AprRIL, 1914. MAMMALS OF NORTHERN PERU — OscGoop 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 O. stolzmannt, from which its large feet and ears, 
its very long tail, and its paler under parts at once distinguish it. 
Oryzomys xanthzolus Thomas. 
Thirty-four specimens: Balsas, Marafion River (1), 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 Marafion 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. xantheolus. Oryzomys baront from Cajabamba (8,000 ft.) 
is a very closely related form, at most a highland representative of 
xantheolus. 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 O. baront may prove indis- 
tinguishable from xantheolus, in which case there would be nothing 
anomalous in its occurrence in the Marafion valley. The type of baront 
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 xanthe@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 xantheolus baront. 
