164 Fretp Museum or NAtTuRAL History — Zo6.oey, Vou. X. 
cultivated fields. It differs from mollis only in slightly darker color 
and heavier pelage, characters which often appear slight on comparison 
of single examples but which are quite obvious when small series are 
considered. Specimens from Hacienda Limon just west of the Marafion | 
River show slight tendency to development of the cranial characters 
of the eastern forms orophilus and ortentalts. 
Akodon mollis orophilus Osgood. 
Fifty-one specimens: Mountains east of Balsas at 10,000 ft. altitude 
(21), Chachapoyas (1), near Leimabamba (8), Tambo Venta near 
Molinopampa (21). 
In the heavily wooded canyons, which increased in number after 
we crossed the Marafion, this mouse was found associated with Thom- 
asomys, Rhipidomys, and Oryzomys albigularis and it generally out- 
numbered any of these. It was found also in open swamps at high alti- 
tudes living in long grass or rushes quite after the manner of northern 
voles of the genus Microtus. In certain of these places, the labyrinthine 
runways, open burrows, and fresh grass cuttings so familiar to the 
northern collector were found in great numbers. In other places, as 
for example heavy woods or rocky stream beds, the Akodons seemed to 
lead wandering lives and have as retreats only natural openings in or 
near the ground. 
Akodon mollis orientalis Osgood. 
Four specimens: Poco Tambo, about 50 miles east of Chachapoyas 
(3), Tambo Almirante, near Uchco (1). 
This is the easternmost form of the mollis group. It inhabits the 
dense, humid, but relatively cool forest which forms the practically 
unbroken cover of the lower slopes of the eastern Andes. In this 
region it is possible that its range may overlap that of Akodon erosus 
which is found slightly lower down. 
Akodon wrosus Thomas. 
Ten specimens: Tambo Yaku (3), Moyobamba (7). 
This is a species of the heavy eastern forest where it lives in dense 
vegetation in company with Oryzomys Ll. nitidus. It was not found in 
abundance, a line of fifty carefully placed traps seldom yielding more 
than one specimen in a night. 
