Oecomys Thomas, 1906 . Ann. Mag. Nat. Hist., ser. 7, 18:444.

TYPE SPECIES: Rhipidomys benevolens Thomas, 1901 (= Hesperomys bicolor Tomes, 1860).

COMMENTS: Oryzomyine. Diagnosed as a subgenus of Oryzomys to segregate arboreal, pencil-tailed sigmodontines with a long palate from Rhipidomys, under which many of the species included here were first described. Thereafter treated alternatively as a subgenus of Oryzomys (Ellerman, 1941; Goldman, 1918) or as full genus (Gyldenstolpe, 1932; Thomas, 1917c) until Hershkovitz's (1960) revision stabilized its ranking as a subgenus (e.g., Cabrera, 1961; Hall, 1981). Systematists have recently acknowledged the morphological and karyotypic distinctiveness of Oecomys at the generic level (Carleton and Musser, 1984; Gardner and Patton, 1976; Reig, 1984, 1986), but this recognition as yet lacks convincing substantiation from a phylogenetic perspective.

Revised by Hershkovitz (1960), who consolidated some 25 species (e.g., Ellerman, 1941) into the two species bicolor and concolor . Although this gross underestimation of the species diversity within Oecomys has been intimated by other authors (e.g., Gardner and Patton, 1976; Reig, 1986), it has yet to be documented within a taxonomic revision. The species identified here issue from our revision in progress; we are confident that all of these will stand as valid yet some, such as O. trinitatis, are undoubtedly composites even now.