1911] Swarth: Alaska Expedition of 1909. 157 



page 156) ; in fact there is probably hardly another North 

 American species of mammal with so extraordinary a range. It 

 is known to occur on Chichagof, Baranof, Coronation, Warren, 

 Forrester, and Duke islands, in Alaska, and on Prevost Island, 

 at the southern extremity of the Queen Charlotte group. (The 

 Prevost Island mouse has been separated as a slightly differ- 

 entiated subspecies, P. s. prevostensis Osgood, and Forrester 

 Island specimens considered as of this form, but for the purposes 

 of this discussion they may be considered the same.) These 

 islands are most of them widely separated, between Duke and 

 Forrester and between Duke and Coronation and Warren lie 

 whole groups of islands inhabited by a different species (P. m. 

 hylaeus), while those islands nearest to Duke contain still 

 another species (P- m. macrorhinus) . Between Forrester and' 

 Prevost lies the entire group of the Queen Charlotte Islands. It 

 might be argued that the mice of these various islands are really 

 distinct species developed similarly through similar conditions 

 and that their present appearance does not indicate their true 

 relationships, but it is hard to appreciate how these particular 

 islands differ from the scores of others in the region sufficiently 

 to have produced such results. No other Peromyscus has been 

 found on the islands where this form occurs. 



Some interesting comparisons can be drawn regarding the 

 distribution of the species of Microtus and Peromyscus in the 

 southern part, at least, of the Sitkan district. In each the species 

 arrange themselves, roughly, in parallel north and south lines. 

 In the white-footed mice we find on the mainland, and on those 

 islands lying closest to it, a large, robust form, Peromyscus 

 maniculatus macrorhinus. A little farther west, throughout the 

 middle line of islands, reaching the mainland in the northern 

 part of the region, is a much smaller variety of the same 

 species, P. m. hylaeus. Still farther west on the outlying islands, 

 is an exceedingly large mouse, P. sitkensis. This, though con- 

 sidered a distinct species, is apparently but a robust form of the 

 maniculatus group. 



So also with the meadow-mice: Microtus macrurus is the 

 common form of the southern part of the region. Mainland 

 specimens are much the largest, those from the islands inhabited 



