Two new Rodents from Argentina. 155 



2. Akodon tartareus, sp. n. 



<?. 399. 



" Caught in a ravine on river-bank. Toes eaten by ants." — 

 E.B. 



A large vole-mouse of the varius group. 



Size very large, larger than in any of the genus except the 

 Brazilian A. arviculoides and its allies. Fur long, soft, and 

 fine, hairs of back 12-13 mm. in length. General colour 

 above greyish buffy or clay-colour becoming more intense 

 posteriorly, the rump more ochraceous tawny. Under surface 

 slaty washed with pale pinkish cinnamon, not whitish as it 

 is in varius. Chin with a white patch, as in other members 

 of this group, but it is not very conspicuous. Hands and 

 feet buffy whitish. Tail long, finely scaled, dark brown 

 above, dull buffy whitish below. 



Skull larger than in A. varius. Nasals long, much pro- 

 jected behind. Supraorbital edges sharply angular, though 

 not beaded. Interparietal rather broad antero-posteriorly, 

 short transversely. Palatal foramina reaching to the level of 

 the front of the middle lamina of m 1 . Incisive angle 73°. 



Dimensions of the type : — 



Head and body 134 mm. ; tail 94 ; hind foot 25 ; 

 ear 19. 



Skull: greatest length 31'5 mm.; condylo-incisive length 

 29*2 ; zygomatic breadth 16*6 ; nasals 12 ; interorbital 

 breadth 5*2; breadth of brain-case 13*5 ; palatilar length 

 13'5 ; palatine foramina 7*2 ; upper molar series (worn) 4 , (i. 



Hab. as above. 



Type. Adult male. B.M. no. 19. 7. 25. 2. Original 

 number 399. Collected 30th November, 1918. 



This fine Akodon may be distinguished from A. varius, its 

 nearest ally, by its larger size and by the buffy or cinnamon 

 wash on its under surface. 



3. Ctenomys sylvanus, sp. n. 



S . 395 ; ? . 396, 397, 398, 400, 402, 403. 



" In sparse colonies in the woods on vegetable soil. 5 ' — 

 E.B. 



A very dark-coloured species allied to C. budini. 



General colour above dull bistre-brown, very variable 

 according to the extent to which the slaty bases of the hairs 

 are hidden by their cinnamon-brown subterminal rings. In 

 addition, partly or wholly plumbeous specimens are in the 

 majority ; indeed, only one example, no. 397, is wholly free 

 from plumbeism, the type having a median blackish area on 

 the back. Under surface dark slaty washed with brownish 



