Microtus hyperboreus Vinogradov, 1934 . Trav. L'Inst. Zool. Acad. Sci., 1933:1.

TYPE LOCALITY: Siberia, Verhoiansk Mtns .

DISTRIBUTION: NE Siberia, basin of Yana River, Berhoiansk Range, and Taimyr Peninsula (see Ellerman and Morrison-Scott, 1951).

SYNONYMS: swerevi.

COMMENTS: Subgenus Alexandromys . Reviewed by Gromov and Polyakov (1977). Corbet (1978c) included hyperboreus in M. middendorffi because Gileva (1972) had demonstrated their complete interfertility. Pavlinov and Rossolimo (1987), however, recognized M. hyperboreus, noting that the two are clearly morphologically distinct and that material in published studies probably omitted true hyperboreus . Meier (1983) recognized the two species as closely related and noted that no study of variability within middendorffi had been made, and more importantly, that insufficient material from the type locality had been analyzed. Vorontsov and Lyapunova (1976) considered M. hyperboreus and M. middendorffi to be chromosomally closely related to North American M. miurus .