530 



PROCEEDINGS OF THE NATIONAL MUSEUM 



Table 2. — Oryzom3's (Oryzomys) alfaroi gracilis Thomas: External measurements 

 (in millimeters) of a series of adults from Valdivia, Antioquia, central Colombia. 

 Specimens were collected and measured in the flesh by the author. Note proportional 

 length of hind foot and compare with table 1. 



Members of|the^Or?/2om?/6 longicaudutus group, or subgenus Olig- 

 oryzomys, are the only other rice rats that resemble Oryzomys bicolor. 

 They are smaller, primarily terrestrial'^mice, with pelage compara- 

 tively coarse, underparts sometimes pure white, as in 0. bicolor but 

 more commonly with the color of the basal portions of the hairs dark 

 gray and usually showing through at the surface; tail more slender, 

 equal to or longer than combined head and body length, coarsely 

 scutulated, nearly naked and without a definable pencil; hind foot 

 narrow and comparatively longer, generally more than 23 percent of 

 combined head and body length; sole at heel not hidden by over- 

 lapping lateral tarsal hairs in the tropical zone forms; first hind toe 

 with claw barely extending beyond base of second toe, fifth hind toe 

 slender, its claw extending to base of middle phalanx of fourth toe, 

 sometimes slightly distad; skull (pi. 76) more elongate, braincase 

 narrower, bullae more inflated; anterior zygomatic plate forward- 

 projecting so that one-half its width is visible from above; supraorbital 

 region narrow, the sides concave, parallel or slightly divergent pos- 

 teriorward and never ridged or beaded; median longitudinal sulcus of 

 nasals continuing as a well marked depression over anteromedian 

 portion of frontals. 



Color and pelage: Geographic variation in color in Oryzomys 

 bicolor is insignificant from a taxonomic point of view. This is 

 remarkable in view of the extent and ecological diversity of the area 

 occupied by the animal. The usual correlation between coat color 

 and color of soil or ground cover apparent in most terrestrial cricetines 



