ASIATIC AFFINITIES OF ALASKA 85 



Dr. Allen * considers the inter-relationship of the boreal 

 mammals inhabiting North America and northern Asia so 

 intimate that it could only have been brought about by the 

 existence of a geologically recent land bridge connecting the 

 two areas. He thinks that most of the more northern forms 

 of mammal life on the two continents are probably the slightly 

 modified descendants of types which formerly had a con- 

 tinuous circumarctic distribution, and which have become 

 slowly differentiated, mainly, no doubt, since the disruption 

 of the former land connection at Bering Strait. 



Every naturalist who casually surveys the boreal fauna 

 of North America and northern Asia must be struck by the 

 apparently large predominance of Asiatic invaders in North 

 America, such as the moose, bison, wapiti deer, American 

 wild sheep, glutton, brown bears, the now extinct mammoth 

 and many others, over the American element in Asia. In 

 fact, we scarcely recognise any signs of an exodus having* 

 taken place in the opposite direction. Typically American 

 mammals, such as the common American musk-rat, the por- 

 cupine, the black bear, and others, for example, have repre- 

 sentatives in Alaska, nevertheless they are quite unknown 

 on the western shores of the Bering Sea. At the same time 

 Dr. Allen draws our attention to the occurrence along the 

 Siberian and Kamchatkan coasts of certain mammalian types 

 that are of distinctly American origin. These are a species 

 of weasel (Putorius pygmaeus) closely related to the arctic 

 American weasel (Putorius rixosus),.and only remotely akin 

 to any Eurasiatic species; a spermophile (Citellus buxtoni), 

 closely allied to the boreal American Citellus paryi ; the Kam- 

 chatkan bighorn (Ovis nivicola), which is more nearly related 

 to American forms of sheep than to Asiatic ones, and several 

 others. 



Whether the presence of these closely connected forms on 

 both sides of Bering Strait proves the case of an American 

 invasion of Asia appears to me still somewhat doubtful, 

 especially as the sheep (Ovis) is, as far as we know, of Old 

 World origin. A sheep is known from the Pliocene Forest 

 Bed of England, while it only appeared in America in 



* Allen, J. A., " Mammals from North-Eastern Siberia," p. 183. 



