204 Mr. O. Thomas on synaU Mammals 



as to whether it ought not to be distineuished 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 stifusus and modesfior 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 ti>e 

 A. hirtus of San Rafael, Mendoza, still further to the 

 northward. 



To the list of tlie species belonginj^ to Ahrotlirix, besides 

 those mentioned in my paper on the grouping of the Akodont 

 Muridffi*, there should be added Mus brachyotis, Waterb., 

 from the Chonos Archipelago. 



All these forms of Abrothri.v 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." — E. B. 



10. Ahoclon heatus, sp. n. 



c?. 61, 8.5, 87, 91, 100, 103, 108, 109; ?. 59, 63. 

 Beatriz, Nahuel Huapi. 800 m. 



A rather large species of the arenicola group. 



Size decidedly greater than in arenicola of Uruguay and 

 Buenos Ayre-*, the hind foot averaging 1^ 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 areni- 

 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 xanthorhinus- 

 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 

 lamina of »t\ 



Incisois of about normal set, the angle 69° in the type. 

 Notch at front end of m' not perceptible in any specimen, 

 the youngest being, perhaps, three-fourths grown. 



• Ann. & Mag. Nat. Hist. (8) xviii. p. 340 (191G). 



