Onychomys Baird, 1858 . Mammalia in Repts. U.S. Expl. Surv., 8(1):458.

TYPE SPECIES: Hypudaeus leucogaster Wied-Neuwied, 1841 .

COMMENTS: Peromyscine. Revised by Hollister (1914). Chromosomal evolution among three species investigated by Baker et al. (1979), allozymic differentiation by Sullivan et al. (1986), and mitochondrial-DNA phylogeny by Riddle and Honeycutt (1990); historical biogeography interpreted by Riddle and Honeycutt (1990); affinity of Recent and fossil forms evaluated by Carleton and Eshelman (1979). Phyletic affinity to other sigmodontine genera assessed by Carleton (1980), Hooper and Musser (1964b), and Stangl and Baker (1984b).