_Remarks._--Animals from the Black Hills of South Dakota and Wyoming are thought of as most characteristic of this geographic race. Intergradation is noted with _Zapus hudsonius pallidus_ and is discussed in the account of that subspecies. _Specimens examined._--Total, 66, distributed as follows: MONTANA: _Big Horn County_: Rotten Grass Creek, north base Big Horn Mts., 2 (USBS); _Little Big Horn River, 2 mi. from Wyoming line_, 1 (USBS). SOUTH DAKOTA: _Custer County_: _Custer_, 3 (USNM); Bull Springs, 6 (Clev. MNH); _Beaver Creek, Wind Cave Nat'l Park_, 1 (UM); Wind Cave Nat'l Park Game Ranch, Cold Spring Creek, Wind Cave Nat'l Park, 2 (UM); _Pennington County_: _Rapid Creek, 2 mi. W Pactola, 4800 ft._, 3 (UM); Castle Creek, R. 2E, T. 1N, 6500 ft., 3 (UM); Nelsons Place, 3 mi. SE Hill City, 6 (UM); _Palmer Gulch, 4 mi. SE Hill City_, 3 (UM); _Palmer Gulch_, 9 (FM); _no definite locality_, 4 (UM). WYOMING: _Crook County_: Devils Tower, flood plain Belle Fourche River, 3350 ft., 1 (USBS); Bear Lodge Mts., 4 (USBS); _15 mi. N Sundance, Black Hills Nat'l Forest, 5500 ft._, 2; _3 mi. NW Sundance, 5900 ft._, 17; _Sundance_, 2 (USBS). _Weston Co._: 1-1/2 mi. E Buckhorn, 6150 ft., 5. _Marginal records._--Montana: Rotten Grass Creek, N base Big Horn Mts. South Dakota: Nelsons Place, 3 mi. SE Hill City; Wind Cave Nat'l Park Game Ranch, Cold Spring Creek. Wyoming: 1-1/2 mi. E Buckhorn, 6150 ft. =Zapus hudsonius canadensis= (Davies) _Dipus canadensis_ Davies, Trans. Linn. Soc. London, 4:157, 1798. _Zapus hudsonius hudsonius_, Preble, N. Amer. Fauna, 15:17, August 8, 1899 (part--the part from Ontario). _Zapus hudsonius canadensis_, Batchelder, Proc. New England Zool. Club, 1:5, February 8, 1899 (part--the part from Quebec); Anderson, Rept. Provancher Soc. Nat. Hist., Quebec, 1941:35-37, July 14, 1942 (part--the part from Quebec excepting the Gaspé Peninsula). _Zapus hudsonius ontarioensis_ Anderson, Ann. Rept. Provancher Soc. Nat. Hist., Quebec, 1942:59, September 7, 1943, type from Pancake Bay (Batchawana Bay) southeast end of Lake Superior, Algoma District, about 40 miles northeast of Sault Ste-Marie, Ontario. _Type._--No type specimen designated, subspecies characterized on the basis of two specimens obtained by Major General Thomas Davies within a few miles of the city of Quebec. _Range._--Eastern Ontario and western Quebec from Hudson Bay southward to the Great Lakes and into northwestern New York. See fig. 47. Zonal range: Transition and Canadian.