ARBOREAL RICE RATS — HERSHKOVITZ 



531 



Table 3. — Oryzomys (Oecomys) concolor superans Thomas: External measure- 

 ments (in millimeters) of a series of adults from the Rio Caquetd region, eastern 

 Colombia. Specimens were collected and measured in the flesh by the author. 

 Note tail length and proportional length of hind foot and compare with table 4- 



is not evident in arboreal Oryzomys hicolor. The direct relationship 

 between amount of rainfall and intensity of coat color, clearly ex- 

 pressed in many species of terrestrial and arboreal mammals, is but 

 slightly indicated on the underparts of some individuals of 0. hicolor. 

 Temperature throughout the area occupied by 0. hicolor is fairly 

 uniform and has little or no effect on the length, thickness, texture and, 

 indirectly, the color of the pelage. 



The underparts vary from pure white to uniformly ochraceous. 

 White underparts may be marked by buff or ochraceous spots, patches 

 and streaks. In underparts that appear wholly white at the surface, 

 the basal portions of the hairs are generally white except, sometimes, 

 along the sides where they may be gray. Where the underparts are 

 tinged, the basal portions of the hairs are, as a rule, dark gray. 



In any one population, each adult may be classified as either bright 

 or dark according to the color of its upperparts and sides. In the 

 bright color group, the terminal portions of the cover hairs are ochra- 

 ceous orange with or without a fine dark brown tipping. The 

 terminal portions of the guard hairs are dark brown. The colors in 

 the dark group are similar but the cover hairs are more uniformly 

 tipped with dark brown and there is a greater concentration of 

 guard hairs. 



