204 Mr. O. Thomas on small ‘Mammals 
as to whether it onglt not to be distinguished specifically. 
Besides its generally dark colour, its greyish belly, grey feet, 
and scarcely bicolor tail all help to distinguish it. But its 
skull is so precisely like that of suffusus and modestior that it 
evidently represents them in a more saturate area, and for 
the present, therefore, I retain it in connection with them. 
Perhaps, also, hereafter these forms will link up with the 
A. hirtus of San Rafael, Mendoza, still further to the 
northward. 
To the list of the species belonging to Abrothria, besides 
those mentioned in my paper on the grouping of the Akodont 
Muride *, there should be added Mus brachyotis, Waterh., 
from the Chonos Archipelago. 
All these forms of Abrothriz from the eastern slope of the 
Andes are readily distinguishable from A. longipilis of Chili 
by their far smaller skull. 
“Trapped among the roots of fallen trees.” —Z. B. 
10. Akodon beatus, sp. n. 
b2 GY, 855"87; 91, 10059105, 108) Ode eo oi game: 
Beatriz, Nahuel Huapi. 800 m. 
A rather large species of the arxenicola group. 
Size decidedly greater than in arenicola of Uruguay and 
Buenos Ayres, the hind foot averaging 13 or 2 mm. longer. 
Fur close and woolly. General colour above dark olivaceous, 
under surface greyish white (near “ light neutral grey’), the 
hairs slaty at base, white or whitish terminally, practically 
without the drabby or buffy wash generally found in arent- 
cola; as a consequence, the upper and under surfaces are 
more contrasted with each other than in the common species. 
Ears coloured like head. Hands silvery white, a little 
darkening on the metacarpus. Feet brownish, the digits 
lighter. Tail as usual longer than in the wanthorhinus- 
canescens group, rather prominently bicolor, blackish above, 
darkening terminally, whitish below. 
Skull larger than that of arenicola, with large rounded 
brain-case and proportionally narrow interorbital region. 
Palatal foramina not extending so far back, their hinder 
edge hardly reaching the level of the middle of the second 
Jamina of m’. 
Incisois of about normal set, the angle 69° in the type. 
Notch at front end of m* not perceptib'e in any specimen, 
the youngest being, perhaps, three-fourths grown. 
* Ann. & Mag. Nat. Hist. (8) xvili. p. 840 (1916). 
