ALLEN : mammalia: octodontid/E. 41 



stripe varies in distinctness from nearly obsolete to a broad, well-defined 

 black band running the whole length of the tail. 



Young in first pelage are grayer with less fulvous, and the pelage is 

 longer, softer, and less firm. 



Measurements. — Type: Total length, 208 mm.; tail vertebrae, 62; hind 

 foot, 28. Five adult males: Total length, 200 (195-208); tail vertebrae, 

 56.6 (51-62) ; hind foot, 26.2 (25-28). A single adult female measures : 

 Total length, 210; tail vertebrae, 60; hind foot, 27. 



Skull, type: Total length, 39; basal length, 35.2; zygomatic breadth, 

 24; mastoid breadth, 23.5; interorbital breadth, 7; length of nasals, 13; 

 palatal length, 17; diastema, 10; upper molar series, 7.5; lower jaw, inner 

 base of incisors to posterior border of condyle, 26 ; inner base of incisors 

 to end of angular process, 29.5 ; height at condyle, 7 ; width between 

 condyles, 15.3; width between tips of angular processes 25.6; lower 

 molar series, 8. Four adult male skulls: Total length, 36.4 (34.3-39); 

 zygomatic breadth, 21.5 (20-23.6). An old female skull measures, total 

 length, 36 ; zygomatic breadth, 20. 



In several of the skulls the interparietal is entirely absent, and when 

 present is very small. The lateral intercalated bones are present, and are 

 as variable in form as already described in Ctenomys robustits. 



Represented by 1 1 specimens, collected by Mr. Peterson in the Cordil- 

 leras of the upper Rio Chico de Santa Cruz, in the valley close to the 

 river, Jan. 31 to Feb. 7, 1897. Six are adults and five are young, partly 

 in the juvenile pelage. 



This species considerably exceeds in s\zt Ctenomys pinidti Nehring, and 

 differs from it very markedly in coloration. The total length of the skull 

 of C. piindti xs given as 31.3 mm., and the zygomatic breadth as 19.5; 

 the same for C. sericeus (average specimens) being, respectively, 39 and 

 21.5 mm. While it agrees practically in size with C. bergi Thomas, from 

 the central part of the Province of Cordova, it differs from it in color, 

 being very much darker throughout. 



Ctenomys sericeus occurs with the very much larger and very differently 

 colored C robustus, as both were collected on the same days and at the 

 same localities by Mr. Peterson. 



He says of this species: "Burrows extensively in the ground, leaving 

 piles of dirt at the surface like pocket gophers (Geomyidae). They make a 

 drumming noise while sitting in the mouth of the burrows." (MSS. notes.) 



