ARBOREAL RICE RATS — HERSHKOVITZ 551 



mens taken during the rainy season on the comparatively cool slopes 

 of the Sierra Nevada and the Sierra de Perija. 



Oryzomys trichurus J. A. Allen is founded on a juvenal and Oecomys 

 mincae J. A. Allen on an adult, both from localities near Bonda in 

 the semiarid northwestern corner of the Sierra Nevada de Santa 

 Marta. They are like the small pale mice of the ecologically similar 

 valley at the western base of the Sierra. One specimen at hand from 

 Bonda is virtually a dwarf. 



The range of variation in color, size, and degree of development of 

 the supraorbital ridges shown by the mice of the Sierra Nevada de 

 Santa Marta region is greater than in those of any other single region. 

 The tendency for each stream valley branch in each altitudinal zone 

 to produce a distinctive population is one of the most striking bio- 

 logical phenomena of the Sierra. 



Oryzomys flavicans subluteus Thomas from "W. Cundinamarca," 

 Colombia, was described as similar to Y enezuelan flavicans "but dis- 

 tinguished by its darker belly." Three specimens at hand from 

 Paime, Rio Minero, western Cundinamarca, with underparts lightly 

 washed buffy are absolutely indistinguishable from topotypes of 

 flavicans. Two specimens from Muzo, western Boyacd, and but a 

 few miles downstream (north) from Paime, with underparts entirely 

 buff except for the white throat and chin are exactly like the type of 

 subluteus. 



Oryzomys tectus Thomas was described as more brightly colored 

 ih^SLTi. flavicans and with "remarkably expanded supraorbital ridges." 

 The difference in color between western Panamanian tectus and Vene- 

 zuelan flavicans lies well within the limits of variations common to 

 any large population from either region. Supraorbital ridges are 

 present in all members of the species and are more prominent in older 

 than in younger individuals. It is true, nevertheless, that the ridges 

 are more uniformly developed and ledgelike in most Central Ameri- 

 can and western Colombian mice than in many other series of the 

 subspecies. 



Western Colombian (Socorre, Puri, Catival) mice are indistinguish- 

 able from their Panamanian relatives. In one specimen from Pun, 

 Antioquia, the upperparts and sides are grizzled with an interspersion 

 of wholly white cover hairs. A female from Socorre, upper Rio Sinii, 

 Cordoba, shows the molt from dark to bright pelage. 



The nsLine frontalis Goldman is based on eastern Panamanian mice 

 that are less tawny above and less buflpy beneath than the average of 

 western Panamanian tectum. The difference, although locally con- 

 stant, is slight. 



Remarks : The original description of Hesperomys concolor includes 

 the following Latin diagnosis: "H[esperomys] fulvus, subtus abrupte 



