ALLEN : MAMMALIA : MURID^.. 79 



Adult (February). — Pelage full, soft and long. Above nearly uniform 

 hair brown with a slight yellowish suffusion ; sides of head and body and 

 under parts whitish gray, the plumbeous underfur nearly concealed by the 

 long white tips of the hairs ; ears small, thickly clothed with short hairs of 

 the color of the dorsal surface ; tail short, well clothed, bicolor, brown 

 above and whitish gray below; upper surface of fore and hind feet soiled 

 whitish with a faint tinge of flesh-color, palms and soles naked, the former 

 yellowish flesh-color, the latter similar but slightly darker. 



Measiiyeiueiits. — Four adult males measure : Total length, 174 mm.; tail 

 vertebrae, 52 ; hind foot, 25.5. Three adult females measure : Total 

 length, 174 (168-180) ; tail vertebrae, 47 (45-50) ; hind foot, 25.3 (25-26). 

 The longest fore claws have a length of 6 to 7 mm., the longest hind 

 claws measure 4 to 5 mm. 



Skull (adult female) : Total length, 30 ; basal length, 26 ; greatest 

 breadth, 14; interorbital breadth, 5; length of nasals, 12; palatal length, 

 13 ; diastema, 8 ; palatal foramina, 7 ; upper molars, 5. 



This species is represented by 9 specimens taken on the upper Rio 

 Chico, near the Cordilleras, in February, 1897, by Mr. O. A. Peterson. 

 They are all adult and very uniform in coloration, but vary a little in gen- 

 eral tone, from yellowish brown to reddish brown. 



Its nearest known relative is the A. iiiacronyx Thomas, decribed from 

 the " east side of the Andes, near Fort San Rafael. Province of Mendoza," 

 with which Mr. Thomas thus compares it: "General appearance and pro- 

 portions very much as in A. (C) niacronyx Thos., but colour darker, tail 

 more distinctly bicolor, and skull broader and flatter." He says further: 

 "This species is the southern representative of A. niacronyx Thos., to 

 which it is no doubt very nearly allied ; but the fresh series now avail- 

 able indicates that it should have a name of its own." 



Specimens from the Rio Chico, Cordilleras, Patagonia, were sent some 

 years ago by Dr. Merriam to Mr. Thomas for identification, and were 

 labelled by him as '' Akodon niacronyx, Thos." With these specimens 

 before me, I accepted this identification in preparing my account of this 

 species, written two years ago, but added: "The type locality of this 

 species \A. niacronyx] is near Mendoza, nearly a thousand miles to the 

 northward, and in all probability the southern form here described will 

 prove separable from true A. niacronyx, at least as a subspecies, on com- 

 parison with a good series of Mendoza specimens." Being without ma- 



