192 PHILOSOPHY OF ZOOLOGY. 



{b.) Roots of the grinders simple, prismatical. 

 Grinders three on each side in both Jaws. 



Tail compressed, scaly. 



77. FiBEB. Ondatra. Feet webbed. Tail long. Cas- 

 tor zibethicuSy Lin. Has much the habit of the beaver. 



Tail round and hairy. 



78. Arvicoi.a. Campagnol. Tail about half the 

 length of the body. Mus amphibius, Lin. 



79. Georychus. Leming, Tail and ears very short. 

 Toes formed for burrowing. This genus differs but little 

 from the preceding. M. Cuvier assigns to the former a 

 length of tail nearly equal to the body. In the A. amphi- 

 bius, he says, " La queue de la longueur du corps." In 

 the specimens of A. amphibius and A. agrestis, which 

 have come under our notice, the tail did not exceed one- 

 half of the length of the body. 



Grinders Jour on each side, in both Jaws- Clavicles im- 

 perfect. Caviadae. 

 Five fingers and toes. 



80. CiELOGENus. Immediately under the eye, in the 

 jaw, on each side, there is a remarkable slit or cavity Mus 

 pactra, Lin., or Spotted Cavy. 



Four fingers and three toes. 

 Feet webbed. 



81. Hydrochoerus. Capibara. Claws remarkably 

 large and strong. Cavia capibara, Gm. 



Feet simple. 



82. Chloromys. Agouti. With a tail. Mus aguti, 

 Lin. 



83. Cavia. Cavy. No tail. 



