“This animal, known by the name of Aperea, is exceedingly common in the neighbourhood of the several towns which stand on the banks of the Rio Plata. It frequents different kinds of stations,—such as hedge-rows made of the Agave and Opuntia, or sand hillocks, or again, marshy places covered with aquatic plants;—the latter appearing to be its favourite haunt. Where the soil is dry, it makes a burrow; but where otherwise, it lives concealed amidst the herbage. These animals generally come out to feed in the evening, and are then tame; but if the day be gloomy, they make their appearance in the morning. They are said to be very injurious to young trees. An old male killed at Maldonado, weighed 1 lb. 3 oz. In all the specimens I saw there, (during June, or winter,) I observed, that the hair was attached to the skin less firmly than in any other animal I remember to have seen.”—D. 2. CAVIA PATACHONICA. Cavia Patachonica, _Shaw_, General Zoology, vol. ii., part 1, p. 226. Dasyprocta Patachonica, _Desmarest_, Mamm. p. 358, Sp. 574. Dolichotis —— —— —— —— in Note, p. 359–360 Chloromys Patachonicus, _Lesson_, Manuel de Mammalogie, p. 301. Lièvre Pampa, _Azara_, Essais sur l’Histoire Naturelle des Quad. de la Province du Paraguay. French Translation, vol. ii. p. 51. In the form of the cranium, and in the structure of the teeth, this animal possesses all the characters of the Cavies (_Caviidæ_).[43] Habitat, Patagonia. “This animal is found only where the country has rather a desert character. It is a common feature in the landscape of Patagonia, to see in the distance two or three of these Cavies hopping one after another in a straight line over the gravelly plains, thinly clothed by a few thorny bushes and a withered herbage. Near the coast of the Atlantic, the northern limit of this species is formed by the Sierra Tapalguen, in latitude 37° 30′, where the plains rather suddenly become greener and more humid. The limit certainly depends on this change, since near Mendoza, (33° 30′.) four degrees further northward, where the country is very sterile, this animal again occurs. Azara erroneously supposed that its northern range was only 35°.[44] It is not clear on what circumstances its limit southward between Ports Desire and St. Julian (about 48° 30′.) depends; for there is in that part no change in the features of the country. It is, moreover, a singular circumstance, that although the Cavy was not seen at Port St. Julian during our voyage, yet Capt. Wood, in 1670, speaks of them as being numerous there. What cause can have altered, in a wide, uninhabited, and rarely visited country, the range of an animal like this?