554 PROCEEDINGS OF THE NATIONAL MUSEUM vol. no 



Distribution: Trinidad, the Guianas, and eastern Venezuela, 

 including the coast and delta and basin of the lower Rio Orinoco; 

 altitudinal range from sea level to about 1,500 meters above. 



Characters: Like concolor but darker throughout; upperparts 

 tawny finely ticked with dark brown; underparts gray, sometimes 

 whitish or buffy with the plumbeous basal portions of the hairs 

 showing through. 



Measurements: See table 8. 



Variation: Underparts vary from whitish to dark gray with or 

 without a light buffy wash. In ail specimens, however, the basal 

 portions of the hairs of belly and chest are plumbeous and show 

 through the surface. A pectoral streak is present in the two speci- 

 mens from Caura, Trinidad, and in the specimens from Quebrada 

 Seca and Neveri, Venezuela. 



Remarks: Of a series of four specimens collected in Prince's Town, 

 Trinidad, Allen and Chapman described one as Oryzomys speciosus 

 and the others as 0. trinitatis. The basal portions of the belly hairs 

 in the first are more nearly white than in the others. The authors 

 noted that "in size, proportions and coloration [speciosus] strongly 

 suggests Hesperomys concolor Wagner." Paradoxically, they failed 

 to recognize the same relationship to the specimen they named 

 trinitatis. 



Oryzomys palmarius J. A. Allen and Oryzomys fulviventer J. A. Allen 

 are likewise based on differently colored individuals of a small series 

 taken from Nov. 23 through Dec. 10, 1898, in Quebrada Seca, Sucre, 

 Venezuela. In the fu'st, the underparts are typically grayish white 

 with the dark basal color of the hairs showing through. In the second, 

 the belly is buffy, the throat whitish. 



When Thomas erected the subgenus Oecomys in 1906, he failed to in- 

 clude in it the named forms speciosus, trinitatis, palmarius and fulviven- 

 ter. A consequence of the omission was a dual system of classification 

 and the multiplication of names for the eastern Venezuelan and Guianan 

 race of Oryzomys concolor. Thus, Oecomys guianae Thomas, described 

 in 1910, was compared only with marmosurus of Venezuela and tapa- 

 jinus of Brazil, while Oecomys splendens Hayman was described in 1938 

 as the first Trinidad record of arboreal rice rats. 



The two specimens from Auyan-tepui, on which the description 

 of Oecomys auyantepui Tate is based, are colored like other mainland 

 representatives of speciosus. Then- shorter hind feet and narrower 

 zygomatic plates, however, are more nearly as in 0. bicolor. A skull 

 only from Kartabo, British Guiana, also has the narrow zygomatic 

 plate. Its small molars also indicate aflanity with 0. bicolor. Osten- 

 sibly, the large and small species of arboreal rice rats have not diverged 

 as widely in the Guianan region as they have elsewhere. 



