_Description._--_Size._--Male: Twelve adult and subadult males from Aitkin, Minnesota, yield average and extreme measurements as follows: Total length, 316 (291-341); length of tail, 87 (70-101); length of hind foot, 43 (40-44). Two adults from Aitkin each weigh 170 grams.
Four adult and subadult females from Elk River and Fort Snelling, Minnesota, yield average and extreme measurements as follows: Total length, 249 (240-260); length of tail, 61 (55-65); length of hind foot, 32 (30-33).
_Color._--As described in _Mustela erminea richardsonii_ except that, least width of color of underparts averaging, in males from Minnesota, 32 (19-51) per cent of greatest width of color of upper parts. Black tip of tail in 12 male topotypes in white winter pelage averaging 52 (45-58) mm. which is 60 (53-66) per cent of length of tail-vertebrae.
_Skull._--Male (based on adults from Aitkin): See measurements and plates 2-4. As described in _Mustela erminea richardsonii_ except that: Weight of 2 adults from Aitkin, 2.2, 2.3 grams (9 subadults from T. 61 N, R. 26 W, average 1.95 grams); basilar length, 39.7 (38.5-40.7); length of tooth-rows rarely more (usually less) than length of tympanic bulla.
Female (based on adults from Minnesota as listed in table of cranial measurements, which see): See plates 9-11. As described in _Mustela erminea richardsonii_ except that: Weight, of a subadult from T. 61 N, R. 26 W, 0.91 grams; basilar length, 32.8 (31.8-33.6); breadth of rostrum rarely equal to as much as 30 per cent of basilar length.
From _richardsonii_, topotypes of _bangsi_ differ in that cranial measurements in males are approximately 7 (5-9) per cent less, linear measurements of teeth are 10 (9-11) per cent less and the skull is a fifth lighter. In relation to basilar length the tympanic bullae of _bangsi_ are longer. Skulls of females are individually indistinguishable, those of _bangsi_ averaging approximately 1 per cent less in linear measurements. Comparison with the smaller cicognanii is made in the account of that subspecies.
_Remarks._--Before the subspecific name _bangsi_ was proposed, individuals of this subspecies ordinarily were recorded in the literature as _Mustela cicognanii_. The best single lot of material is in the zoölogical collection of the University of Wisconsin. The late naturalist Albert Lano preserved a large share of the material from Minnesota. The large series from Elk River of that same state was mostly collected by Bernard Bailey although his Aunt, Anna (Bailey) Mills, and her brother the late Vernon Bailey, at an earlier time saved some specimens from Elk River. The name _bangsi_ was proposed in recognition of the superior work done on American weasels by the late Outram Bangs.