When Dalquest (_op. cit._:344) arranged _occidentalis_ and _californicus_ as subspecies of the same species, he used the name combination _Clethrionomys californicus occidentalis_ because he ignored, or was unaware of, the page priority of _occidentalis_ over _californicus_. We regard the anterior position of _occidentalis_ as nomenclatural priority and therefore employ _occidentalis_ rather than _californicus_ as the specific name. Differences between the _gapperi_ group and the _occidentalis_ group include: postpalatal bridge (complete in both groups) truncate posteriorly in the _gapperi_ group and with a median, posteriorly directed, spine in the _occidentalis_ group (this character is not evident in all specimens; some _gapperi_ have a spine, and some _occidentalis_ have the spine much reduced); dentition of the _occidentalis_ group is heavier; enamel pattern of M3 and m1 in _occidentalis_ more simplified--the number of salient and re-entrant angles tends to be reduced in adults of the _occidentalis_ group. An examination of specimens of _caurinus_ (British Columbia: Mt. Seymour, 2 KU; Lund, Malaspina Inlet, 2 USBS; and Inverness, mouth Skeena River, 1 USBS), reveals that, in the presence of the median postpalatal spine and in the characters of the molars, _caurinus_ agrees with the _occidentalis_ group. Clethrionomys occidentalis nivarius (Bailey) 1897. _Evotomys nivarius_ Bailey, Proc. Biol. Soc. Washington, 11:136, May 13, type from northwest slope of Mount Ellinor, 4000 ft., Olympic Mts., Mason County, Washington.