The martens of western Washington (_Martes caurina caurina_) are a coastal race. Those of northeastern Washington belong to a race of the Rocky Mountain Fauna, and are referred to _M. c. origenes_. Davis (1939: 132) refers the martens of Idaho to _Martes caurina caurina_. I have compared specimens from Idaho with animals trapped for fur from the Pacific Coast proper and feel that the animals from northeastern Washington and those from Idaho are more like _origenes_ than _caurina_, although perhaps not typical. The animals from the Pacific Coast proper are _caurina_ and have darker heads and brown instead of yellow patches on the throat. MARTES PENNANTI.--Fishers are found throughout the Cascade Mountains and probably were widely distributed over western North America in pre-Wisconsin Time. MUSTELA ERMINEA.--The distribution of ermines along the coast of northern California and in the Cascade-Sierra Nevada of Oregon and California indicates, as does their differentiation there, that they ranged southward to these areas before and during Vashon-Wisconsin Time. In immediate pre-Vashon-Wisconsin Time, the dark race _streatori_ probably occurred in western Washington. The race _murica_ probably occurred in the Blue Mountains then, as it does today, but probably occurred also in the Cascades of Washington. The descent of the Vashon glaciers probably displaced _streatori_ from the northern part of its range, at least temporarily. In the Cascades, _murica_ was likewise forced southward. Ermines related to the northern _richardsonii_ were forced into northern Washington and Idaho by the Wisconsin ice. They probably were unable to live on the barren, unglaciated plains of eastern Washington but persisted in Idaho. The ranges of the three forms at the maximum extent of the Vashon-Wisconsin may be reconstructed as follows: _streatori_ in southwestern Washington; _murica_ in the southern Cascades and the Blue Mountains; _invicta_ stock in northern Idaho. While so isolated, the ermines of the southern Cascades probably mingled, to a certain extent, with _streatori_ and developed the characters that now separate _gulosa_ from both _murica_ and _streatori_. The intermediate nature of _gulosa_ has been mentioned by Hall (1945: 85). The retreat of the ice allowed _streatori_ to move north and _invicta_ to move north and east into Washington and the northeastern Cascades. To a lesser extent, _gulosa_ may have moved north. The poorly-marked race _olympica_ probably evolved from _streatori_ in the Recent. It is difficult to account for the dark race _fallenda_. It must have evolved from _streatori_ in the Recent but the origin of such a strongly marked race in such a short time is surprising. It might be mentioned that a similarly differentiated race of chipmunk, _Eutamias amoenus felix_, occupies much the same range.