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A New Subspecies of Microtus montanus from Montana and Comments on Microtus canicaudus Miller By: Keith R. Kelson |
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BY E. RAYMOND HALL and KEITH R. KELSON University of Kansas Publications
Museum of Natural History
Volume 5, No. 7, pp. 73 79
October 1, 1951 University of Kansas
LAWRENCE
1951
UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY Editors: E. Raymond Hall, Chairman, A. Byron Leonard,
Edward H. Taylor, Robert W. Wilson Volume 5, No. 7, pp. 73 79
October 1, 1951 UNIVERSITY OF KANSAS
Lawrence, Kansas PRINTED BY
FERD VOILAND, JR., STATE PRINTER
TOPEKA, KANSAS
1951 23 7438
A New Subspecies of Microtus montanus from Montana and Comments on
Microtus canicaudus Miller BY E. RAYMOND HALL AND KEITH R. KELSON
In 1949, for the Museum of Natural History of the University of Kansas,
Mr. John A. White collected two specimens of the species Microtus
montanus in the Bitterroot Valley of Montana, that did not fit the
description of any named subspecies. These were laid aside until we
could examine the additional specimens from Montana in the Biological
Surveys collection in the United States National Museum, some of which
previously had been reported by Bailey (N. Amer. Fauna, 17:31, June 6,
1900) under the name Microtus nanus canescens Bailey [= Microtus
montanus canescens ]. Our examination reveals that the animals from the
Bitterroot and Flathead valleys belong to an heretofore unrecognized
subspecies which is named and described below. Microtus montanus pratincolus new subspecies Type. Female, adult, skull and skin, No. 34004, Univ. Kansas,
Mus. Nat. Hist.; from 6 mi. E Hamilton, 3700 ft., Ravalli County,
Montana; obtained on August 14, 1949, by John A. White; original
number 477. Geographic distribution. Flathead and Bitterroot valleys of
western Montana. Diagnosis. Size small for the species (see measurements). Color:
Essentially as in Microtus montanus nanus . Skull: Small, slender,
and comparatively smooth; rostrum moderately depressed distally;
nasals moderately inflated distally and extending posteriorly not
quite to tips of premaxillary tongues; nasals usually truncate
posteriorly, but rounded in some individuals; premaxillary tongues
terminating posteriorly in a short medial spine; zygomatic arches
lightly constructed and usually more widely spreading posteriorly
than anteriorly; interparietal comparatively long and terminating
in a small, but distinct, medial spine, otherwise approximately
rectangular in shape; exposed parts of upper incisors short and,
for the species, only slightly procumbent; molar dentition weak
and, in most specimens, especially so posteriorly; tympanic bullae
large and well inflated, especially ventrolaterally; basioccipital
narrow owing to the encroachment of the tympanic bullae. Comparison. Among named forms, Microtus montanus pratincolus
most closely resembles Microtus montanus nanus . The geographic
range of M. m. nanus adjoins that of M. m. pratincolus on three
sides; there is no conspecific subspecies adjoining the range of
M. m. pratincolus on the north. From M. m. nanus , M. m.
pratincolus differs as follows (measurements are all of males,
those of M. m. nanus being of nine topotypes and near topotypes
from central Idaho): size smaller (149 mm. as opposed to 165), tail
shorter (37 as opposed to 39), hind foot shorter (19 as opposed to
20), upper molar series shorter (expressed as a percentage of
basilar length, 25.5 as opposed to 26.3), mastoidal region broader
(expressed as a percentage of basilar length, 48.6 as opposed to
46.7), braincase slightly more vaulted (depth of braincase
expressed as a percentage of basilar length, 31.3 as opposed to
30.4) and more inflated laterally; tympanic bullae more inflated,
this inflation being the most conspicuous difference between the
two subspecies... Continue reading book >>
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