304 Mr. O. Thomas on 
XXXV.—Two new Argentine Rodents, with a new Subgenus 
of Ctenomys. By OLpDFIELD THOMAS. 
(Published by permission of the Trustees of the British Museum.) 
THANKS to the hospitality of the owners of the ranche, and 
especially to the kind assistance of Don Cecil Porteous, 
Mr. Robin Kemp has been enabled to make a collection of 
small mammals at La Maria Luisa Ranche, on the Pampas 
of Buenos Ayres Province. Among the specimens so obtained 
are a series of a Tuco-tuco, which appears to be distinct from 
any described. 
It may be called 
Ctenomys porteousi, sp. 0. 
Allied to Ct. azare, but larger, with much larger bullee and 
less developed parietal ridges. 
General colour above approximately “ cinnamon-brown,” 
lined with blackish, the median area of the back darkened, 
sometimes quite to black, but the dark area not sharply 
defined. Top of muzzle and crown also blackish. Under 
surface near ‘ vinaceous buff” or rather more drabby, the 
bases of the hairs, as usual, dark slaty. Hands and feet 
buffy whitish. Tail dull whitish, drabby, or pale brown, the 
terminal crest darker, often blackish. 
Skull, as compared with that of Ct. azarae, decidedly larger 
(like sexes being compared), but of the same general shape. 
Crown smooth, the parietal ridges, which are particularly 
well marked in azar@, almost imperceptible in the oldest 
specimens. Incisive fissure of medium size, close in front of 
the palatal foramina, and in the same general hollow with 
them. Foramen magnum unusually high, with either one or 
two projections downwards on its upper edge. Bullee much 
larger than in azare, which, in turn, has them larger than in 
talarum. Incisors slightly less thrown forward than in azare 
(angle with tooth-row about 97°-100°, as compared with 
105°-108°), their front surface rather darker in colour, 
approximately “ xanthine orange.”’ 
Dimensions of adult male and female (the first the 
type) :— 
Head and body 185, 150 mm.; tail 86, 79; hind foot 
35, 32. 
Skull: length in middle line 46°5, 42 ; condylo-incisive 
length 46°5, 41°5 ; diagonal length from gnathion to back of 
bulla 48°8, 44; zygomatic breadth 27°8, 25 ; nasals 16°5, 15; 
