When Swarth (_loc. cit._) named the red-backed mouse of the mainland of southern Alaska as a new subspecies, he characterized it as "Size rather large. Differs from _E._ [= _Clethrionomys_] _wrangeli_, nearest it geographically, in cranial characters and in much longer tail; from _E. caurinus_, the species to the southward in British Columbia, in larger size and longer tail." He remarked (_loc. cit._): "I had supposed that the red-backed mouse occurring on the mainland coast of this region would prove to be _E. wrangeli_, but the latter appears to be purely an insular species. I have had no specimens of that race for comparison, but the _Evotomys_ secured differ so widely from it in all the essential peculiarities of the species as given in the published descriptions that there seems little doubt of their belonging to a different species. _Wrangeli_ has a short tail, less than twice as long as the hind foot--in adults of _phaeus_ the tail is invariably more than twice the length of the foot, frequently more than a third of the entire length of the animal." The external and cranial measurements of two subadults in the United States National Museum (No. 217413 from Quadra Lake and No. 217415 from Marten Arm, Boca de Quadra, taken in mid-February) and three old adults from Fort [= Port] Simpson, British Columbia (Nos. 90263-90264, 90272 USBS), are almost the same as those given by Swarth in the original description of _Clethrionomys phaeus_. In cranial measurements, as well as in the structure of the palate and last upper molar, _C. phaeus_ agrees with the _gapperi_ group (to which it has been assigned by Davis, The Recent Mammals of Idaho, The Caxton Printers, p. 306, April 5, 1939, and by Orr, Jour. Mamm., 26:69, February 12, 1945) and differs from _Clethrionomys occidentalis caurinus_ (which was assigned above to the _occidentalis_ group, formerly the _californicus_ group). Since the measurements of specimens examined by us, as well as those recorded by Swarth (_op. cit._), fall within the range of those of the species _Clethrionomys gapperi_, and since the differences between _phaeus_ and _C. g. saturatus_ are of the kind and degree that separate subspecies in _C. gapperi_ we employ the name combination _Clethrionomys gapperi phaeus_ (Swarth). _C. g. saturatus_, as understood by us, occurs to the southeast of _C. g. phaeus_ in the Rocky Mountains of British Columbia, and in northeastern Washington, northern Idaho and northwestern Montana. _Specimens examined._--Total, 23, distributed as follows: Alaska: Chickamin River (Behm Canal), 15 (MVZ); Boca de Quadra, 3 (MVZ); Marten Arm, Boca de Quadra, 1 (USNM); Quadra Lake, 1 (USNM). British Columbia: Fort [= Port] Simpson, 3 (USBS). Clethrionomys gapperi wrangeli (Bailey) 1897. _Evotomys wrangeli_ Bailey, Proc. Biol. Soc. Washington, 11:120, May 13, type from Wrangell, Wrangell Island, Alaska.