ARBOREAL RICE RATS — HERSHKOVITZ 515 



with mesostyle (id) as a functional unit; procingulum of upper molars 

 and postcingulum of lower molars present and usually well developed. 

 Remarks: With few exceptions, all real species of oryzomyine 

 rodents are well defined. Unfortunately, the multiplication of names 

 has made the identification of any one of them an extremely arduous, 

 sometimes nearly impossible, task. A total of 54 names, mostly of 

 specific grade, have been given to representatives of Oecomys alone. 

 These are shown to be applicable to only two species with a com- 

 bined total of nine subspecies. 



Subgenus Orysomys (Oecomys) Thomas 



QScomys, Thomas, Ann. Mag. Nat. Hist., ser. 7, vol. 18, p. 444, 1906 (subgenus of 

 Oryzomys Baird); ser. 8, vol. 3, pp. 378-379, 1909 (genus). 



Oecomys, Gyldenstolpe, Kungl. Svenska Vet.-Akad. Handl., ser. 3, vol. 11, p. 38, 

 1932 (characters; list of species). — Tate, Amer. Mus. Nov., No. 581, 

 p. 10, 1932 (taxonomic history). — Ellerman, The families and genera of living 

 rodents, vol. 2, pp. 340, 342, 357, 408, 1941 (subgenus of Oryzomys). 



Oryzomys, Goldman, North American Fauna, No. 43, pp. 15, 82, 1918 (part, 

 Oryzomys iecius group). 



Type species: Rhzpidomys henevolens Thomas [=Oryzomys 

 (Oecomys) bicolor phaeotis Thomas], by original designation. 



Included species: Oryzomys concolor Wagner, 0. bicolor Tomes. 



Distribution (figs. 1, 2): Forested parts of the tropical and 

 subtropical zones of Central and South America, from Costa Rica 

 through Panama into Colombia, Ecuador, Peru, Bolivia, Venezuela, 

 Trinidad, the Guianas and Brazil; altitudinal range from near sea 

 level to approximately 2,000 meters above. 



The ranges of the two species are coextensive in Panama, the Rfo 

 Orinoco basin of Colombia and Venezuela, and the Amazonian region. 

 So far as known, only the larger species, Oryzomys concolor, occurs in 

 Costa Rica, northern Colombia, northwestern Venezuela, and Trini- 

 dad. The smaller 0. bicolor occurs alone in western Ecuador. 



Taxonomic Histort 



The first name proposed for an arboreal rice rat is Mus cinnamo- 

 meus Pictet and Pictet, 1844. It is based on an eastern Brazilian 

 representative of the larger species of subgenus Oecomys. Unfortu- 

 nately, it is invalid because the name Mus cinnamomeus had already 

 been used by Lichtenstein in 1830 for a species of spiny rats of the 

 modern genus Proechimys. The next name for an Oecomys is Hesper- 

 omys concolor Wagner, 1845. It was given to the large form discovered 

 by Johann Natterer in the forests of the upper Rio Negro, northwestern 

 Brazil. While the name concolor was virtually ignored by recent 

 authors, the animal it represents has since been redescribed under 

 27 different names. 



