On new Rodents from Western South America. 383 



XLVII. — Descriptions of new Rodents from Western South 

 America. By Oldfield Thomas. 



Ctenomys opimus, Wagn. 

 Ctenomys opimus, Wagn. Arch. f. Nat. 1848, p. 75. 



There can be little doubt that the specimen on which this 

 species was founded was one of the " large number " obtained 

 by Mr. Bridges in Potosi and other parts of Bolivia, and 

 referred by Waterhouse to C. braziliensis *. 



The Museum contains several specimens from the same 

 collector, and in addition a series of four from Tetiri, S. Peru, 

 others from Sahama, N.W. Bolivia, and an isolated example 

 from Jujuy; and these seem to represent three subspecies, of 

 which the Sahama one, as being like some of Bridges's 

 specimens, and the most like Wagner's description, may be 

 taken as the typical subspecies. The other two are as 

 follows : — 



Ctenomys opimus nigriceps, subsp. n. 



Similar in size to the typical form, or perhaps rather larger, 

 and the tail rather longer. 



Fur similarly soft and fine. General colour greyish fawn, 

 more greyish and less sandy than in true C. opimus. Whole 

 centre of face as far back as the nape prominently deep black ; 

 on the neck the black becomes much more grizzled with 

 fawn, but is traceable as an ill-defined line down the back to 

 the loins. On each side there is also a black band passing 

 through the eye and across the ear, behind which it forms a 

 distinct patch, separated from the central black of the crown 

 by a projection forward of the body-colour. The sides of 

 the muzzle and the chin are also black, behind which latter 

 there is a contrasted transverse light mark corresponding in 

 position with the rami of the mandible. Behind this again 

 the centre of throat is prominently blackish. Upper surface 

 of hands, feet, and whole of tail dark chocolate-brown ; the 

 comb-like fingers of the feet and the longer hairs at the end 

 of the tail are, however, yellowish. 



Skull as in the typical form. 



Dimensions of the type (measured in the flesh by col- 

 lector) : — 



Head and body 230 millim.; tail 100 ; hind foot (s. u.) 38, 

 (c. u.) 43. 



* X. H. Mamm. ii. p. 273. 



