184 Mr. O. Thomas on 
Size rather less than in leucodactylus, but still as in the 
larger species of the genus. Fur close and thick, hairs of 
back about 10-11 mm. in length. General colour lined 
greyish buffy brown, not so definitely buffy as in some of 
the more northern species. Under surface greyish white, the 
hairs buffy at base, white terminally in the type, slightly 
tinged with bufty in the paratype. Line of demarcation on 
sides not sharply marked. Ears large, brown, not strongly 
contrasted with the general colour. Hands and feet with 
the characteristic coloration found in R, leucodactylus, the 
metapodials mesially brown, the digits and edges white. 
Tail long, uniformly brown, not very heavily haired for this 
genus. 
Skull rather smaller than that of leucodactylus, of normal 
shape. Nasals narrow. Interorbital region not very broad. 
Palatal foramina well open, extending back past the level of 
the front edge of m!. Mesopterygoid fossa narrow, the 
palation with a well-marked median projection. 
Dimensions of the type :— 
Head and body 154 mm.; tail 180; hind foot 31:4; 
ear 24. 
Skull: greatest length 36°5 ; condylo-incisive length 34:5 ; 
zygomatic breadth 20; nasals 13; interorbital breadth 5°6; 
palatilar length 15°2 ; palatal foramina 8 x 3'2; postforaminal 
palate 5°6 ; upper molar series 6:2. 
Hab. Sierra de Santa Barbara, 8.E. Jujuy. Type from 
Sunchal, 1200 m. 
Type. Adult male. B.M. no. 21.1.1.17. Original num- 
ber 1025. Collected 6th June, 1920, by E. Budin. Pre- 
sented by Oldfield Thomas. ‘Two specimens. 
This is a considerable southern extension of the genus 
Rhipidomys, which had not previously been known to occur 
in the Argentine. The species is allied to the Peruvian 
R. leucodactylus. 
Akodon sylvanus, sp. n. 
A large species of the arenicola group. 
Size large. Colour dark finely ticked olive-brown, darker 
than in most species of the group, varying according to the 
light between “olive-brown” and “deep olive.” Under 
surface dull fuscous, the ends of the hairs dull greyish 
without marked buffy wash; chin not whitened. Ears with 
proectote black edged with buffy, metentote mixed black and 
buffy. Hands and feet dull brownish. .Tail brown above, 
whitish below. ae 
Skull large, smooth and rounded, broadevand heavier than 
