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.