TAMIASCIURUS HUDSONICUS.--The two species of red squirrels, _T. hudsonicus_ and _T. douglasii_, are specifically distinct and probably became differentiated in the Pleistocene when southward moving glaciers cut in two the range of the ancestral stock. The morphological differences are too great, comparatively, to have occurred during the Vashon-Wisconsin Divergence. _T. hudsonicus_ probably occupied a range in pre-Wisconsin Time that included the Rocky Mountains and areas to the north. Glacial ice probably restricted the range of _hudsonicus_ in Wisconsin Time but after the retreat of the ice _hudsonicus_ moved northward to reoccupy its former range. It also moved westward across northern Washington to the Cascades, where it met the range of _douglasii_. Farther north, it moved westward to the Pacific, thus occupying an area that, in pre-Vashon time, probably was occupied by _douglasii_. TAMIASCIURUS DOUGLASII.--The Douglas squirrel probably occupied the coastal region of Oregon, Washington and British Columbia in pre-Vashon Time. The descent of the ice restricted its range to southwestern Washington and areas to the south. After the retreat of the ice it moved northward somewhat but, like other coastal species, the movement was slow. Meanwhile _hudsonicus_ from the Rocky Mountain Fauna, had spread to the coast of British Columbia. GLAUCOMYS SABRINUS.--This flying squirrel is a plastic species. It inhabits all of the forested parts of Washington. The distributional picture presented by the 5 races (Fig. 92) which occur in Washington is complicated. The ranges of 3 of these lie principally outside the state of Washington. The race _oregonensis_ occupies Washington and Oregon west of the Cascades; _fuliginosus_ occupies the Cascades of Washington, Oregon and southern British Columbia; _columbiensis_ occupies the interior valleys of British Columbia and adjoining Washington; _latipes_ occupies the northern Rocky Mountains of British Columbia, northern Idaho and extreme northeastern Washington; and _bangsi_ occupies the Blue Mountains of Washington and Oregon and a wide range in Idaho and eastward.