Intergradation with _richardsonii_ is complete and gradual; in one sense _invicta_ is but little more than a small _richardsonii_. Intergradation with _fallenda_ is shown by several specimens. These two races differ in large degree in color, and in size and shape of the skull of females. Although the geographic area where intergradation in color occurs is fairly wide, the area in which intergradation in cranial characters in females occurs, appears, from the inadequate material available, to be much narrower. Intergradation occurs freely in Washington with _streatori_ but with _muricus_ so far as known only in the Bitterroot and nearby mountains of northwestern Montana. The Snake River Plains and low country along much of the Columbia River appears to be uninhabited by weasels of the species _erminea_ and hence there is opportunity for intergradation only in the mentioned area of Montana. _Specimens examined._--Total number, 177, as follows. Arranged alphabetically by provinces and states then by localities from north to south in each province and by counties from north to south in each state. Unless otherwise indicated, specimens are in the United States National Museum. =Alberta.= Jasper House, 4[77]; Shovel Pass, 2[77]; Jasper Park, 10[77]; head of Smoky River, 9; Henry House, 2 (1[77]); Blindman River, 1[2]; forks of Blindman River and Red Deer River, 2 (1[60], 1[75]); "near Red Deer, Red Deer River," 1[77]; Red Deer River, 2 (1[2], 1[60]); Red Deer, 2[60]; Rosebud, 2[77]; Prairie, 3000 ft., 1; Didsbury, Little Red Deer River, 1; Canadian Nat'l Park, 1[60]; Canmore, 1; Banff, 1[60]; High River, 1[86]; "Waterton Lake Park" in Alberta, 6[77]. =British Columbia.= Grand Forks of Fraser River, 1; Canoe River, 1[77]; Field, 1; Glacier, 1[58]; E side Beaverfoot Range, 4000-4500 ft., 6 mi. SE Fraser Creek, 8[74]; Wentworth Lake, 1[31]; Revelstoke, 2 (1[77], 1[60]); Spillimacheen[e]en River, 2[2]; Sicamous, 2; Albert River, 7000 ft., 1[2]; Lumby, Creighton Valley, 1[31]; Okanagan, 4 (2[75], 1[94], 1[2]); Kettle River Lake, Gold Range, 4000 ft., 1; Crows Nest Station, 1[74]; Yale District, 3; Fort Hope, 1; Chilliwack Lake, 1[77]; Skagit, 2 (1[77], 1[31]); Skagit Valley, 1[77]; Skagit Summit, 1[77]; Lightning Lakes, 2 mi. N International Boundary, 3; Osoyoos-Bridesville Summit, 2; Westbridge, 1[77]; Rossland, 5[77]; Creston, mouth Goat Creek, 3[77]; Yahk, 4[77].