164 FIELD MUSEUM or NATURAL HISTORY ZOOLOGY, VOL. 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 Maranon 

 River show slight tendency to development of the cranial characters 

 of the eastern forms orophilns and oricntalis. 



Akodon mollis orophilus Osgood. 



Fifty-one specimens: Mountains east of Balsas at 10,000 ft. altitude 

 (21), Chachapoyas (i), near Leimabamba (8), Tambo Ventija, near 

 Molinopampa (21). 



In the heavily wooded canyons, which increased in number after 

 we crossed the Maranon, 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 (i). 



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 asrosus 

 which is found slightly lower down. 



Akodon aerosus 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 1. nitidus. It was not found in 

 abundance, a line of fifty carefully placed traps seldom yielding more 

 than one specimen in a night. 



