1899. =oribasus= (_Putorius (Arctogale) longicauda_) Bangs [= _Mustela frenata oribasus_], Proc. New England Zoöl. Club, 1:81, December 27, 1899, applies to the long-tailed weasel of the Rocky Mountains northward from Yellowstone National Park. 1900. =eskimo= (_Putorius rixosus_) Stone [= _Mustela rixosa eskimo_], Proc. Acad. Nat. Sci. Philadelphia, 1900:44, March 24, 1900, is applied to the least weasel of Alaska and adjacent parts of boreal North America. 1901. =allegheniensis= (_Putorius_) Rhoads [= _Mustela rixosa allegheniensis_], Proc. Acad. Nat. Sci. Philadelphia, 1900:75, March 25, 1901, applies to the least weasel of the eastern United States. 1902. =perdus= (_Putorius tropicalis_) Merriam [= _Mustela frenata perda_], Proc. Biol. Soc. Washington, 15:67, March 22, 1902, applies to the long-tailed weasel of the Lower Tropical Life-zone from southern Veracruz into Guatemala. 1903. =microtis= (_Putorius_) Allen [= _Mustela erminea richardsonii_], Bull. Amer. Mus. Nat. Hist., 19:563, October 10, 1903, is a name applied to an individual ermine of small size from Shesley, British Columbia, which Allen thought was specifically distinct from the ermine of the Hudsonian Life-zone and adjacent territory. Now the name is arranged as a synonym of _richardsonii_. 1904. =audax= (_Putorius_) Barrett-Hamilton [= _Mustela erminea arctica_], Ann. and Mag. Nat. Hist., ser. 7, 13:392, May, 1904. In the original description the type locality, Discovery Bay, was erroneously stated to be in Greenland and the name _audax_ until 1945 was applied to the kind of weasel occurring in northern Greenland whereas the type specimen was taken instead in northern Ellesmere Island and because the weasel there is subspecifically indistinguishable from ermines from farther west, _audax_ is a synonym of _Putorius arcticus_. 1904. =imperii= (_Putorius arcticus_) Barrett-Hamilton [= _Mustela erminea richardsonii_], Ann. and Mag. Nat. Hist., ser. 7, 13:392, May, 1904, based on an animal from Fort Simpson, Mackenzie, Canada, proves to be inseparable from _richardsonii_ which has priority. 1904. =polaris= (_Putorius arcticus_) Barrett-Hamilton [= _Mustela erminea polaris_], Ann. and Mag. Nat. Hist., ser. 7, 13:393, May, 1904, is the name used for the ermine of eastern Greenland and since 1945 has been used for the weasel of Greenland as a whole. 1905. =macrophonius= (_Putorius_) Elliott [= _Mustela frenata macrophonius_], Proc. Biol. Soc. Washington, 18:235, December 9, 1905, applies to the long-tailed weasel of the mountains along the eastern border of Veracruz.