240 PROCEEDINGS OF THE NATIONAL MUSEUM. 



M. mimMs) ; palatilar length, 11.8; palatal foramina, 6.5; upper mo- 

 lar series, 4.5. 



Ty2}e.—0\di male from Maclm Picchu, U.S.N.M. No. 194607. 

 Original No. 276. Collected May 28, 1915. 



Fifty-eight specimens, as follows : 



Torontoy, 9,500-14,000 feet, 39 (Nos. 194581-2, 191595, 194602^, 

 195025-57). 



Machu Picchu, 8,000-13,000 feet, 11 (Nos. 194605-8, 194610-11, 

 194619, 194676-7, 194693, 194745). 



Ocobamba Valley, 9,100 feet, 3 (Nos. 194632-3, 194635). 



Quirapata, 11,400 feet, 5 (Nos. 194647-9, 194680-1). 



This species is distinguishable from M. mimns by its broader and 

 less characteristically Microxine zygomatic plate, but is otherwise 

 very similar to that animal. Osgood's Akodon mollis orophilus is 

 said to be " more fulvous than A. m. altorumy which is anything but 

 the case with the present animal; and his A. m. orientalis is a low- 

 land form and much darker in color. 



The proper treatment of this animal is a most difficult j)roblem 

 on account of its annectant characters. Originally two groups were 

 known, Akodon with normal claws and vertical zygomatic plate, and 

 Oxyrriycterus with elongated claws and slanting plate. Then cer- 

 tain species were discovered which had normal claws and slanting 

 plate, and for these, after they had been referred either to Akodon 

 or Oxymyctenis^ I formed the genus Microxus^ with M. mimus as 

 genotype. Next Mr. Osgood, getting a pair of forms, respectively 

 lowland and highland, corresponding to the Akodon surdus and Mi- 

 croxus torq^ues of the present paper, treated them merely as sub- 

 species of a common form, Akodon mollis, a treatment which appears 

 to me to give far too little value to the characters of the zygomatic 

 plate. 



But, on the other hand, I quite admit that while the zygomatic 

 plate of the earlier described species was strongly and characteristi- 

 cally different from that of Akodon, that of M. torques (and I pre- 

 sume of Akodon m,oUis orofhllus and orientalis) is more or less inter- 

 mediate between the two. We. have therefore to decide whether 

 Microxus shall be amalgamated with Akodon, ignoring its peculiar 

 zygomatic plate, or whether we shall recognize Microxus and put 

 torques, orophilus, and orientalis into it, where they would form a 

 group of species annectant with Akodon. Although I am by no 

 means completely satisfied this latter course seems on the whole the 

 most advisable for the present, and I have therefore treated Mr. 

 Heller's animal as a member of the genus Microxus. 



The above was written before the spirit specimens came into my 

 liands. A study of these shows very strongly the essential difference 



