550 PROCEEDINGS OF THE NATIONAL MUSEUM voL.no 



the subspecies concolor. Its belly is tinged with buffy, the hairs of the 

 throat, chest, and groins white. Oryzomys klagesi J. A. Allen, from 

 El Uagual (or Yagual), Kio Caura, farther down the Rio Orinoco, is 

 nearer true concolor than speciosus, with which it was originally com- 

 pared. Oecomys caicarae J. A. Allen is the third name given to the 

 middle Rio Orinoco population of concolor. The duskier coloration 

 of the upperparts in the type series indicates a cline leading to the 

 darker speciosus in northeastern Venezuela and Trinidad. 



Twelve specimens from the upper Rio Meta region, Colombia 

 (Villavicencio, Buena Vista, Mambita, Guaicaramo, Medina), repre- 

 senting Oryzomys helvolus J. A. Allen and vicencianus J. A. Allen agree 

 with concolor of the upper Rio Negro-Rio Orinoco region in size, but 

 are more saturate on underparts and as dark on upperparts and sides 

 as 0. concolor superans. An extremely large female from Guaicaramo, 

 like the type oi frontalis, is equal in size to average adult superans. 

 Morphologically and geographically, however, the mice of the Colom- 

 bian base of the Andes in Orinoco drainage are nearest true concolor. 



Thirty-six topotypes oiflavicans Thomas from Merida, Venezuela, 

 vary remarkably little inter se. Their upperparts are uniformly pale, 

 their bellies whitish with a light to moderate, never a heavy, bufTy 

 wash. 



Thi'ee mice from La Azulita in the Maracaibo basin at the foot of the 

 Sierra de Merida are indistinguishable from the Merida series. A 

 specimen from Rio Cogollo on the Sierra de Perija side of Lake 

 Maracaibo is brighter above, more buffy beneath, and quite like 

 individuals from the Colombian side of the same mountain range. 



The relationship of the intensity of body color to rainfall is shown 

 by specimens from diverse localities in the Sierra Nevada de Santa 

 Marta. The darkest specimens are from the humid Don Diego region 

 at the base of the mountains. Topotypes of illectus Bangs from the 

 equally humid but cooler northern slope of the Sierra average paler. 

 A series from the humid locality of Pueblo Bello on the southern side 

 of the range is colored like topotypes of illectus. In the warmer, less 

 humid El Salado, farther down the eastern slope, the mice average 

 paler. Thirteen specimens from the comparatively dry Rio Cesar 

 valley (VUlanueva; El Orinoco) between the Sierra Nevada and 

 Sierra de Perija are smaller and extremely pale, their underparts more 

 nearly pure white. They were taken from the early part of the dry 

 season in January to the beginning of the rainy season in April. The 

 January specimens are darkest, their pelage in good condition. In 

 the March specimens, the pelage is faded and molting. April speci- 

 mens show the darker new pelage on the middorsal region. The 

 contrast is quite marked between the pale, comparatively short-haired 

 valley mice of the dry season and the saturate prime pelage of speci- 



