Microtus xanthognathus (Leach, 1815) . Zool. Mise., 1:60.

TYPE LOCALITY: Canada, Manitoba, Hudson Bay .

DISTRIBUTION: Western boreal taiga zone: EC Alaska to W Northwest Territories, southeastwards to C Alberta and western coast of Hudson Bay, Canada.

COMMENTS: Relationships obscure: probably not a sister species to M. chrotorrhinus as once believed (see that account and Lidicker and Yang, 1986); placed by Zagorodnyuk (1990) in the subgenus Aulacomys, richardsoni species group. Karyotype reported and affinities discussed by Rausch and Rausch (1974).