Dicrostonyx Gloger, 1841 . Gemein Hand.- Hilfsbuch. Nat., 1:97.

TYPE SPECIES: Mus hudsonius Pallas, 1778 .

SYNONYMS: Borioikon, Cuniculus, Misothermus, Tylonyx.

COMMENTS: At first Dicrostonyx was grouped with other lemmings following Miller's (1896) classic Lemmi-Microti division (e.g., Ellerman, 1941; Hinton, 1926; Ognev, 19636; Simpson, 1945). An impressive variety of data, however, requires its tribal separation (Dicrostonychini) from the true lemmings ( Lemmini) and suggests that the origin of Dicrostonyx dates to the earliest radiation of arvicolines (Carleton, 1981; Chaline and Graf, 1988; Gromov and Polyakov, 1977; Hinton, 1926; Hooper and Hart, 1962; Kretzoi, 1969; Modi, 1987).

The simple viewpoint of a single circumpolar species, D. torquatus, as advanced by Ognev (1963b) and Rausch (1953, 19636), has been unsettled by karyotypic reports of the past two decades (Chernyavskii and Kozlovskii, 1980; Kröhne, 1982; Rausch, 1977; Rausch and Rausch, 1972). The occurrence of varying lemmings in quite different tundra biotopes (e.g., see Youngman, 1975) alone might have questioned the existence of only one species, but the karyological and breeding results of Rausch and Rausch (1972) first drew attention to the possibility of a superspecies complex among North American Dicrostonyx, an interpretation reiterated by Rausch (1977; see summary of chromosomal variation in Kröhne, 1982). Later authorities either listed the North American karyotypic morphs as species (Corbet and Hill, 1991; Honacki et al., 1982; Jones et al., 1986) or continued to recognize most as subspecies of D. groenlandicus, together with D. exsul on St. Lawrence Island and D. hudsonius on the Ungava Peninsula (Hall, 1981).

After examining museum specimens, we readily appreciate the specific distinctiveness of groenlandicus, hudsonius, richardsoni, and unalascensis. The morphological discrimination of others (kilangmiutak, nelsoni, and rubricatus) is more subtle but may yield to careful description and analysis; we have not seen examples of nunatakensis, an isolated taxon described as a subspecies of torquatus by Youngman (1967). Unfortunately, the provocative findings of Rausch and others have not been explored and substantiated using other taxonomic information; in this regard, Youngman's (1975) narrative overview of species and racial distributions warrants attention in future efforts. We herein continue to list the species of Dicrostonyx as provisional and stress that their repetition in checklists like this enhances neither our confidence in the number of biological entities nor our understanding of their biogeographic significance.