APRIL, 1914. MAMMALS or NORTHERN PERU OSGOOD 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'etre, if any, is probably involved in phylogeny. 



The group represented by the name 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. moll-is 



' 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 principally about 



