ARBOREAL RICE RATS — HERSHKOVITZ 547 



[Oryzomys] vicencianus, Tate, Bull. Amer. Mus. Nat. Hist., vol. 7G, p. 190, 1939 

 ("juv. and synonym of helvolus"). 



(Ecomys mincae J. A. Allen, Bull. Amer. Mus. Nat. Hist., vol. 32, p. 603, 1913 

 (type locality, Minca, Santa Marta region, Magdalena, Colombia). — Good- 

 win, Bull. Amer. Mus. Nat. Hist., vol. 102, p. 301, 1953 (type history). 



(Ecomys caicarae J. A. Allen, Bull. Amer. Mus. Nat. Hist., vol. 32, p. 603, 1913 

 (type locality, Caicara, Rio Orinoco, Bolivar, Venezuela). 



Oecomys caicarae, Goodwin, Bull. Amer. Mus. Nat. Hist., vol. 102, p. 300, 1953 

 (type history and measurements). 



Oecomys guianae caicarae, Tate, Bull. Amer. Mus. Nat. Hist., vol. 76, p. 193, 1939 

 (Venezuela: Mt. Duida; Casiquiare). 



Oryzomys irinitatis, Tate (not Allen and Chapman), Bull. Amer. Mus. Nat. Hist., 

 vol. 76, p. 190, 1939 (part; Venezuela: Aguita; Mt. Duida). 



Type: Presumably in the Vienna Natural History Museum'; col- 

 lected Aug. 4, 1831, by Johann Natterer; original number, 174. 



Type locality: Eio Curicuriari, an affluent of the upper Rio 

 Negro, entering from the right below Sao Gabriel, Amazonas, Brazil. 



Distribution: Tropical and subtropical forested zones of Costa 

 Rica, Panama, northwestern Colombia, and eastern Colombia in 

 the Rio Orinoco drainage system, western and southern Venezuela in 

 the Lake Maracaibo and the middle and upper Rio Orinoco basins, 

 the Amazonian rain forest of Brazil and their extensions into extreme 

 northern Bolivia, eastern Peru, and eastern Ecuador; altitudinal 

 range, sea level to approximately 2,000 meters above. 



Characters: Generally brightly colored, upperparts ochraceous 

 buff to tawny finely ticked with dark brown, chest and belly white to 

 buff, throat and chin white. 



Measurements: See table 7. 



Variation: Two specimens from the type region are at hand. 

 One, from Jauarate, Rio Uaupes, above the type locality, is larger 

 than the type, its belly with a light buffy wash. The other, from 

 Yauanari, Rio Negro, below the type locality, is smaller, with belly, 

 chest, and sides ochi-aceous buff'. Underparts of the type are sharply 

 defined white. The same range of variation in color of underparts 

 obtains in most populations of the species. 



The type of Oecomys tapajinus Thomas and two other specimens 

 from Tauary, in the type region on the Rio Tapajoz, Brazil, do not 

 differ from concolor of the Rio Negro-Rio Orinoco basin. The under- 

 parts of one of the two Tauary specimens is creamy, most notably on 

 chest, throat, and chin ; in the other, the sam.e parts are sharply defined 

 white. A specimen from Lago Cuiteua, on the opposite side of the 

 Solimoes, is practically identical. A young individual from the Boca 

 do Igarape Piaba, also on the north bank of the Solimoes, shows the 

 old pelage being replaced by a more saturate new pelage. 



The type of marmosurus Thomas, from the middle Rio Orinoco, 

 Colombia, is not significantly different from any other individual of 



