152 Mr. O. Thomas on 



XI. — Notes on the Species of the Genus Cavia. 

 Bj Oldfield Thomas. 



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



The genus Cavia ranges from Venezuela and Guiana in fhe 

 nortli of South America to the pampas of Buenos Ayres 

 in the south, and extends across the whole breadth of the 

 continent, from Peru to Pernambuco. 



Any examination of the species that exist in this area, and 

 tlieir correct names, has been rendered very dijfficult by the 

 occurrence of such widely different specimens in the same 

 areas, on which account I have long hesitated to attempt to 

 work out this puzzling group. Definite cranial characters 

 seemed almost non-existent, and one appeared to be reduced 

 to distinguishing the local forms purely by average differ- 

 ences of size and shades of colour in a group where there is 

 not a great range in either. 



On taking up the subject afresh, however, I find that one 

 character, observed by Lund in 1838, but overlooked ever 

 since, detinitely and sharply separates the smaller Brazilian 

 species from the larger ; and then, these smaller forms being 

 laid on one side, the whole problem immediately becomes 

 simplified. 



This character is the possession by Cavia fidgida, the 

 smaller Brazilian cavy, of a deep outer re-entrant angle or 

 notch at the front end of the ])Osterior lobe of vfi *, tliis angle 

 being quite shallow in the larger forms. This notch is so 

 deep and well defined that there is practically never any case 

 where one is doubtful as to the allocation of an individual 

 skull. 



When writing about the group in 1901 f, I recognized 

 Cavia fidgida (under the name of riifescens) by its smaller 

 size, but, not knowing of the tooth-character, I erroneously 

 made the small Argentine " quiso" a subspecies of it. Now, 

 however, it is evident that there is no special relationship 

 between the two. 



Taking first the ordinary species without the extra molar 

 notch, and going from north to south on the Eastern non- 

 Andean part of the continent, we have in Guiana 



• Figured bv Lund, K. Dansk. Vid. Selsk. viii. pi. yxv. fig. 15. 

 t Ann. & iNlag. Nat. Hist. (7) viii. pp. 532-534 (1901). 



