336 Mr. O. Thomas on the South- American 
white to their bases. Hands and feet grey. Tail blackish 
brown above, whitish below. 
Skull very like that of A. varius ; interorbital region not 
quite so broad, similarly square-edged, without definite ridges. 
Incisors slightly more slender. 
Dimensions of the type :— 
Head and body 98 mm.; tail 79; hind foot 24 ; ear 18. 
Skull: greatest length 28°5 ; condylo-incisive length 27 ; 
zygomatic breadth 14°7; nasals 10:2; interorbital breadth 
4°6; breadth of brain-case 12°2; palatilar length 12°6; 
palatal foramina 7; post-foraminal palate 4; upper molar 
series 4°9. 
Hab. Tucuman. Type from Villa Nouges, San Pablo. 
Alt. 1200 m. 
Type. Adult male. B.M. no. 2.1.5.8. Original num- 
ber 1365. Collected 22nd September, 1901, by L. Dinelli. 
Presented by Oldfield Thomas. Six specimens. 
While this species resembles A. varius in tne buffy or clay- 
colour of the dorsal suffusion, it differs by the contrasted grey 
of the head, shoulders, flanks, and hips, which give it a decep- 
tive resemblance to the species of Abrothriz. But there is 
no doubt that its nearest relationship is with the first-named 
animal. Its peculiar white chin is unique, but I should not 
lay very much stress on this character, which may easily 
prove variable. ; 
XL.—The Grouping of the South-Amertcan Muridse 
commonly referred to Akodon. By OupFirtp THOMAS. 
(Published by permission of the Trustees of the British Museum.) 
In his ‘Mammals of Patagonia’ Dr. J. A. Allen has drawn 
attention to the composite nature of what is usually called 
Akodon, and has indicated one or two groups which he thinks 
ought to be generically or subgenerically distinguished—for 
example, those named below Chaleomys and Chreomys. 
I have now had an opportunity to examine the whole 
group, which I find—uniform as it is in essential characters, 
and notably in the hypsodontism and general structure of the 
teeth—may be subdivided into seven genera. Of these, three 
—Akodon, Abrothrix, and Zygodontomys—were previously 
provided with names, while four need new ones. Two of 
these four are inhabitants of the Andean plateau and two 
of the lowlands of Brazil. A special subgenus is also made 
for A. wrosus, A. urichi, and their allies. 
