ALLEN: mammalia: murid^. 6i 



gray below thinly clothed with short hairs in young specimens, nearly 

 naked in adults ; upper surface of the feet yellowish white or nearly flesh- 

 color ; palms and soles naked, the former yellowish flesh-color, the latter 

 darker, more brownish. 



Voiuig specimens differ little in color from the adults, but the pelage is 

 of a softer, more woolly texture. 



Measiireuients. — Eight adult males measure: Total length, 221 mm. 

 (212-237) ; tail vertebrae, 92 (85-100) ; hind foot, 29 (27-30). Ten adult 

 females measure: Total length, 221 (215-235); tail vertebrae, 93 (85- 

 100) ; hind foot, 29 (28-30). A young adult and an adult skull measure 

 respectively : Total length, 29.5, 32 ; basal length, 25, 28 ; zygomatic 

 breadth, 17, 19 ; mastoid breadth, 8, 9.5 ; interorbital breadth, 3.8 ; length 

 of nasals, 7.3, 8 ; palatal length, 13, 15 ; palatal foramina, 7, 7.4 ; diastema, 

 7, 8 ; upper molar series, 5.2, 5.3. 



Of the fifty specimens of this species about one half are fully adult, the 

 rest being more or less immature, but mainly "young adults." Four were 

 collected by Mr. Colburn — two at Swan Lake in March, and two at Basaltic 

 Canons in April — and the rest by Mr. Peterson, nearly all during the 

 first half of February (January 31 -February 17), and mostly in the Rio 

 Chico valley, close to the river. Two others were taken on the Pacific 

 slope in March. 



The coloration of the upper parts is very uniform throughout the series, 

 varying slightly in general tone on the back from yellowish brown to a 

 slight rufescent tinge, the latter seeming to characterize very old specimens. 

 The whitish gray ventral surface varies from a slight tinge of deep buff 

 over a limited portion of the middle region to a much deeper rusty buff, 

 covering a much larger area. Some specimens quite lack the buffy 

 wash. 



A portion of the specimens forming the present series was identified by 

 comparison with Waterhouse's type, still extant in the British Museum 

 — a fairly well preserved skin with an imperfect skull. This specimen, 

 according to Darwin's note, was " caught in the interior plains of Pata- 

 gonia, in latitude 50°, near the banks of the Santa Cruz." 



Mr. Peterson states (MSS. notes) that this is the most common species 

 met with on the " Rio Chico Cordillero, especially in the heavy grass 

 near water ; but was also caught in timber at some distance from water." 

 It appears to have been rare further north in the more open country where 



