ALLEN : MAMMALIA : MURID^. 75 



measured by Mr. Peterson, give the following: Total length, 125.4 (120- 

 135); tail vertebrae, 45.6 (42-51); hind foot, 20.4 (20-21). Eight speci- 

 mens from Coy Inlet, collected and measured by Mr. Peterson, all males 

 but one: Total length, 138.5 (130-144); tail vertebrae, 52 (43-60); hind 

 foot, 20 (19-20). 



The principal measurements of 4 adult skulls are : Total length, 22.9 

 (22.3-24); greatest width of brain case, 10.8 (10. 7-1 1). 



Represented by 95 specimens, collected partly in the coast region and 

 partly on the upper Rio Chico and the plains southeast of Lake Buenos 

 Aires. ' The coast specimens comprise 4 taken near Mount Observation, 

 February 21, by Mr. Colburn, and 35 from points further southward, 

 taken by Mr. Peterson, as follows : Rio Gallegos, 2 specimens, May 23 ; 

 Halliday Ranch, mouth of the Rio Gallegos, 3 specimens, June 24; Cape 

 Fairweather, 13 specimens (all males), July 5-13; Rudd Ranch, near 

 Cape Fairweather, 8 specimens, July 27 and 28 ; Coy Inlet, 9 specimens, 

 August 8 and 31, September i, and November 7-1 1. The specimens 

 from the interior include 14 specimens collected on the upper Rio Chico, 

 by Mr. Peterson, January 31 (7 specimens), February 3-6 (5 specimens), 

 and March 26 (2 specimens) ; and 34 collected by Mr. Colburn at Basalt 

 Canons, April 8-28, and 5 at Swan Lake (March 18-20 and May 4 

 and 15). 



The summer and fall specimens from the interior are darker and grayer 

 and much less fulvous than the winter specimens from the coast, but there 

 are enough specimens collected at intermediate dates to show that the 

 difference is, almost beyond question, seasonal and not geographical. 



The species thus seems to range across southern Patagonia from Cape 

 Fairweather to the Cordilleras. It was not, however, obtained by Mr. 

 Colburn at Punta Arenas, where he collected only A. xanthorliimis. 



The two specimens on which the species was originally based by 

 Waterhouse were collected by Darwin, one at Port Desire and the other 

 at Santa Cruz. Only Port Desire is mentioned in the original descrip- 

 tion, but in the Voyage of the "Beagle" (Mamm., /. c.) the "habitat" is 

 given as "Santa Cruz and Port Desire (December)." Both these specimens 

 are still preserved in the British Museum and have been compared with a 

 large number of specimens from the present series. These types are Nos. 

 " 55-12-24-157. Loc. Santa Cruz, Ex Coll. C. Darwin," and "55-12-24- 

 143. Loc. Port Desire, Ex Coll. Ch. Darwin," marked as the type of A. 



