_Remarks._--As early as 1858 (p. 159) Baird recognized an individual of this race from Pembina, Minnesota, as pertaining to a distinct species. Although he used for it the specific name _pusillus_ originally proposed by DeKay for a small weasel from the state of New York, Baird wisely noted that the specimen he described "may be different from the New York species. . . ." After preparing this account, Baird included a second specimen, from Fort Steilacoom, Washington Territory, which he thought might be the same, but the differences that he was careful to point out, in the light of later knowledge, show it to be of the species _Mustela erminea_. Only a few other naturalists followed Baird in distinguishing the least weasel as a separate species until Bangs in 1896 (p. 21) clearly differentiated it and proposed for it the name _Putorius rixosus_, which continues in use today and applies to the species. The accumulation at the National Museum of Canada, through the energy of Dr. R. M. Anderson, of a good series of specimens from Saskatchewan in the general vicinity of the type locality allows for the first time an adequate conception of the amount of secondary sexual variation and individual variation and permits recognition of subspecific characters to differentiate between _M. r. rixosa_ and the subspecies _eskimo_ and _campestris_. In comparison with the subspecies _allegheniensis_ the basis for segregation is less clear and will remain somewhat in doubt until additional adults of _allegheniensis_ from, say, Pennsylvania, become available with accurate external measurements taken in the flesh and especially with complete skulls. Intergradation with the subspecies _eskimo_ is suggested by the short tail of the specimen from fifteen miles east of Atlin, British Columbia; in other particulars that specimen, a skin-alone, agrees with the subspecies _rixosa_. Intergradation with _campestris_ is indicated by increased size of some specimens from North Dakota, and is suggested with _allegheniensis_ by the color of specimens from Wisconsin and Illinois. Three specimens from Winona County, in southeastern Minnesota, unfortunately are skulls-alone without external measurements. Also, two of these skulls are of young animals. The one adult, unsexed, is from Crystal Springs. Selected cranial measurements are: basilar length, 28.5; length of tympanic bulla, 10.9. These measurements accord with those of males of the subspecies _rixosa_ to which the specimens from Winona County, therefore, are here assigned. The possibilities have not been excluded, however, that the adult is an unusually large female of the subspecies _campestris_ or a male of _allegheniensis_ that has tympanic bullae longer than average for that subspecies.