PRONG-HORN ANTELOPE 113 



" Deep River " deposits of Montana in middle or lower 

 Miocene, and persisted until the Pliocene. During the latter 

 period several new genera, viz. : Capromeryx, Platatherium 

 and Leptotherium, branched off from the ancestral sk>ck, and 

 made their way into newly-opened areas. The last two have 

 occurred in recent beds in Brazil, the other in Nebraska. 

 Thus the family Antilocapridae to which the recent prong- 

 horn and all these fossils belong, originated in America and 

 never left it. 



Among the birds of the Rocky Mountains the dippers are 

 very characteristic. They are quite unrepresented on any 

 of the eastern mountain systems, being also absent from 

 Greenland and Labrador. In the Old World they are more 

 or less confined to the mountains, but not nearly to the same 

 extent as in America. In my " European Animals "* I have 

 already cited Dr. Stejneger's interesting article on the geo- 

 graphical distribution of the dippers (Cinclus), and I may 

 again briefly summarise the results of his studies. He places 

 the origin of the genus on the great plateau adjoining 

 northern India. At the dawn of the Tertiary Era the species 

 radiated from this centre east and west. America being then 

 connected by land with northern Asia, the ancestors of the 

 present dippers had special facilities for crossing to the New 

 World from Asia. They are supposed to have spread since 

 along the Rocky Mountains and Andes to the very furthest 

 end of South America. Dr. Stejneger's theoryf certainly ex- 

 plains the existing range of Cinclus in a satisfactory manner, 

 but there seems to me still another view of looking at the 

 problem. If, as I believe, the Atlantic Ocean was bridged 

 over by land in the direction of southern Europe in early 

 Tertiary times, it is possible that the dippers may have been 

 introduced into the New World in that manner. At any rate, 

 the problem is worth considering from that point of view, 

 when the dippers come to 'be worked 0'U,t in .a, thoroughly 

 systematic way. Among the older forms of both animals and 

 plants there are in western America a surprisingly large 

 number of groups which are closely related to European ones. 



* Scharff, E. F., " European Animals," p. 200. 

 t Stejneger, L., " Geographical Distribution of Cinclus," p. 425. 

 L.A. i 



