Female: Twelve adults and subadults from Maine and the area south to central Pennsylvania, yield average and extreme measurements as follows: Total length, 243 (225-260); length of tail, 63 (55-72); length of hind foot, 29.8 (26-32). Hamilton (1933:294) gives the weight of 15 adults from New York as 54 (45-71) grams. _Color._--As described in _Mustela erminea richardsonii_ except that underparts in summer Marguerite Yellow or even more whitish; least width of color of underparts averaging, in adult males from New York and Pennsylvania, 29 (27-32) per cent of greatest width of color of upper parts. Black tip of tail in same series averaging 42 (30-51) mm. which is 57 per cent of length of tail-vertebrae. _Skull._--Male (illustrated by 4 adults in table of cranial measurements, which see): See plates 2-4. As described in _Mustela erminea richardsonii_ except that: Weight, 1.5 (1.2-1.7) grams; basilar length, 35.7 (33.8-37.6). Female (illustrated by adult and subadults recorded in table of cranial measurements, which see): See plates 9-11. As described in _Mustela erminea richardsonii_ except that: Weight of 2 subadults, 0.92 (0.86-0.98) grams; basilar length, 32.4 (31.4-33.3). The skull of the male, in linear measurements, is approximately 13 (12-16) per cent smaller and 40 per cent lighter than in _M. e. richardsonii_. In relation to the basilar length, the skull averages slightly narrower, slightly shallower as measured in the vertical plane touching the posterior borders of the last upper molars, and the preorbital part is slightly longer. In skulls of females of _cicognanii_, linear measurements average 3 (0-6) per cent less, the weight is 16 per cent less and the teeth are 5 per cent shorter. In relation to the basilar length, measurements of the skull are approximately the same or slightly less in _cicognanii_. In comparison with _bangsi_, the male sex in linear measurements of the skull and teeth averages 11 per cent less than in _bangsi_ from Aitkin, Minn., and 6 per cent less than in _bangsi_ from Elk River, but in relation to the basilar length the preorbital region is larger. The weight is approximately a fourth less. In females the measurements average less, some being the same, and in relation to the basilar length, the bullae are shorter and the skull is shallower. The weight is about the same. _Remarks._--In January, 1838, in Charlesworth's Magazine of Natural History, C. L. Bonaparte proposed for three kinds of American weasels the names _Mustela cicognanii_, _Mustela richardsonii_ and _Mustela longicauda_.