3l8 THE HOLARCTIC REGION. [CHAP. 



fox. Much discussion has taken place with regard to whether any 

 of the bears of North America are distinct from the common brown 

 bear ( Ursus arctus), with its many Asiatic varieties. According, 

 however, to one of the latest memoirs on this subject 1 , all these 

 forms appear mere varieties of the latter, the so-called cinnamon 

 and black bears presenting more distinctly marked differences 

 than does the grizzly. The American marten is so nearly related 

 to the European marten and the Asiatic sable that it is almost 

 impossible to point out valid characters by which the three forms 

 can be specifically distinguished. In the case of the walrus, the 

 Pacific form is distinguished by certain external features from the 

 one inhabiting the Atlantic coasts, although these are scarcely of 

 sufficient importance to be ranked as specific. In regard to the 

 Arctic vole, it may be mentioned that although it is typically a 

 polar form, yet it is represented in southern Europe by the bank- 

 vole (Microtus glareolus) and in the United States by Gapper's 

 vole (M. gapperi\ both of which may be regarded as southern 

 climatic offshoots from the northern stock. Among the other 

 species of rodents it will suffice to mention that the European 

 and American beavers are merely distinguished from each other 

 by the relative lengths of the nasal bones of the skull. And it 

 may be added that the Kamschatkan wild sheep is so closely 

 related to one race of the bighorn, or Rocky Mountain sheep, that 

 it is very questionable whether the two are really entitled to 

 specific distinction. The same is also the case with the two deer 

 mentioned in the list. Reference has already been made to the 

 circumstance that the musk-ox is extinct in the eastern division 

 of the region. A few of the American forms, such as the bear, 

 beaver, bison, and bighorn, enter the limits of the Sonoran region. 



Although, as will be shown immediately, there are a large 

 number of generic types respectively confined to its eastern and 

 western divisions, the lists given above, especially the one relating 

 to the species, are amply sufficient to demonstrate the essential 

 unity of the Holarctic region. None of the other zoological 

 regions have anything like the number of common or representa- 



1 A. E. Brown, Proc. Ac. Philad. 1894, pp. 119, 129. Merriam, P. BioL 

 Soc. Washington, vol. x. pp. 65 83 (1896), regards the N. American bears as 

 forming several distinct species. 



