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
[Pg 74]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
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 Microtusmontanus in the Bitterroot Valley of Montana, that did not fit thedescription of any named subspecies. These were laid aside until wecould examine the additional specimens from Montana in the BiologicalSurveys collection in the United States National Museum, some of whichpreviously had been reported by Bailey (N. Amer. Fauna, 17:31, June 6,1900) under the name Microtus nanus canescens Bailey [=Microtusmontanus canescens]. Our examination reveals that the animals from theBitterroot and Flathead valleys belong to an heretofore unrecognizedsubspecies 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; originalnumber 477.
Geographic distribution.—Flathead and Bitterroot valleys ofwestern 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 notquite to tips of premaxillary tongues; nasals usually truncateposteriorly, but rounded in some individuals; premaxillary tonguesterminating posteriorly in a short medial spine; zygomatic archeslightly constructed and usually more widely spreading posteriorlythan anteriorly; interparietal comparatively long and terminatingin a small, but distinct, medial spine, otherwise approximatelyrectangular in shape; exposed parts of upper incisors short and,for the species, only slightly procumbent; molar dentition weakand, in most specimens, especially so posteriorly; tympanic bullaelarge and well inflated, especially ventrolaterally; basioccipitalnarrow owing to the encroachment of the tympanic bullae.
Comparison.—Among named forms, Microtus montanus pratincolusmost closely resembles Microtus montanus nanus. The geographicrange of M. m. nanus adjoins that of M. m. pratincolus on threesides; there is no conspecific[Pg 76] subspecies adjoining the range ofM. m. pratincolus on the north. From M. m. nanus, M. m.pratincolus differs as fo