On Two new Argentine Rodents. 283 



broad, evenly broadening backwards, and then abruptly 

 truncated, not narrowing to a median point posteriorly, their 

 hinder margin convex backwards ; premaxillary processes 

 very narrow and slender. Zygomata strongly and evenly 

 bowed outwards, the outlines of the two, continued across the 

 muzzle, forming together three-fourths of a circle. Palatine 

 foramina long, as in G. australis, but markedly narrower. 

 Posterior palatal margin rounded, not angular, level with the 

 hinder lamina of m.^. 



Incisors slender, narrow, the upper ones more thrown 

 forwards than in other species, their front surface white. 

 Posterior talon of m.^ much less developed than in G. aus- 

 trails. 



Dimensions of the type (an adult female) : — 



Head and body (Jide Garlepp) 190 millim. ; hind foot 

 (wet) 34 ; ear (wet) 13. 



Skull : basal length 36'6 ; basilar length from henselion 

 33"5 ; greatest breadth 29*5; nasals 15x9*1; interorbital 

 breadth 11 ; palate length from henselion 18'5 ; diastema 9*3 ; 

 palatal foramina 5*5 X 2*1; length of upper molar series 

 (crowns) 10"2. 



T(/pe B.M. no. 98. 3. 16. 20; original number 1716. 

 Killed May 8, 1897. 



The only known species to which this curious little Cavy 

 is even distantly allied is G. austrah's, but that differs markedly 

 from it both in cranial and external characters. G. nicenas, 

 described in the following paper, is, on the other hand, 

 closely allied to G. australis and equally distant from 

 G. nt'ata. 



XLVI. — Descriptions of Two new Argentine Rodents. 

 By Oldfield Thomas. 



(t.) 



The British Museum owes to the kindness of Dr. F. P. 

 Moreno, of the La Plata Museum, the skin of a Cavy from 

 Kioja, obtained by him during the same expedition on which 

 he discovered the Eligmodontia Moreni described by me in 

 1896 *. In working out the Cavies collected by Mr. Garlepp 

 and referred to in the preceding paper the Rioja one also 

 proves to be new, and may be described as follows : — 



* Ann. & Mag. Nat. Hist. (6) xviii. p. 307 (1896). 



