small Mammals from Salt a and Jujuy, 191 



holes are deep narrow slits instead of being round. M ] has 

 one Long anterior root, one long internal one, and a postero- 

 external more cylindrical ; the nsuaJ median external one 

 practically obsolete. M- with three roots, vr with two. 



Pattern of unworn teeth not yet known. 



Genotype. Hypsimys budini, Bp. n. 



This genus, while closely resembling Akodun in external 

 characters, is readily distinguishable by its strongly deve- 

 loped hypsodontism, both roots and crowns of the teeth 

 being highly modified. It is clearly a specially liypsodont 

 Akodon, and has no near relationship to other liypsodont 

 genera, such as Chinchillula or Andinomys, which belong to 

 d liferent groups of the subfamily. Its discovery is a most 

 interesting addition to our knowledge of South American 

 Muridae, no very liypsodont member of this group having 

 been hitherto known, although a slight hypsodontism is 

 present in many of them. 



The following is a description of the type-species : — 



Size aud general appearance very much as in Akodon 

 fumeus, Thos., of Bolivia, to which the resemblance is so 

 close that the two were snpposed to be the same until the 

 skull was examined. General colour above dark olivaceous, 

 becoming warmer and browner on the rump. Under surface 

 dark greyish, washed with whitish or buffy. A distinct 

 white spot on the chin. Ears rather darker than head. 

 Hands and feet greyish, the hairs at. bases of claws white ; 

 claws comparatively long, the fourth anterior about 3 mm. 

 in length, the posterior 2"8. Tail about as long as the 

 body without the head, well-haired, distinctly bicolor, 

 blackish above, whitish below. 



Dimensions of the type (measured in the flesh) : — 



Head and body 89 nun. ; tail G8 ; hind foot 21 ; ear 17. 

 (An older specimen measures: head and body 115 mm.; 

 tail 76 ; hind foot 23.) 



Skull (of type) : greatest length 27*5 ; condylo-incisive 

 length 25' 4 ; zygomatic breadth 14; nasals 10; inter- 

 orbital breadth 4*2; breadth of brain-case 122; palatilar 

 length 24 ; palatal foramina 68 ; upper molar series, 

 crowns 4*3, alveoli 4^9. 



Hub. as above. 



Type. Young adult male. B.M. no. 18. 1. 1.44. Original 

 number 47. Collected 29th August, 1917. 



This interesting mouse is so exactly like one of the 

 ordinary Akodons that no one would suspect its real 

 peculiarities until the skull was examined. Indeed, it is so 



