47C 31 r. U. Thomas on new 



^'ize about a5 \n A. cineren. Fur similarly soft and iiiu', 

 liairs of back about 17 mm. in leutjtii. Geiioral colour above 

 near Ridgway's " drab," very uniform everywhere, the back 

 little darker tiian the sides. Under surface greyish drab, the 

 liairs broadly slaty for three-fourths their length, their tips 

 pale drab ; hairs of sternal gland white to their roots. Chin 

 greyish white ; underside of neck stronger drab. Head 

 Avitliout special niarkitigs. Hands and feet i)ure white, the 

 latter of more normal length than in the curiously short-footed 

 A. cinerea. Tail of medium length, iron-grey above, white 

 below. 



Skull agreeing with that of A. cinerea in the normal 

 minuteness and separation from each other of the posterior 

 })alatal foramina, as in the majority of rodents, while in 

 A. henncttii and murrayi these are of exceptional size and arc 

 fused into a single median foramen. Nasals markedly nai'- 

 rowed and pointed posteriorly. I^Ialars not much expandei!, 

 but differing from others by being so twisted that, instead of 

 forming a nearly vertical jdate, their inner side can be broadly 

 seen from above, facing upwards and inwards towards tlie 

 supraorbital edges. Interorbital region very narrow, more 

 so than in any other s|)ecies. Biillic smaller than in either 

 A. murrayi or cinerea. 



Incisors not so reduced as in A. cinerea^ about as in 

 A. bennettii. JMolars of the usual pattern. 



Dimensions of the type : — 



Head and body 201 mm.; tail 144; hind foot 31; 

 ear 21-2. 



Skull : greatest length 50 ; condylo-incisive length 47 ; 

 zygomatic breadth 24*5; nasals 20"5 x 5"5 ; interorbital 

 breadth 6*4; least breadth across brain-case 20; ])alatil!ir 

 length 22; diagonal length of bulla 16'2; bimeatal breadth 

 25; upper clieek-tooth series (crowns) 10*2; dental length 

 2G-6. 



Ilah. Otro Corro, Catamarca. Alt. 3000 m. 



Type. Adult male. B.M. no. 20. 3. 17. 62. Original 

 iiuniber 817. Collected 15th November, IDID, by E. Budin. 

 lour specimens. 



" Caught among rocks, in the clefts of which it lives." — 

 E. B. 



This fine chinchilla-rat, as Sr. Budin calls it, adds to the 

 genus Ahroco7na a fourth aiul very distinct s[)ecies, readily 

 tlistinguishabic externally by its colour and proportions, and 

 craniall}' by its narrow interorbital region, small posterior 

 palatal foramina, and the other characters above detailed. 



