Nyctomys Saussure, 1860 . Rev. Mag. Zool. Paris, ser. 2, 12:106.

TYPE SPECIES: Hesperomys sumichrasti Saussure, 1860 .

COMMENTS: Middle American endemic of enigmatic phyletic position. Placed with thomasomyine group of South American sigmodontines by Hershkovitz (1944, 1962); others have disputed the association with thomasomyines, instead suggesting distant kinship to neotomine-peromyscines or a cladistic origin prior to both North and South American sigmodontines (Arata, 1964; Carleton, 1980; Haiduk et al., 1988; Hooper and Musser, 1964a; Voss and Linzey, 1981).