288 ZOOLOGICAL GARDENS. 
to the publication of the twelfth edition of his Systema, 
Linneus continued to refer not only the animal in 
question, but along with it the Cavy and the Agouti, 
to his comprehensive genus Mus. Klein was the first 
to break through the trammels of antiquity, and to 
form of the three animals just named a new genus 
under the name of Cavia, which was adopted by Gme- 
lin (who added to it the Capybara, erroneously asso- 
ciated by Linneus with the Hogs), and this designation 
has been retamed by most subsequent writers. 
But although these animals are closely connected 
together by many characters of the highest importance, 
and especially by the total want of clavicles, each of 
them is nevertheless distinguished from the rest by such 
striking peculiarities as fully to warrant its separation 
as a distinct genus. If we look to the teeth, we see at 
once that those of the Paca and Agouti are wholly 
unlike those of the Cavy and Capybara, and proceeding 
further in the examination we perceive minor but cha- 
racteristic differences in each of these subdivisions. In 
the feet and toes variations occur to a still greater 
extent ; and equal differences are found in other organs, 
both external and internal. We are therefore con- 
strained to acknowledge the justice of the subdivisions 
which this little family has undergone, although we 
cannot but regret the necessity of founding genera upon 
single species. There are now, however, recognised 
two distinct races of Paca, and three of Agouti; and 
it seems probable that further inquiry will make us 
acquainted with some additional species of each group. 
The dentary formula of the Pacas exhibits two inci- 
sors in each jaw, followed by a vacant space on either 
side, behind which are ranged four molars of nearly 
equal size, having the lines of enamel which are visible 
on their crowns disposed in an irregular and compli- 
