_Remarks._--The earliest of the post-Linnaean references to this weasel mostly were under the specific name _erminea_ in the belief that the American animal was the same as the larger of the two common species of weasel in the Old World. The name _noveboracensis_, now in use for this subspecies, was applied in 1840 and since that time the males usually have borne that name; the females, because they are smaller, were more frequently confused with some other species. Audubon and Bachman in 1853 even proposed the name _agilis_ for the female in the mistaken belief that it was a species distinct from the male. After 1896, when Bangs correctly classified the weasels of the eastern United States, the males have been correctly identified and the females, except by a few authors, likewise have been correctly named. Because many early American naturalists did their first collecting of mammals in the geographic range of _noveboracensis_, the person who examines labels of specimens of this subspecies can find data written in the hand of Spencer Fullerton Baird, Theodore Roosevelt, and other naturalists famous for their work as scientists or accomplishments otherwise. The material is more nearly adequate than is that of many other subspecies and the number of specimens is exceeded--and only slightly--by that of the subspecies _nevadensis_, which like _noveboracensis_ has a relatively large geographic range. Intergradation with _Mustela frenata spadix_ is indicated by subadult males from western Wisconsin, namely, one from Gordon, three from Colfax and one from Meridean. Linear measurements of the teeth of these specimens are exactly intermediate between those of _spadix_ from Elk River, Minnesota, to the west, and _noveboracensis_ from, say, Beaver Dam, Wisconsin, to the east. The specimens from western Wisconsin show approach to spadix also in that the length of the tooth-rows and breadth of the rostrum are slightly greater than in _noveboracensis_ from farther east, say, Beaver Dam, Wisconsin. Indeed, animals from as far east as Beaver Dam itself might be thought of as showing some approach to _spadix_. Although, along the eastern seaboard, the upper lips, with rare exceptions, are the same color as the underparts, farther west, in Michigan and Wisconsin, the lips more often than not are white. Animals from Beaver Dam have slightly shorter black tips on the tails, broader extent of the light color of the underparts and females average slightly larger than typical _noveboracensis_, say, those from Massachusetts. Each of these differences reflects characters found better developed in the _spadix-longicauda_ stock to the west.