1 88 Bulletin American Mtiseum of Natural History. [Vol. XIX, 



In some specimens there is a tendency to a well-marked darker 

 median dorsal band, extending from the nose to the base of the tail. 

 Several of the specimens are a little darker than the type above 

 described. The tail 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 and with less fulvous, and the 

 pelage is longer, softer, and less firm. 



Measurements. Type: Total length, 208; tail vertebras, 62; hind 

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

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

 measures: Total length, 210; tail vertebras, 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 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, 2.1.5 

 (20-23.6). An old female skull measures, total length, 36; zygo- 

 matic 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 robustus. 



Represented by n specimens, collected by Mr. Peterson at 

 the eastern edge of the Cordilleras of the upper Rio Chico 

 de Santa Cruz, Jan. 3i-Feb. 7, 1897. Six are adults and 

 five are young, partly in juvenile pelage. 



This species exceeds only a little in size Ctenomys pundti 

 Nehring, but differs from it very markedly in coloration. The 

 total length of the skull of C. pundti is given as 31.3, and the 

 zygomatic breadth as 19.5; the same for sericeus (average 

 specimens) being, respectively, 36 and 21.5. While it agrees 

 practically in size with Ctenomys bergi Thomas, from the cen- 

 tral part of the Province of Cordova, it differs greatly from 

 it in color, being much darker throughout. 



Ctenomys colburni, sp. nov. 



Type, No. 147, Colburn Coll., $ ad., Arroyo Aike, in the basalt 

 canons, 50 miles southeast of Lake Buenos Ayres, Patagonia, April 19, 

 1898; A. E. Colburn, after whom the form is named. 



