Microtus montanus (Peale, 1848) . Mammalia in Repts. U.S. Expl. Surv., 8:44.

TYPE LOCALITY: USA, California, Siskiyou Co., headwaters of Sacramento River, near Mount Shasta .

DISTRIBUTION: Cascade, Sierra Nevada, and Rocky Mountain ranges: SC British Columbia, Canada, south to EC California, S Utah, and NC New Mexico, USA; disjunct populations in S Nevada, EC Arizona, and NE New Mexico.

SYNONYMS: amosus, arizonensis, canescens, caryi, codiensis, dutcheri, fucosus, fusus, longirostris, micropus, nanus, nevadensis, nexus, pratincola, rivularis, undosus, yosemite, zygomaticus .

COMMENTS: Subgenus Mynomes, montanus species group sensu Zagorodnyuk (1990) . Geographic variation and subspecific classification assessed by Anderson (1959), who viewed M. oeconomus as its sister species. Hooper and Hart (1962) arranged M. montanus with M. pennsylvanicus and M. townsendii, a general relationship corroborated by karyotypic and genic analyses (Modi, 1987; Moore and Janecek, 1990). Two karyotypic morphs reported by Judd et al. (1980), who raised the question of their specific distinction.