474 Mr. 0. Thomas on new 



Skull apparently without marked characteristics. 



Dimensions of the type : — 



Head and body 139 mm. ; tail 90 ; hind foot 30-5 ; 

 ear "2'). 



Skull : greatest length 36*8 ; condylo-incisive length 33'() ; 

 zygomatic breadth 19'7 ; nasals 16' 6 ; breadth of braiii- 

 caso 1.5*6 ; palatal foramina 9"8 ; upper molar series 6'8. 



Hub. Otro Oerro, Catamaroa. Alt. 3000 m. 



Ti/pe. Adult male. 13.M. no. 20. 3. 17. 23. Ori^'iual 

 nuniber 808. Collected 13th November, 1919, by E. Biidin. 

 Prt'sented by Oldfield Tliomas. Seveii specimens. 



The species of Reitlirodon are all exceedingly clostdy 

 allied, so far as the characters of their skulls and teeth are 

 concerned, these being almost the same in all. But the 

 geographical forms may be distinguished by colour and by 

 the degree of hairiness o£ the soles, the southern cuniculoides, 

 hatcheri^ and flammarum having the plantar hairs coming 

 forward to the anterior pair of sole-pads, the intermediate 

 auritus, Desm. (with which my pamparum is probably syno- 

 nymous), having the main mass of the hairs ceasing at the 

 ])OSterior pair of pads, l)iit with a certain number of hairs 

 between tlie pads. Finally, the more northern forms from 

 Uruguay, Corrientes, and now that of Catamarcaall have the 

 pad region naked. 



In colour all l)ut caurinus have the belly mostly buffy, but 

 in aiiritus of Buenos Ayres Province the thighs are white iu 

 front. 



The type-locality of anritus was the Pampas south of 

 l^uenos Ayres, and in this region there seems to be no animal 

 but a Jieithrodon which can be fitted to Azaia's clescriptiou 

 of his " rat oreillard," the basis of Desmarest's Mus auritiis. 

 My Reithrodon cuniculoides ^^antpanus would therefore be a 

 synonym of a«ri7?<.<», unle.«s a form with less bufTy on the 

 lieliy proves to occur in the open country just south of 

 Buenos Ayres itself. 



But in the less dry south-eastern corner of Buenos Ayres 

 Province there is a duller form, due no doubt to more saturate 

 conditions, which may be distinguished as 



Ittithrodon aiirilus ntarinus, subsp. n. 



Essential characters of true aiirifus, but duller throughout, 

 less bufll'y, the ears almost unifornily (larl<, without bright 

 bulTy metentote, the under surface wholly dull greyish washed 

 with buffy, the inguinal region and front of thighs not while 

 as in aitrilics. 



