Rodents from Western South America. 301 



different P. brevicauda, Giinth. Its most obvious diagnostic 

 characters are its thinly haired, large-scaled tail, its sharply 

 defined white belly, its small skull, suppressed parietal ridges, 

 and short open palatal foramina. 



In his description of P. brevicauda * Dr. Giinther speaks 

 of " an adult male in spirit and the skin of an adult female 

 brought by Mr. E. Bartlett from Chamicuros, Huallaga 

 River"; but, as a matter of fact, it is only the skin 

 (received in 1869) that is labelled as from Chamicuros, and 

 the spirit-specimen is merely recorded from the Upper 

 Amazon, and was received by the Museum three years 

 before, in 1866. It is therefore probable that they are from 

 different localities, and there is unquestionably great doubt as 

 to their specific agreement. Under these circumstances it 

 would be advisable to treat the skin by itself, accurately 

 labelled and with good skull, as the type, and to ignore the 

 second specimen, which has no exact locality and whose skull 

 is broken to pieces. 



Ctenomys tucumanus, sp. n. 



Size small, about as in C. talarum. General colour above 

 brownish fawn, with a faint reddish suffusion ; middle line of 

 face blackish. Cheeks like back, a faint lighter patch below 

 ear. Under surface pale buffy, the hairs plumbeous basally ; 

 large white axillary and inguinal patches present, the former 

 almost extending across the chest (but this may be due to the 

 great age of the specimen, which is also becoming hoary on the 

 back). Upper surface of hands well haired, whitish, of feet 

 nearly naked, the few hairs also white. Tail practically 

 naked, a few whitish hairs forming a slight terminal crest. 

 This nakedness of hind feet and tail is possibly due to age 

 and wear. 



Skull broad and flattened, much more so than in C. mendo- 

 cinus } and still more different to the lumpy rounded skull 

 of G. Perrensi. Nasals evenly tapering backwards, their 

 posterior end behind the level of the anteorbital bridge. 

 Interorbital region flat, shorter and broader than in G. talarum, 

 as also is the brain-case. No interparietal discernible. Malar 

 less heavily ridged than in C. talarum. Posterior nares 

 broad and open, the pterygoid ridges much further apart than 

 in the allied species. 



Dimensions of the type (measured in the flesh) : — 



Head and body 172 millim. ; tail 71 ; hind foot, s. u. 27, 

 c. u. 30*5 ; ear 6. 



* P. Z. S. 1876, p. 749. 



