1897. _Microtus canicaudus_ Miller, Proc. Biol. Soc. Washington,
11:67, April 21, type from McCoy, Willamette Valley, Polk County,
Oregon.
In 1938 when one of us (Hall, Proc. Biol. Soc. Washington, 51:131-134,
August 23, 1938) arranged several nominal species of _Microtus_ as
subspecies of the species _Microtus montanus_, _Microtus canicaudus_ was
not included because that writer had not examined representative
specimens. In the U.S. Biological Surveys collection in the U.S.
National Museum we have examined specimens of _M. m. canicaudus_, all
from Oregon, as follows: Hood River (Catalogue Nos. 262583-262586);
Canby (262577, 262578); Wapinitia (79985-79988); Sheridan (69779,
69780); McCoy (75834-75842, 77744); Salem (246736); Albany (161554); and
Corvallis (242552). The four specimens from Wapinitia seem to be those
that Bailey (N. Amer. Fauna, 17:29, June 6, 1900) listed as _Microtus
montanus_. The diagnostic characters mentioned by Miller in the
original description (Proc. Biol. Soc. Washington, 11:67, April 21,
1897) included the following: size approximately the same as in
_Microtus [montanus] nanus_; upper parts yellowish; tail usually nearly
uniform grayish above and below; auditory bullae much inflated; lateral
pits at posterior edge of bony palate unusually shallow. Because the
tails of the original series were understuffed and variously rotated,
they seemed to be less sharply bicolored than is the case, as shown by
subsequently collected specimens. Otherwise we find that the characters
mentioned above differentiate _canicaudus_ from its nearest relatives,
_Microtus montanus canescens_ to the northward, _M. m. nanus_ to the
eastward, and _M. m. montanus_ to the southward. In _canicaudus_ we have
noted one additional differential character; the interpterygoid space is
acuminate anteriorly. In this feature and in each of the other features
mentioned above, intergradation with _Microtus montanus nanus_ is seen
in the specimens from Hood River and Wapinitia. In the specimens from
Hood River the auditory bullae are only slightly less inflated than in
those topotypes of _canicaudus_ having the smallest bullae; there is
appreciable variation in size of the bullae in the topotypes. Even so,
the minimum size of bullae among the topotypes is larger than the
maximum size in the specimens from Wapinitia. The four specimens from
Wapinitia have the yellowish color of _canicaudus_ to a considerable
degree, and show intergradation between _canicaudus_ and _nanus_ in
depth of the palatal pits and shape of interpterygoid space. The
slightly larger size of these specimens from Wapinitia suggests
intergradation with _M. m. montanus_. The tympanic bullae in the
specimens from Wapinitia seem to be smaller than in specimens of
_canicaudus_, _nanus_, or _montanus_.
Because of the intergradation described above between _Microtus montanus
nanus_ and _M. canicaudus_, the latter should stand as _Microtus
montanus canicaudus_.
* * * * *
Bailey (N. Amer. Fauna, 55:206, August 29, 1936) recorded _canicaudus_
from Warm Springs in the Deschutes Valley of Oregon and from the state
of Washington. Other authors also have recorded _canicaudus_ from the
state of Washington. Our examination of specimens leads us to conclude,
as did Dalquest (Univ. Kansas Publ., Mus. Nat. Hist., 2:348, 349, April
9, 1948), that _canicaudus_ does not occur in Washington. The reported
occurrence of _M. canicaudus_ at Warm Springs, Deschutes Valley, Oregon,
seems to be the result of an error in identification. The specimens
concerned seem to be two _Microtus longicaudus mordax_ (Nos. 207060 and
207082 U.S.N.M.). They are labeled as collected at "Warm Springs (Mill
Cr.--20 Mi. W of)". Bailey's (_op. cit._, fig. 46, p. 209) map showing
the distribution in Oregon of _Microtus mordax mordax_ [=_Microtus
longicaudus mordax_] has a locality-dot at Warm Springs itself. Bailey
seems to have erred; he should have placed this dot 20 miles farther
west, we think. When preparing his map (_op. cit._, fig. 43, p. 205)
showing the geographic distribution of _Microtus canicaudus_, Bailey
seems to have misidentified these same two specimens as _M. canicaudus_,
and for them placed a locality-dot on his map 20 miles east (instead of
west) of Warm Springs. In brief, Bailey probably did not see any
specimens of _canicaudus_ or specimens of any other subspecies of
_Microtus montanus_ from Warm Springs.
_Transmitted February 15, 1951._
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