ity 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.

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 wit