Microtus longicaudus (Merriam, 1888) . Am. Nat., 22:934.

TYPE LOCALITY: USA, South Dakota, Custer Co., Black Hills, Custer, 5500 ft .

DISTRIBUTION: Rocky Mountains and adjacent foothills, from E Alaska and N Yukon, south through British Columbia and SW Alberta, Canada, to E California and W Colorado; including Pacific coastal taiga to N California; disjunct southern pockets in S California, Arizona, and New Mexico, USA.

SYNONYMS: abditus, alticola, angusticeps, angustus, baileyi, bernardinus, cautus, coronarius, halli, incanus, latus, leucophaeus, littoralis, macrurus, mordax, sierrae, vellerosus .

COMMENTS: Sometimes viewed as a Nearctic member of Chionomys (Anderson, 1959), or allocated to subgenus Microtus (Chaline, 1974; Hall, 1981), or to subgenus Aulacomys (Zagorodnyuk, 1990) . Although strongly differentiated relative to other North American Microtus (e.g., Hooper and Hart, 1962; Modi, 1987; Moore and Janecek, 1990), the phyletic affinity of M. longicaudus lies with this complex and not Old World Chionomys (Chaline and Graf, 1988; Gromov and Polyakov, 1977; Zagorodnyuk, 1990). The extensive karyotypic variation reported (Judd and Cross, 1980) suggests the need for taxonomic revision. Jones et al. (1986) viewed coronarius as an insular derivative and subspecies of M. longicaudus. See Smolen and Keller (1987, Mammalian Species, 271).