Microtus oregoni (Bachman, 1839) . J. Acad. Nat. Sci. Philadelphia, 8:60.

TYPE LOCALITY: USA, Oregon, Clatsop Co., Astoria .

DISTRIBUTION: Moist coniferous forest seres of Pacific Northwest, from SW British Columbia, Canada, south to NW California, USA.

SYNONYMS: adocetus, bairdi, cantwelli, morosus, serpens .

COMMENTS: Subgenus Mynomes, sole member of oregoni species group sensu Zagorodnyuk (1990) . Type species of Chilotus, conventionally recognized as a subgenus of Microtus (see Anderson, 1959, 1960; Bailey, 1900), and occasionally including Old World M. socialis as a comember (Chaline, 1974; Ognev, 1964) or not (Anderson, 1959). Hooper and Hart (1962), however, found the morphological evidence insufficient to warrant subgeneric segregation of oregoni from North American species of Microtus, a viewpoint sustained by genetic distance comparisons (Moore and Janecek, 1990) and reflected in the classification of Zagorodnyuk (1990). Diploid number and sexdetermining mechanism unique among North American Microtus studied (Ohno et al., 1963). See Carraway and Verts, 1985 (Mammalian Species, 233).