Female (illustrated by 5 adults): See measurements and plates 12-14. As described in _Mustela erminea richardsonii_ except that: Weight, 0.59 (0.53-0.65) grams; basilar length, 28.1 (27.8-28.4); breadth of rostrum ordinarily more than 30 per cent of basilar length. In comparison with _streatori_, skulls of males and females average smaller in every cranial measurement taken. Teeth of about same size and males 9 per cent, and females 8 per cent, lighter. In relation to basilar length, skull of female shallower, tympanic bullae slightly shorter and, on the average, zygomata less expanded. In comparison with _muricus_, males average larger in every measurement taken; 23 per cent heavier; in relation to other dimensions, braincase shallower at anterior end of basioccipital. Females are of about equal size; in relation to other dimensions, braincase shallower and mastoid and zygomatic breadths less. Comparisons with _invicta_ and _fallenda_ have been made in the accounts of those subspecies. _Remarks._--This is not a strongly marked race and in most of the characters used for differentiating it from other races it resembles either _streatori_ to the west or _muricus_ to the southeast. Nevertheless, there is a geographic area, the southern Cascades of Washington, throughout which individual characters are combined in essentially the same way and there are a few features, for instance, smaller skull of the female, in which _gulosa_ differs from either of its close relatives. In view of these circumstances and because the animals can not well be included in the subspecies _streatori_ or _muricus_, _gulosa_ is recognized as distinct. The races _gulosa_ and _olympica_ are what might be termed weakly differentiated subspecies in contrast to the strongly differentiated subspecies _streatori_ and _muricus_. Of the 21 specimens in winter pelage, 17 are white and four are brown. The brown winter coat is distinctly paler, with more of a smoky tinge, than the brown summer pelage. The light-colored underparts are narrower than in the subspecies immediately to the east but are wider than in the coastal forms to the west. The dark color of the upper parts extends onto the chest in front of the forelegs, as in the coastal forms, in only one of the 13 specimens in summer pelage and in it on one side only. The black tip of the tail is short as in the coastal forms. One specimen is in transitional pelage. It has acquired approximately half of the white winter pelage and was taken on October 12, 1897, at Keechelus Lake. _Specimens examined._--Total number, 38, arranged by counties from north to south. Unless otherwise indicated, specimens are in the U. S. National Museum.