Produced by Chris Curnow, Joseph Cooper and the Online Distributed Proofreading Team at http://www.pgdp.net UNIVERSITY OF KANSAS PUBLICATIONS MUSEUM OF NATURAL HISTORY Volume 9, No. 4, pp. 85-104, 2 figs. in text May 10, 1956 Subspeciation in the Meadow Mouse, Microtus pennsylvanicus, in Wyoming, Colorado, and Adjacent Areas BY SYDNEY ANDERSON UNIVERSITY OF KANSAS LAWRENCE 1956 UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY Editors: E. Raymond Hall, Chairman, A. Byron Leonard, Robert W. Wilson Volume 9, No. 4, pp. 85-104, 2 figures in text Published May 10, 1956 UNIVERSITY OF KANSAS Lawrence, Kansas PRINTED BY FRED VOILAND, JR., STATE PRINTER TOPEKA, KANSAS 1956 Subspeciation in the Meadow Mouse, Microtus pennsylvanicus, in Wyoming, Colorado, and Adjacent Areas BY SYDNEY ANDERSON INTRODUCTION In the region including Wyoming and Colorado, _Microtus pennsylvanicus_ has been divided into two subspecies: the pale _M. p. insperatus_ (J. A. Allen) inhabits the Black Hills of the northeasternmost part of Wyoming; the dark _M. p. modestus_ (Baird) inhabits extensive areas in both Wyoming and Colorado. Initial examination of _Microtus pennsylvanicus_ revealed that specimens from the Big Horn Mountains of north-central Wyoming (within the range of _modestus_ as mapped by Hall and Cockrum 1952:407), in color at least, resemble the subspecies _insperatus_ more than they do _modestus_, and that specimens from southwestern Wyoming are notably dark. Durrant (1952:363) noted that specimens from Utah are dark, and Davis (1939:315) did the same for specimens from near Pocatello, Idaho. It seemed, therefore, that dark color might characterize populations of a wide geographic region and distinguish them from _modestus_ named from southern Colorado. Also, there seemed to be a hiatus of at least 180 miles between the ranges of _modestus_ in northern Colorado and _modestus_ in eastern Wyoming, and an even greater distance separating populations of _modestus_ in northern Colorado from those in western Wyoming. _Microtus pennsylvanicus_ has not been taken in central or southeastern Wyoming despite extensive collecting there, which yielded numerous records of other kinds of _Microtus_ (_M. longicaudus_, _M. montanus_, and _M. ochrogaster_). Subsequent study revealed a pattern of geographic variation within the range now ascribed to _modestus_ which, in my opinion, can be described best by the recognition of three new subspecies. MATERIALS, METHODS, AND ACKNOWLEDGMENTS