FAUNA OF THE ALEUTIAN ISLANDS AND ALASKA PENINSULA 265 



2437 of Leningrad Acad. Sci.) from St. Paul Island, and no. 2370, the 

 latter is seen to differ in wider (labial to lingual side) molars, seemingly 

 broader rostrum and certainly less continuous ridge on unicuspid. In S. 

 pribilofensis there is a ridge continuous from the tip of the unicuspid on 

 down into the cingulum without a break, whereas in no. 2370 from Unalaska 

 there is a notch, or break, in this ridge where it meets the cingulum, al- 

 though the notch is shallower than in a specimen of Sorex tundrensis (no. 

 39710, Mus. Vert. Zool., from Barrow, Alaska ) which may be said to have 

 a distinct notch separating the internal ridge from the cingulum. In no. 

 2370 the pigmentation stops short of the cingulum. The holotype of Sorex 

 hydrodromus agrees with no. 2370 in the presence of the notch and in the 

 extent of the pigmentation. Nevertheless, in the holotype of hydrodromus 

 the molar teeth are narrower than in no. 2370 and about the same width 

 as in Sorex pribilofensis. 



My conclusion is that Sorex hydrodromus is a recognizable kind (species 

 or subspecies) of Sorex best placed in the arcticus group. In structure of 

 unicuspids it bridges the gap between S. tundrensis and S. pribilofensis. If 

 specimens from the base of the Alaska Peninsula are morphologically 

 intermediate between S. hydrodromus and populations of S. tundrensis east 

 of the base of the Alaska Peninsula, perhaps S. hydrodromus should be 

 treated as only subspecifically distinct from S. tundrensis — otherwise as 

 a full species. To judge from measurements (published by Ognev in Vol. 

 1 of his "Mammals of the U. S. S. R.", 1928) of the various subspecies of 

 Sorex ultimus, S. hydrodromus is a smaller animal. 



In a further communication, Hall expressed the opinion that 

 hydrodromus probably should rank as a full species rather than 

 as a subspecies. In that connection, it is interesting to note that 

 from Unalaska to the Bristol Bay region there are hundreds of 

 miles of territory from which no specimens of saddle-backed 

 shrews have been taken. This would indicate ample isolation on 

 Unalaska for the formation of a species. 



Sorex obscurus: Dusky Shrew 

 Sorex obscurus shumaginensis 



Unalaska -.Chichimukthah (Wetmore) 



In southwestern Alaska, this shrew has a range that is roughly 

 coextensive with that of S. c. hollisteri. About 200 specimens are 

 available in the Fish and Wildlife Service collection, some of 

 which are from the following localities: Nushagak River, Kakwok, 

 Lake Aleknagik, Ugaguk River, Dillingham, Cold Bay, Becharof 

 Lake, Katmai, Chignik, King Cove, Morzhovoi Bay, Port Moller, 

 Frosty Peak, Izembek Bay, Unimak Island, and the Shumagins. 

 In 1937, on Sanak Island, I obtained a shrew that proved to be 

 shumaginensis. 



In the field, w T e noted that this shrew was about as abundant as 

 hollisteri, and that it inhabited grassy areas and wet places. 

 Wetmore reported it to be especially abundant along little streams. 



