APRIL, 1914. MAMMALS OF NORTHERN PERU OSGOOD 157 



that the above-described species requires a name. It inhabits a wholly 

 different region on the west slope separated from the eastern montagna 

 by practically the entire Andean chain. So far as known, it needs 

 comparison only with 0. stolzmanni, from which its large feet and ears, 

 its very long tail, and its paler tinder parts at once distinguish it. 



Oryzomys xanthaeolus Thomas. 



Thirty -four specimens: Balsas, Maranon River (i), Hacienda 

 Limon, near Balsas (5), Pacasmayo (7), Menocucho (13), Trujillo (8). 



This rat was common at all localities on the coast where collecting 

 was done. It lives in thickets and weed patches along streams and 

 irrigating ditches. With the exception of Akodon, rodents were very 

 scarce in the bottom of the Maranon canyon, and the specimens of this 

 species obtained there are mostly immature and not satisfactorily dis- 

 tinguishable from the typical form of the coast region. Their under 

 parts average more nearly white, but this is a variable feature. The 

 climatic conditions at Balsas are not greatly different from those of the 

 coast, the temperature averaging high and the rainfall being slight. 

 A number of birds and plants not found in the directly intervening 

 country are common to the two regions. Possibly certain points to the 

 northward afford opportunity for the continuous distribution of these 

 and of O. xanth&olus. Oryzomys baroni from Cajabamba (8,000 ft.) 

 is a very closely related form, at most a highland representative of 

 xanihaolus . It was not taken at Cajamarca nor in the Otuzco region, 

 localities more or less flanking Cajabamba and of similar elevation, but 

 collecting conditions are such in these places that it might easily have 

 been missed. It is even possible that 0. baroni may prove indis- 

 tinguishable from xanthfBolus, in which case there would be nothing 

 anomalous in its occurrence in the Maranon valley. The type of baroni 

 and one topotype loaned by the American Museum of Natural History 

 through Mr. R. C. Andrews show no important external characters 

 when compared with series of xanth&olus from the coast. The skull of 

 the topotype, which is adult with teeth beginning to wear, can be 

 duplicated among coast specimens; but that of the type, a very old 

 female with the crowns of the teeth practically worn away, differs from 

 the coast specimens of similar age in greater size and in rostrum and 

 nasals so much heavier and wider that individual variation cannot 

 safely be taken as a sufficient explanation. Such close relationship, 

 especially in the unwieldy and slightly understood genus Oryzomys, 

 seems best indicated by the trinomial Oryzomys xanth&olus baroni. 



