FAMILY XV.—DINOMYIDÆ.
This family has been founded for the reception of a single species, of which only a single specimen has hitherto been obtained. It is described by Professor Peters under the name of Dinomys Branickii. In its external appearance it closely resembles the Paca (Cœlogenys paca), but may at once be distinguished from that animal by its possession of only four toes both before and behind. The ears are short and rounded; the upper lip deeply cleft; the incisors very broad; the molars four on each side, and divided into transverse plates by folds of enamel; the clavicles are imperfect; and the tail of moderate length and well clothed with hair. The animal, which inhabits the high mountain regions of Peru, is of the size of the Paca, or about two feet long, exclusive of the tail, which measures rather more than nine inches. Its general colour is grey, produced by the sprinkling of white among nearly black hairs; and on each side of the body are numerous large white spots, of which the upper ones nearly run together, so as to form two longitudinal bands. The extremity of the tail is black.
The only known example of this Rodent was obtained by M. Constantin Jelski at the Colonie Amable Maria, on the Montaña de Vitoc, in Peru, having been found at daybreak walking about the yard. It showed no fear of man, and was easily killed by a sword cut or two on the head. The species would appear to be rare, as the inhabitants of the neighbourhood were not acquainted with it. Of course nothing is known of its habits.
THE DINOMYS. (After Peters.)
The chief interest at present attaching to this animal, therefore, consists in its peculiar combination of characters. Externally, as already stated, it resembles the Paca, with which it also agrees in the S-like form of the nostrils, and in the structure of the limbs (except the number of toes). In the lamellar structure of the molar teeth, in the structure of the skull, and of the skeleton generally, and especially in the flattened form of the front of the sternum and the development of clavicles, it differs from the Paca and all other Rodents with hoof-like nails. In some minor particulars it resembles the Capybara. By the structure of the molar teeth and certain osteological characters, it is most nearly allied to the Chinchillas; while it approaches the genus Capromys among the Octodontidæ in the structure of the limbs and of some other parts of the skeleton. Professor Peters is evidently inclined to regard it as most nearly related to the Chinchillidæ, but as constituting a group establishing a closer union than previously existed between the families Chinchillidæ, Octodontidæ, Dasyproctidæ, and Caviidæ.
FAMILY XVI.—CAVIIDÆ (CAVIES).
This family, the last of the simple-toothed Rodents, includes a small number of species, of which the Common Guinea-pig may serve as a sort of type. The Guinea-pig is, however, one of the smaller species of the family, and is shorter in the limbs than most of its relatives. They have the incisor teeth short, that is to say, not extending far back in the jaw; the molars are rootless, variously divided by folds of enamel into lobes, the angles of which are acute; the palate is narrow in front, so that the upper series of molars approach each other rather closely in front; the clavicles are rudimentary or wanting; the fore limbs have four and the hind feet only three toes, all armed with hoof-like nails; the upper lip is not cleft; and the tail is rudimentary or wanting. They are stout, more or less rabbit-like animals, with a soft coat, and the ears variable in length; and they are confined to the continent of South America, where they chiefly inhabit the plains.
The RESTLESS CAVY (Cavia aperea), which is commonly regarded as the wild original of the so-called Guinea-pig (Cavia cobaya of some authors), is abundant on the banks of the Rio de la Plata, and extends thence northwards through Paraguay into Bolivia and Brazil. It is usually about nine inches long, with the fur of the upper part and sides of the body composed of a mixture of black and dingy yellow hairs, the chest greyish-brown, and the throat and belly pale dingy-yellow or brownish-grey. The incisor teeth are white. The genus to which this animal belongs may be at once distinguished from the other two genera constituting the family by the shortness of the limbs; the ears also are short; the feet are naked beneath; the hind toes are not webbed; and the molar teeth are nearly equal in size, and each composed of two angular lobes.
The specific name of the Restless Cavy seems to be derived from its popular name in the country where it occurs. According to Mr. Darwin, it is very common about the banks of the La Plata, sometimes frequenting sandy hillocks, and the hedge-rows formed of the agave and the prickly pear, but apparently preferring marshy places covered with aquatic plants. In dry places it makes a burrow; but when it frequents wet localities contents itself with the concealment afforded to it by the herbage. Rengger describes it also as generally haunting moist situations in Paraguay, and he adds that it keeps near the borders of forests, but is never found either in the forests or in the open fields. It lives in small societies of from six to fifteen individuals, in the impenetrable thickets of Bromelias, where its presence is revealed by the numerous beaten paths which it produces by going to and fro. In Bolivia, according to Mr. Bridges, it is peculiar to the low lands, and there takes shelter among the loose stones of the walls enclosing the fields. It is active in search of food early in the morning and in the evening, but will also come forth on gloomy days. Rengger and Azara both agree in the statement that the female produces only one or two young at a time; but the former says that this takes place only once in the year, whilst the latter describes the animal as breeding all the year round, and, indeed, in this way accounts for its abundance, notwithstanding its being preyed upon so extensively by rapacious birds and quadrupeds.