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 liering 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, oyer 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, tire 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. 
