthracotheridce (Ancodus), of the Tragulidce, of the 

 Castoridce (Steneofiber), of the Cricetidce, of the 

 Canidae (Galecynus), of the Mustelidce (Palceogalus), 

 and of the great Felines of the type Machairodus 

 (Dinictis). A second emigration of European forms 

 is manifest in the Miocene of John Day and of Deep 

 River, where we see appear in America the Cervulidae 



