159 Zoological Society, 



sit is, attritu complanatis. America Australis incolae, gregarii, 

 subterranei, mites. Artus postici anterioribus subduplo longi- 

 oribus. Cauda producta, ad apicem superneque longe setosa. 



Gen 1. Lagotis. 

 Dentes incisores -§- acutati -, molares *^-J, singuli e lamellis tribits com. 

 pletis obliqais constantes. Cranium postice superneque areuatum t 

 tympani cellulis superioribus inconspicuis. Pedes omnes tetra- 

 dactyli, pollice omnino deficienle, unguibus parvis subfalcularibus. 

 Auriculce longissimce. Cauda longa. Rupicolae (Peruviani) 

 vellere molli caduco induti. 



Lagotis Cuvieki. 



Gen. 2. Chinchilla. 



Dentes incisores %- acutati- molares ~, singuli e lamellis tribus com- 



2 4— 4 7 O 



pletis obliquis constantes, prceter anticum inferiorcm bilamellosum 

 lamelld anteriore prqfunde bilobcl. Cranium postice retuso-lrun- 

 catum, super ne depresso-complanatum, tympani cellulis conspicue 

 infiatis. Pedes antici pentadactyli, pollice completo ; postici te- 

 tradactyli, unguibus parvis subfalcularibus. Auriculce amplce. 

 Cauda longiuscula. Rupicolae Chilenses et Peruviani, veJiere 

 mollissimo tenacissimo induti. 



1. Chinchilla lanigera, Benn. 



2? Chinchilla aurea. 



Callomys aureus, Isid. Geoffr. St. Hil. in Ann. Sci. Nat. 

 torn. 21, p. 291. 



Gen. 3. Lagostomus. 

 Dentes incisores -f- acutati: molares \— A , singuli e lamellis binis com- 



2 7 4—4' p 



pletis obliquis constantes, postico superiore trilamelloso. Pedes 

 antici tetradactyli, pollice omnino deficiente, unguibus parvis fal- 

 cularibus ; postici tridactyli, unguibus productis rectis robustis. 

 Auriculce mediocres. Cauda mediocris. Campestres Bonarienses 

 et Paraguaienses, vellere parum utili induti. 

 Lagostomus trichodactylus, Brookes. 



In the Lagotis Cuvieri the fore feet, like the hinder, have only 

 four toes, there being no vestige of a thumb; and the claws are 

 small, slightly sharpened, and entirely concealed by long and some- 

 what bristly hairs. Those of the hinder feet are similar in shape 

 and rather larger; but that of the inner toe is flattened, curved in- 

 wards, and exposed, the hairs immediately adjoining it giving place 

 to a tuft of about eight rows of short, stiff, horny, curved bristles, ap- 

 proaching nearly in their rigidity to the comb-like appendage, which 

 is found in almost the same situation in the Ctenodactylus Massonii, 

 Gray. A similar structure also occurs in the Chinchilla. 



Mr. Bennett afterwards entered at length into the internal ana- 

 tomy of Lagotis and Chinchilla, and gave a full description of their 

 skeletons, dwelling more particularly on the points of difference ex- 

 isting between them. He concluded by some observations on the 



