Synaptomys Baird, 1858 . Mammalia in Repts. U.S. Expl. Surv., 8(1):558.

TYPE SPECIES: Synaptomys cooperi Baird, 1858 .

SYNONYMS: Mictomys, Plioctomys .

COMMENTS: Many taxonomic characters link Synaptomys with the true lemmings ( Lemmus and Myopus) in a clade, usually treated as the tribe Lemmini, believed to represent an early line of arvicoline evolution (Carleton, 1981; Chaline and Graf, 1988; Graf, 1982; Gromov and Polyakov, 1977; Hinton, 1926; Hooper and Hart, 1962; Koenigswald, 1980). Fossil history reviewed by Koenigswald and Martin (1984). Although described as a genus, Miller (1896) arranged Mictomys as a subgenus of Synaptomys, as conventionally recognized (Hall, 1981; Howell, 1927). Paleontologists, however, have emphasized the dental divergence of Synaptomys and Mictomys at the generic level (Koenigswald and Martin, 1984; Repenning and Grady, 1988), although both are presumed to have separated from a common ancestor ( Plioctomys) in the late Pliocene. Current specific and subspecific classification essentially derives from Howell (1927).