SOREX CINEREUS.--It is reasonable to suppose that the cinereous shrew had a continuous range across the forested area of British Columbia in pre-Wisconsin time. Without having been isolated, the dark coastal race (_streatori_) may have developed from the wider-ranging inland _cinereus_, as a response to the denser, humid, coastal forest-habitat, after having been forced southward to Washington by the Vashon Glaciation. Since that time it is presumed to have reoccupied the coast of British Columbia and southern Alaska. This coastal race might have developed in Vashon time, while isolated in southwestern Washington. The Cascades are populated by a race of the Rocky Mountain Fauna, _S. c. cinereus_, which probably entered the Cascades from northeastern Washington or British Columbia in Recent Time. The absence of the species in western Oregon, its rarity in western Washington, and its abundance farther north suggest a northern origin and northward rather than southward postglacial movement. Had the full species _cinereus_ been a preglacial resident of western Washington we would expect _streatori_ or a race related to it to occur in the Cascades. SOREX MERRIAMI.--The periphery of the range of this member of the Great Basin Fauna may have been in southeastern Washington since pre-Wisconsin time. SOREX TROWBRIDGII.--This shrew is a typical Pacific coastal species with an extensive range along the Pacific Coast south of Washington. The Washington population may have been isolated in southwestern Washington during Vashon time or may have crossed the Columbia into Washington from western Oregon early in the Recent. Since the retreat of the ice it has extended northward to southern British Columbia and eastward to the eastern side of the Cascades. Save for crossing the Cascades its postglacial movements have been slight, as is typical of Pacific Coastal species. The race _destructioni_ probably has been isolated on Destruction Island for several thousand years. SOREX VAGRANS.--This species probably has had a continuous range over the western United States since the late Pleistocene. The dark coastal race (_vagrans_) probably was differentiated from the paler races of the Great Basin in response to the more humid climate along the coast. SOREX OBSCURUS.--The history of this shrew of alpine predilection probably corresponded closely to that of _Sorex cinereus_. The derivation of the dark, long-tailed, coastal race (_S. o. setosus_) from the smaller, paler, inland race (_obscurus_) probably occurred before Vashon-Wisconsin Time. _Sorex o. setosus_ is one of a complex of races distributed along the Pacific Coast from Alaska to California.