136 Mr. 0. Thomas on 



lenjrtli, well-haired, grey, with tufts of yello wi.sli liairs at their 

 anterior bases. Upper surface of liands and feet vvhitisli. 

 Tail brown above, whitish on sides and below. 



Skull more angular than usual in this group. Interorbital 

 rei»'ion narrow, nearly square-edged. Biain-case low and 

 narrow. Palatal foramina extending nearly to the middle of 

 »/i\ Palate ending level with the back of m\ 



Dimensions of the type : — 



Head and body 105 millim. ; tail 78; hind foot (s. u.) 23; 

 ear 15. 



Skull: greatest length 26*5; basilar length 22*1 ; zygo- 

 matic breadth 14*2; nasal?, length 10; interorbital breadth 

 4"4; breadth of brain-case 11"6; palate length lO'S ; dia- 

 stema 7 ; palatal foramina 5'ii ; length of upper molar 

 series 4*2. 



Ifab. (of type). La Paz, 4000 m. 



Ti/pe. Old male. Original number 1376. Collected 28th 

 February, 1901. 



The olivaceous species of Akodon are an exceedingly 

 difficult group to make out, and I am unable at present defi- 

 nitely to determine all the large numbers of them obtained by 

 Mr. Simons during his exploration of the Andean chain. 

 From Ecuador southwards to Chili they are the commonest 

 of Muridas, and every collection contains many of them. 

 Those of Ecuador and Peru appear mo-stly to be my A.mullis^ 

 described from Tumbez, N. Peru. ^leyen's A. hoUviensis, 

 paradoxically enough, was also trom Peru, but can probably 

 never be determined with certainty, as the type is quite 

 young, and might be any one of several different forms. 



In this Bolivian collection there are three species at least, 

 and none of these can 1 identify with any described form. 

 The present one, A. pacijicus, is of much the size and general 

 appearance of the ordinary Andean A. mollis, but its inter- 

 parietal region is markedly narrower and more sharp-edged. 



1 am not quite satisfied about the determination of the 

 Cochabamba and Choro specimens, as they are not fully 

 adult. 



20. Akodon puer, sp. n. 



2 (J 1 ? • Choquecamate, 4000 m. 14th to 15th July, 



1901. ' 



A small species of the olive-coloured group. 



Size small. Fur thick and soft, hairs of back about 10 

 millim. in length. General colour above pale olive-grey, 

 lined with blackish (near " raw umber," llidgway). Jsides 

 tawny olive, gradually passing into dull soiled Isabella on the 



