1898. _Evotomys caurinus_ Bailey, Proc. Biol. Soc. Washington,
12:21, January 27, type from Lund, east shore Malaspina Inlet,
British Columbia.
1935. _Clethrionomys gapperi caurinus_, Racey and Cowan, Rept.
British Columbia Prov. Mus. for 1935, p. H 25.
Prior to 1935 _caurinus_ was considered to be a monotypic species. In
1935 Racey and Cowan (Rept. British Columbia Provincial Museum for
1935, pp. H 25-H 26) examined material from southwestern British
Columbia of _C. caurinus_, including a series of 24 specimens from Alta
Lake, and compared it with _Clethrionomys gapperi occidentalis_ and
_C. g. saturatus_. They found _caurinus_ to be distinct from _C. g.
saturatus_ but were "not convinced that _occidentalis_ and _caurinus_
both merit systematic recognition; should they prove to be
indistinguishable, as the little available material indicates,
_occidentalis_ will take precedence on grounds of priority. It is our
opinion that further study of the distribution of the genus in British
Columbia will lead to the recognition of _occidentalis_ as the form
inhabiting coast-line and _saturatus_ the interior of British Columbia"
p. H 26. In the face of these opinions Racey and Cowan nevertheless
recognized _caurinus_ under the name _Clethrionomys gapperi caurinus_
(Bailey).
In spite of the treatment by Racey and Cowan (_op. cit._) of
_occidentalis_ and _caurinus_ as subspecies of _C. gapperi_, later
authors arranged _occidentalis_ as a member of the "_californicus_"
group although they retained _caurinus_ in the _gapperi_ group. For
example, Davis (The Recent Mammals of Idaho, The Caxton Printers, pp.
307-308, 1939) assigned _C. caurinus_ to the _gapperi_ group, although
he regarded _C. caurinus_ as a species (not a subspecies). He regarded
also _C. occidentalis_ as a species (not a subspecies) but assigned
it to the _californicus_ group. Dalquest (Univ. Kansas Publ., Mus.
Nat. Hist., 2:344, April 9, 1948) considered _occidentalis_ to be
conspecific with _Clethrionomys californicus_ and wrote (_op.
cit._:101): "The _californicus_ group, I feel, contains only the races
of _Clethrionomys californicus_, while the _gapperi_ group contains _C.
gapperi_ and its races, including _caurinus_, and possible other
species." Dalquest gave no indication that he had examined any
specimens of _caurinus_.
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.