_Diagnosis._--Size small to medium; lambdoidal crest barely discernible; supraorbital notches even with, or posterior to, posterior notch of zygomatic plate; baculum with distinct keel on dorsal surface of tip which curves upward; pelage silky; ears long and pointed. _Geographic range._--Western Nearctic. West to Pacific Coast. South to Lat. 20°30' in Baja California and to northwestern Durango and southeastern Coahuila, Mexico. East to eastern New Mexico, westernmost Oklahoma, eastern Colorado, Wyoming, northwestern Nebraska, western and northwestern South Dakota, western and northwestern North Dakota, northeastern Minnesota, northern Wisconsin and Upper Peninsula of Michigan, and eastern Ontario. North to southwestern shore of Hudson Bay, southern shore of Great Slave Lake and Yukon River, Yukon. Genus #Tamias# Illiger _Tamias_ Illiger, J. K. W., Prodromus Syst. Mam. Avium, pp. 83, 1811. Type, _Sciurus striatus_ Linnaeus. _Tamias_, Howell, A. H., N. Amer. Fauna, 52:26, November 30, 1929. _Tamias_, Ellerman, J. R., The families and genera of living rodents. British Mus. (Nat. Hist.), 1:426, June 8, 1940. _Tamias_, Bryant, M. D., Amer. Midland Nat. 33:372, March, 1945. _Diagnosis._--Skull lightly built, narrow; postorbital process small and weak; lacrimal not elongated; infraorbital foramen lacks canal, relatively larger than in most sciurids; P3 absent; head of malleus elongated; plane of manubrium of malleus forms 60 degree angle with plane of lamina; hypohyal and ceratohyal bones of hyoid apparatus fused in adults; conjoining tendon of anterior and posterior digastric muscles rounded in cross section; keel on ventral surface of tip which curves upward in baculum; tail less than 38 per cent of total length; five longitudinal dark and four longitudinal light stripes present but two dorsal light stripes at least twice as broad as other stripes; four lateral dark stripes short. _Geographic range._--Eastern Nearctic. West to Turtle Mountains, North Dakota; eastern North Dakota, eastern South Dakota, Nebraska, Kansas, and Oklahoma. South to southern Louisiana, Mississippi, Alabama, northwestern Georgia. East to Atlantic Coast from South Carolina to Nova Scotia. North to northeastern Quebec and southern tip of Hudson Bay. DISCUSSION