146 SKETCH OF THE HISTORY OF MAMMALIA. 



ground to an elevation of two feet, descend on the spot 

 from which they rose. Their voice is a short, rather 

 sharp, phiintive pur. The individuals, male and female, 

 show great attachment to each other. They frequently 

 agitate their tails with a quick tremulous motion." Mr. 

 Bell observes that he had never before the arrival of 

 these individuals seen a specimen of the acouchi, nor 

 was he aware of the existence of even a preserved skin 

 in any English collection. It is the Olive Cavy of 

 Pennant. The general colour is olive mixed with 

 yellow and black : the hairs of the croup are not so 

 long as in the agoutis, and black. 



THE CAVIES (Fam. Cavida) 



Constitute a group (embracing the genera Cavia, Doli- 

 chotis, Kerodon, and Hydrochcerus) which is one of the 

 most distinctly marked in the class Rodentia, and which 

 should not be confounded with that of the pacas and 

 agoutis, the difference being very great, both as respects 

 the conformation of the skull and the characters of the 

 teeth. The molars, as seen in the teeth of the guinea- 

 pig or aperea {Cavia cobaia), Fig. 94, and of the ke?o- 

 do7i, Fig. 95, may be compared with those of the agouti, 

 Fig. 90, and the wide distinction will be at once appre- 

 ciated 



4—4 

 The molars are , lamellose, and composite ; the 



4—4 ' ^ ' 



folds of enamel enclose triangular or cordiform inter- 

 spaces. A projecting ridge always occurs on the outer 

 side of the ramus of the lower jaw. In the genus Cavia 

 the anterior feet have four toes, the posterior three ; the 

 nails are short and robust ; there is no tail. As an ex- 

 ample of this genus we may take the common guinea- 

 pig, or aperea, the domestic descendant of a species still 

 common in a wild state in various parts of South America. 

 Mr. Darwin, who met with the wild aperea abundantly, 

 states it to be "exceedingly common in the neighbour- 

 hood of the several towns which stand on the banks of 

 the Rio Plata. It frequents different kinds of stations, 



