The red-backed mouse of the Olympic Peninsula was originally accorded specific rank. Currently it stands in the literature as a subspecies of the wide-spread species _Clethrionomys gapperi_ because Dalquest (Univ. Kansas Publ. Mus. Nat. Hist., 2:343, April 9, 1948) used the name-combination _Clethrionomys gapperi nivarius_. Taylor and Shaw had earlier (Occas. Papers Charles R. Conner Mus., 2:23, 1929) indicated the same status by using the name _Evotomys gapperi nivarius_. Davis (The Recent Mammals of Idaho, The Caxton Printers, Caldwell, Idaho, p. 306, April 5, 1939), however, indicated that the affinities of _nivarius_ were with the _californicus_ [= _occidentalis_] group, although he treated _nivarius_ as a distinct species. We have examined two adult females (K. U. Nos. 10707 and 10708) of _nivarius_ from Reflection Lake, 3800 ft., Jefferson County, Washington, and on the basis of their thick, instead of thin, pterygoid processes concur with Davis that the affinities of _nivarius_ are with the named kinds of _Clethrionomys_ now arranged as subspecies of _Clethrionomys occidentalis_, rather than with the kinds now arranged as subspecies of _Clethrionomys gapperi_. Although we are aware that Dalquest (_op. cit._:101-102) did not find actual intergradation between _nivarius_ and _Clethrionomys occidentalis occidentalis_--a ten-mile gap separated their ranges--we prefer to use the name combination _Clethrionomys occidentalis nivarius_. In doing so we recognize that intergradation ultimately may be found between the two species _C. occidentalis_ and _C. gapperi_; in that event the name _gapperi_ will apply as the name of the species because it has priority over _occidentalis_. The following named kinds of _Clethrionomys_ are considered to be subspecies of _Clethrionomys occidentalis_: CLETHRIONOMYS OCCIDENTALS OCCIDENTALIS (Merriam). 1890. _Evotomys occidentalis_ Merriam, N. Amer. Fauna, 4:25, October 8, type from Aberdeen, Chehalis County, Washington. 1894. _Evotomys pygmaeus_ Rhoads, Proc. Acad. Nat. Sci. Philadelphia, p. 284, October 23, type from mouth of Nisqually River, Pierce County, Washington. 1929. _Evotomys gapperi occidentalis_, Taylor and Shaw, Occas. Papers Charles R. Conner Mus., Washington State College, 2:23. 1948. _Clethrionomys californicus occidentalis_, Dalquest, Univ. Kansas Publ., Mus. Nat. Hist., 2:344, April 9. CLETHRIONOMYS OCCIDENTALIS CALIFORNICUS (Merriam). 1890. _Evotomys californicus_ Merriam, N. Amer. Fauna, 4:26, October 8, type from Eureka, Humboldt County, California. CLETHRIONOMYS OCCIDENTALIS CAURINUS (Bailey). 1898. _Evotomys caurinus_ Bailey, Proc. Biol. Soc. Washington, 12:21, January 27, type from Lund, east shore of Malaspina Inlet, British Columbia.