Cavies in general, the more typical representatives of the Caviidae, are rodents with hooflike nails, four front and three hind toes, imperfect collar-bones, and the cheek-teeth divided by folds of enamel into transverse plates.
True cavies, or couies (Cavia), are best known by the guineapig, a domesticated and parti-coloured race derived from one of the wild species, all of which are uniformly coloured.
Cavies are widely distributed in South America, and are represented by several species.
As in the agoutis (Dasyproctidae), the milk-teeth are long retained,, while in the allied cavies (Caviidae) they are shed before birth.
The scapula is usually narrow, with a long acromion; the clavicles may be altogether absent or imperfect, as in porcupines, cavies and hares, but in most species are well developed.
In the family Caviidae, typified by the cavies (or guinea-pigs), may be included a large number of South and Central American rodents, among which the agoutis and pacas are often ranked as a family (Dasyproctidae) by themselves.
In the true cavies, or couies, Cavia, the foreand hind-limbs are short and of subequal length, the ears are short and there is no tail.
Of the remaining families of the Simplicidentata, all are southern, the cavies (Caviidae), chinchillas (Chinchillidae), and degus (Octodontidae) being Central and South American, while the Capromyidae are common to southern America and Africa, and the Ctenodactylidae are exclusively African.