small Mammals from Salta and Jujuy. 191 



holes are deep narrow slits instead of being round. M 1 lias 

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

 external more cylindrical; the usual median external one 

 practically obsolete. M 2 with three roots, m* with two. 

 Pattern of unworn teeth not yet known. 

 Genotype. Hypsimys budini, sp. n. 



This genus, while closely resembling Akodon 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 hypsodont 

 Akodon, and has no near relationship to other hypsodont 

 genera, such as ChinchiUula or Andinomys, which belong to 

 different groups of the subfamily. Its discovery is a most 

 interesting addition to our knowledge of South American 

 Muridae, no very hypsodont 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 and general appearance very much as in Akodon 

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

 close that the two were supposed 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 mm. ; tail 68 ; 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 12'2; palatilar 

 length 24 ; palatal foramina 6'8 ; upper molar series 

 crowns 4'3, alveoli 4*9. 

 Hab. 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 



