ALLEN : MAMMALIA : MURID^. 69 



fulvous, the fulvous increasing in intensity along the lower border ; ventral 

 surface soiled white, the fur being basally very dark plumbeous and broadly 

 tipped with yellowish white ; ears dark brown on both surfaces and very 

 thinly haired, the surrounding fur concolorous with that of the anterior 

 dorsal surface ; sides of nose and lower border of cheeks whitish gray 

 with a faint tinge of yellowish ; soles naked except the posterior third, 

 dark flesh-color ; upper surface of fore and hind feet pale flesh-color, 

 nearly white ; tail one third or less than one third of the total length, 

 well clothed, dusky brown above, sides and below white. 



Mensnrements. — Total length, 175 mm.; tail vertebrae, 60; hind foot, 26. 

 Three other specimens (young adults) measure : Total length, 160 (150- 

 165) ; tail vertebrae, 57 (50-60) ; hind foot, 25 (25-25). 



Skull. — Long and narrow, the interorbital and rostral portions especi- 

 ally elongated ; postpalatal fossa narrow^ and V-shaped, but not quite so 

 narrow and pointed in front as in Reithyodo)i cunicitloides ; front border 

 of zygomatic plate as in Phyllotis, Ovyzomys, etc., lacking the pointed 

 superior process seen in Reithrodoji and Sigmodon ; bullae small and 

 pointed, as in Phyllotis ; upper incisors deeply grooved; molars brachyo- 

 dont as in Phyllotis; but very broad and heavy — not hypsodont as in 

 true ReitJirodo)i ; lower jaw short and heavy, to support the thickened 

 molars ; posterior end of lower incisors encapsuled, forming a prominent 

 process on the outer sides at the base of the condyloid process. Dimen- 

 sions (type) : Total length, 30.5 ; basal length, 26.5 ; zygomatic breadth, 

 17.5; interorbital breadth, 3.5, width of braincase, 14; length of nasals, 

 14; palatal length, 14.5; palatal foramina, 8; diastema, 8.5; upper molar 

 series, 5.2 ; width of molar', 1.8; lower jaw, length (inner base of incisors 

 to posterior bord.er of condyle), 18; height at condyle, 15; lower molar 

 series, 5.5. 



Represented by four specimens, an adult female that had suckled 

 young, and three younger specimens, nearly adult, all taken by Mr. 

 Peterson, in the Cordilleras at the head of Rio Chico de Santa Cruz, Feb. 

 8-14, 1897. These specimens are all quite similar in coloration, except 

 that the younger ones are grayer than the adults with much less fulvous 

 suftusion, and with very little fulvous on the flanks and ventral surface. 



This species finds its nearest ally in Etineomys chinchilloides (Water- 

 house), known thus far only from Tierra del Fuego, which it apparently 

 closely resembles in size and coloration. 



