APRIL, 1914. MamMmars or NORTHERN PERU — Oscoop 163 
The white is thus strongly contrasted but only visible in a prepared 
specimen on parting the long soft hair. In the living animal it could 
scarcely be visible under any normal circumstances, and therefore its 
_ raison d’étre, if any, is probably involved in phylogeny. 
The group represented by the ndme Thomasomys stands with 
sufficient distinctness among other South American groups but this 
distinctness is perhaps less important as a biological fact than the close 
similarity which exists between this group and the North American 
generic series Peromyscus. Under the limitations of present nomen- 
clature, it is unfortunate that, while the slight distinction is recognized 
_ and emphasized, the great similarity is nomenclaturally neglected. 
Akodon mollis Thomas. 
Forty-six specimens: Menocucho (18), Pacasmayo (21), Trujillo 
(7)... 
' This is the most common rodent in the irrigated areas of the coast 
region of northern Peru. It frequents rice and cane fields and the bor- 
ders of streams and irrigating ditches, showing an obvious preference 
for moist situations. It is probably more abundant under the condi- 
tions of human occupation of the land than it would be in the absence 
of agricultural practice. 
As a species, Akodon mollis has continuous distribution from the arid 
west coast up to an altitude of at least 12,000 feet and thence across the 
mountains and down into the upper part of the eastern forest or mon- 
tagna. Speaking generally, there was no point on our route until we 
reached the Amazonian plain where we did not find some form of this 
species. Four well-marked subspecies are recognizable. Their more 
important characters may be summarized as follows: . 
Rostrum shorter and broader, zygomatic plate upright in front. 
Pelage short; color paler . A. mollis 
Pelage long; color darker A. m. altorum 
Rostrum longer and slenderer, zygomatic plate with receding front 
edge. 
Feet grayish; tail bicolor A. m. orophilus 
Feet and tail wholly blackish A. m. orientalis 
Akodon mollis altorum Thomas. 
Thirty specimens: Cajamarca (13), Hacienda Limon (4), Hacienda 
Llagueda (9), mountains near Otuzco (4). 
As in the case of typical mollis, this form was found sai aiuait about 
