On a new Tuco-tuco from Tucuman. 243 



XXX. — 'A new Tuco-tuco from Tucuman. 

 By Oldfield Thomas. 



(Published by permission of the Trustees of the British Museum.) 



Ctenomys occultus, sp. n. 



A small species nearly allied to 0. juris. 



Size rather less than in juris. Colour rather a warmer 

 tinge of brown, more as in C. bergi and Jatro; upper surface 

 glossy cinnamon-brown with some vague darkening on the 

 crown, but without a definite blackish forehead. Under 

 surface broadly washed with pale drabby, the chin and throat 

 stronger drabby ; some specimens are more whitish below, 

 while among the examples of juris some are inclined to be 

 drabby ; but on the average occultus is decidedly more 

 drabby, especially anteriorly, than juris. 



Skull agreeing with that of juris in its small bulla?, proodont 

 incisors, and the presence of a small sharp-edged ledge pro- 

 jecting over the orbital fossa?, the notch in front of these 

 ledges shorter, sharper, and more abruptly cut out than in 

 other species. Bullae slightly larger than those of juris, 

 though agreeing essentially with them ; in bergi and fochi 

 they are decidedly larger than in either. Zygomata widely 

 spaced, their middle region markedly more convex" outwards 

 than in juris. Palatal foramina with the small median ad- 

 ditional foramen just in front of them much smaller and 

 less conspicuous — indeed, hardly perceptible in some speci- 

 mens. Palation level with the middle of m 2 . Bulla? averaging 

 slightly larger than in juris, though agreeing essentially with 

 them. 



Incisors rather proodont, index about 102°-104°. Molars 

 smaller than those of C. juris. 



Dimensions of the type : — 



Head and body 138 mm. ; tail 55 ; hind foot 26'5. 



Skull : median length 38*7 ; condylo-incisive length 37'8; 

 zygomatic breadth 25'2 ; nasals 12 - 5 ; interorbital breadth 8'7 ; 

 least breadth across brain-case 16"5 ; bi-meatal breadth 2-4 ; 

 palatilar length 17" 7. Upper tooth-series (crowns) 7*2 ; 

 diagonal diameter of p 4 3 ; breadth across outer crowns of 

 p* 7-8. 



Hab. Southern part of Tucuman Province. Type and 

 three other specimens from Monteagudo, about 80 km. S.E. 

 of Tucuman City ; one specimen from La Madrid, 15 km. 

 further in the same direction. 



