RODENTIA. 157 



The fossil bones of an unknown species of Lagomys have been 

 discovered in the osseous breccia of Corsica. Cuv. Oss. Foss. 

 IV, p. 199. 

 After the two genera of Porcupines and Hares, come the Roden- 

 tia, united by Linnaeus and Pallas, under the name of Cavia ; but to 

 which it is impossible to affix any other common and positive cha- 

 racter than that of their imperfect clavicles, although the species of 

 which they are composed are very analogous to each other, both in 

 body and habits. They are all from the western continent. 



HydrochceruSj Erxleb. 



Four toes before and three behind, all armed with large nails, and 

 united by membranes ; four grinders throughout, of which the pos- 

 terior are the longest, and composed of numerous, simple and paral- 

 lel lamina ; the anterior laminae, forked towards the external edge 

 in the upper, and towards the internal one in the lower teeth. Only 

 one species is known, the 



H. capyhara; Cavia capyhara^'L.', Capyhara, Marcg. ; Capiy- 

 goiia, Azzar.; Cabiai, Buff. XII, xlix. (The Capyhara.) Size of 

 Siam Pig ; the muzzle very thick ; legs short; hair coarse, and 

 of a yellowish brown ; no tail. Inhabits the rivers of Guiana 

 and the Amazon, where it lives in troops. The Beaver only 

 approaches it in size. 



Cavia^ Illig. AncemAj Fr. Cuv. 



The Cobayes, or Guinea-Pigs, are miniature representations of the 

 Cabiais ; but their toes are separated, and each of their molars has 

 only one simple lamina, and one that is forked on the outside in the 

 upper ones, and on the inside in the lower. The species best 

 known, 



C. cobaia, Pall.; 3Ius })orcellus,L.', Buff. VIII, i, (The Gui- 

 nea-Pig) is now very common in Europe and America, where 

 it is brought up in houses, because its odour is thought to 

 drive away Rats, Like all domesticated animals, it varies in 

 colour. There is reason for believing it proceeds from an 

 American animal called Jlpcrea, which is of the same size and 

 form, but with a uniform reddish-grey fur. It is found in the 

 woods of Brazil and Paraguay. 



Kerodon, Fred. Cuv. 



The Mocos have rather simpler grinders than the Cobayes, each 

 being formed of two triangular prisms. 



