Eastern Buenos Ay res, fyc. 245 



11. Myocastor coypus, Mol. 

 <J. 2054, 2077, 2078 (juv.) ; ? . 2076. 



12. Lagostomus maximus, Blainv. 



<?. 2084; ?. 2101,2105. 



These are typical Argentine Viscachas, and agree with 

 other specimens from localities south of 30° S. latitude. 



But four examples from Tucuman differ from them in the 

 quality of their fur and in the structure of their palates, and 

 may be subspecitically separated as follows : — 



Lagostomus maximus immollis, subsp. n. 



Size a little larger than in true maximus. Fur compara- 

 tively harsh and coarse, with much less underfill",, especially 

 on the rump, where it is scarcely richer than on the rest of 

 the body. In maximus the rump is clothed with a thick coat 

 of woolly underfill" nearly 30 mm. in length. The specimens, 

 having been killed in September, would be in full winter 

 fur, while some of the woolliest specimens of maximus are in 

 summer fur (December). General colour a rather browner 

 grey than in maximus, but no stress can be laid on this. 



Skull like that of maximus, except that the palatal foramina 

 are distinctly broader (more than 3'6 mm. in breadth in all 

 specimens of immollis, less than 3*4 mm. in all of maximus) 

 and distinct incisive foramina are always present, 1*6 mm. in 

 breadth or more, these being commonly absent or quite minute 

 in maximus. 



Dimensions of the type (measured in flesh) : — 



Head and body 470 mm.; tail 180 ; hind foot 130; ear 55. 



Skull: condylo-basal length 1145 ; greatest breadth 73; 

 nasals 54*5 X 21 ; breadth between outer corners of anteorbital 

 foramina 54; least interorbital breadth 32 ; front of parietals 

 to back of occipital crest 31*5 ; breadth of incisive foramen 1'7 ; 

 palatal foramina 12"6 x 4"7 ; length of upper molar series 

 (crowns) 26*5. 



Bab. Tapia, Tucuman. Alt. 700 m. 



Type. Adult male. B.M. no. 3. 6. 6. 11. Original num- 

 ber 1875. Collected 17th September, 1902, by L. Dinelli. 

 Presented by Oldfield Thomas. Four specimens. 



Furthermore the Museum contains the skull of a Lago- 

 stomus which was obtained in Peru by Mr. Kalinowski, by 

 whom it was found buried in sand. 



No Viscachas of this genus are known to live in Peru, and 



