_Range._--Mainland of southeastern Alaska from Lynn Canal south to include Mitkof, Zarembo, Wrangel and Revillagigedo islands. See figures 25, 26 on pages 95 and 134. _Characters for ready recognition._--Differs from _M. e. arctica_ and _haidarum_, in both sexes, by proximal two-thirds of under side of tail colored same as upper parts rather than same as underparts and interorbital breadth less, instead of more, than distance between glenoid fossa and posterior border of external auditory meatus; from _M. e. salva_, in males, by overall depth of braincase including tympanic bullae less than 89 per cent of orbitonasal length, females not individually distinguishable but averaging shallower through the braincase; from _M. e. initis_, _celenda_ and _seclusa_ by interorbital breadth less than distance between glenoid fossa and posterior border of external auditory meatus (females of _initis_, _celenda_ and _seclusa_ unknown); further from _initis_ by total length less than 317 and black tip of tail less than 57 per cent of length of tail-vertebrae; further from _celenda_ by chest white, not mostly covered by brown patch. _Description._--_Size._--Male: Eight adults from Windham, Alaska, yield average and extreme measurements as follows: Total length, 298 (288-315); length of tail, 88 (84-94); length of hind foot, 41.3 (37-44). Female: Two adults from Juneau and Helm Bay measure, respectively, as follows: Total length, 258, 258; length of tail,----, 76; length of hind foot, 32, 34. _Color._--As described in _Mustela erminea richardsonii_ except that least width of color of underparts averaging, in five females, 42 (35-53) per cent of greatest width of color of upper parts. Black tip of tail in same specimens averaging 36 (30-40) mm. which is 49 (48-53) per cent of length of tail-vertebrae. _Skull._--Male (based on 8 adults from Windham): See measurements and plates, 2-4. As described in _Mustela erminea richardsonii_ except that: Weight, 1.8 (1.5-2.6) grams; basilar length, 37.5 (36.5-38.9); length of tooth-rows more or less than (about same as) length of tympanic bulla. Female (based on 5 adults, from localities listed in the table of cranial measurements): See measurements and plates 9-11. As described in _Mustela erminea richardsonii_ except that: Weight, 0.96 (0.7-1.1) grams; basilar length, 32.7 (31.9-33.2); breadth of rostrum more or less than (about equal to) 30 per cent of basilar length.