154 University of California Publications in Zoology. [Vol. 7 



northern derivation. Here the big Alaska brown bears find their 

 southern limit at Frederick Sound and Christian Sound. 

 Microtus sitkensis is closely related to more northern forms, while 

 M. admiraltiae is curiously enough an offshoot of an inland 

 species {M. drummondi) that reaches the Alaskan coast at very 

 few points — one of them being that part of the mainland most 

 closely adjacent to Admiralty Island. 



The central group of islands, though extending to the western 

 edge of the archipelago, is nevertheless but narrowly separated 

 from the mainland, and it contains one characteristic mainland 

 mammal (Sciurus) that does not occur on either the northern or 

 the southern group. (See text figure 1, page 153.) These islands 

 centrally located, are in a sense a meeting ground of the faunas 

 of the surrounding regions. Besides the aforementioned squirrel 

 they contain the sooty grouse found on the islands to the north 

 but not on those directly southward, and also the black bear, of 

 which the reverse is true. 



The southern group is distinguished by the absence of the 

 red squirrel, and the presence of the black bear and wolf, which 

 find their northern limit on the islands at Frederick Sound ; but 

 the most conspicuous feature of this group is the fact that on 

 these islands the spruce grouse (Canachites) occurs, to the 

 exclusion of the sooty grouse {Dendragapus^ , of general distribu- 

 tion elsewhere in the region. (See text figure 2, page 155.) 



The islands lying east of Clarence Straits are mostly but 

 slightly separated from the m^nland, and contain many main- 

 land forms — Evotomys on Wrangell and Revillagigedo, Synap- 

 tomys on Wrangell, Zapus and Fiber on Revillagigedo, Erethizon 

 on Btolin and "Wrangell, Sciuropterus on Etolin, and Sciurus on 

 all of them. That the jumping mouse of Revillagigedo Island 

 should prove to be of the Zapus hudsonius group seems remark- 

 able, as this is hundreds of miles south of the previous known 

 range of this species and as an entirely distinct species occurs at 

 intervening mainland points. 



Coronation and Warren, two small outlying islands west of 

 Prince of Wales, present some curious and interesting conditions. 

 Coronation lies close to Kuiu, and Warren close to Prince of 

 Wales, being more widely separated from one another than they 



