from ''Otro Ctrro^" North-eastern Rioja. 497 



liave l)Pen tiuated for purposes of distinction. But fortunately 

 a topotype !<kin has since been received, and tliis is of tbo 

 same butty olive colour as the spociinens from Potosi referr«;d 

 to that specioH in 11U)2 *. 



^1. alteiHs is readily ilistin;^ui.sliable from the older-known 

 specii's by the absence of tlie strong yellowish or buiTy sufl'u- 

 sion in the t'ur. 



No. 228, from Ciiumbicha, erroneously referred to A.areni- 

 cola in my previous paper, also proves to belong to this 

 species, while an additional specimen, no. 317, has also come 

 Irum that locality. 



11. Akodon orbits, sp. ii. 



?. 324. 

 A proodont Akodon allied to A. lactens. 



General ciiaracters very much as in A. lactens^ the colour 

 practically the same except that there is no white patch on 

 the chin. The tone is slightly duller and more drabby, but 

 the differejice amounts to little. Ears slightly shorter, 

 coloured like the head. Fore-claws similarlv elongated, as 

 long as those of the hind leet. Tail blacdcish above, dull 

 drabby on sides and below, the ditference but little marked. 



Skull of lighter build, with markedly narrower muzzle 

 than in lactens. Upper outline more bowed. Brain-case 

 smooth, unridged. 



Incisors similarly thrown forward (proodont), the incisive 

 angle of the type 8G° ; they are light-coloured, as in ^4. 

 hictenSf but are distinctly more slender in a specimen as old 

 as or older than the type ot that animal. Molars rather 

 narrower, of similarly high solid structure. 



Dimensions of the type: — 



Head and body 1)7 mm. ; tail 50; hind foot 21 ; ear 14. 



Skull: greatest length (bone only) 26'4 ; contlylo-incisive 

 length 2.'>*2; zygomatic breadth 14'0 ; breatlth of muzzle 4*2 ; 

 nasals 9*1 ; interorbital breadth 5 ; breadth of brain-case 12 ; 

 palatine foramina 6'4; postforaminal palate 4; upper molar 

 seiies 4*8. 



Tijpe. Old female. B.M. no. 19. 2. 7. 45. Original 

 number 324. Collected 21.st August, 1918. 



This 8j)ecies is evidently closely related to A. lactens^ 

 discovered by Sr. Budin at Leon, Jujuy, but ditVers by its 

 markedly more slenderly built muzzle, thinner incisors, and 



• Ann. & Mag. Xat. Hist. (7) ix. p. 226 (lt)02). 



