neiv Neotropical Mammals. 281 



General colour above soft favvn-giey, uniform on heal anil 

 back. Under surface greyish white, fairly well defin^Ll, the 

 basal two thirds slaty, the tips dull white. Ears short, about 

 as in ordinary Akodons, their hairs coloured like the back. 

 Upper surface of hands and feet white ; pollex with a stout 

 claw; other fingers with long powerful claws quite similar to 

 those of Akodon megalonyx and macronyx and quite unlike the 

 feeble claws of the other Reithrodons ; claws on toes large, 

 but far smaller than those on fingers ; fifth hind toe, without 

 claw, reaching to the middle of the first phalanx of the 

 fourth. Tail about half as long as the trunk, well-haired, 

 pale fawn above, white on the sides and below. 



Skull, though larger and heavier, on the whole most nearly 

 allied to that of B. chi n chill oides, the type of the '' Euneomys " 

 section of the genus. Nasals decidedly expanded anteriorly, 

 just surpassing the premaxillas posteriorly ; supraorbital edges 

 square, not ridged, their anterior end marked by a slight 

 projection, like, though too far forward to be, a rudimentary 

 postorbital process ; fronto-parietal suture evenly curved ; 

 interparietal broad, its anterior edge slightly concave forwards ; 

 anterior zygoma-root almost as in R. chinch illoides, but with 

 a sh'ght concavity on its front edge where the deep under- 

 cutting occurs in the other species ; palatal foramina widely 

 open anteriorly, reaching back to the level of the front of 

 7??.^; palate ending just behind m.^; pterygoid fossee shallow. 

 Incisors, both upper and lower, very broad, the grooves ou 

 the former well defined. Molars broad and powerful. 



Dimensions of the type (an adult specimen, measured in 

 skin) : — 



Head and body 119 millim.; tail 53; hind foot (wet) 

 s. u. 22, c. u. 25; longest fore claw (above) 6'd. 



Skull : greatest length 35 ; basilar length from hen- 

 selion29; greatest breadth 20"5; nasals 16x6; interorbital 

 breadth 4'4, interparietal 3*1 x 10'5 ; palate length from 

 henselion 17; diastema 10; anterior palatine foramina 8'5 ; 

 length of upper molar series 6'5. 



Hab. Salta Province, N. Argentina. 



Type B.M. no. 99. 2. 22. 25 *. Presented by the La Plata 

 Museum through Dr. F. P. Moreno. 



This most interesting new form bears to the other Reithro- 

 dons precisely the relation that Akodon megalonyx and 

 macrovyx do to the other Akodons, being similarly more 



* The skull should be taken as the type if it were hereafter shown not 

 to belong to the skin ; but it was extracted in the Museum on arrival, so 

 that any mistake seems quite impossible. 



