Page:EB1911 - Volume 23.djvu/467

Rh The hutia (Capromys pilorides) is nearly as large, arboreal in habits, and a native of Cuba, where it is the largest indigenous mammal. Other species occur in Cuba, Jamaica and the Bahamas, while a Venezuelan species, Procapromys geayi, represents a separate genus. In one kind the tail is prehensile. All these rodents are remarkable for the manner in which the liver is divided into minute lobules. Plagiodontia aedium, another member of the group, is peculiar to Hayti. The African cane-rats, Thryonomys (or Aulacodus), are large terrestrial rodents, ranging from the centre of the continent to the Cape, easily recognized by their deeply fluted incisors (see ). The Octodontidae, which are exclusively South American, differ from the preceding family by the tympanic bulla being filled with cellular bony tissue, and by the par-occipital process curving beneath it, while the cheek-teeth are almost or completely rootless and composed of parallel plates. The first front toe may be absent. The more typical members of the family are rat-like burrowing rodents, living in communities. The typical genus is represented by the degu (Octodon degus) and several nearly related species; other genera being Ctenomys, Octodontomys (Neoctodon), Aconaemys, Spalacopus and Abrocoma; the latter taking its name from its unusually soft fur. Among these, the tuco-tucos (Ctenomys) are characterized by their burrowing habits, almost rudimentary ears, small eyes, short tails and the kidney shaped grinding-surfaces of their cheek-teeth. They take their name of tuco-tuco from their cry, which resembles the blows of a hammer on an anvil, and may be heard all day as the little rodents move in their burrows, generally formed in sandy soil. In some districts the ground is undermined by these burrows, in which stores of food are accumulated. The species of Octodon have larger ears, longer, tufted tails and the sides of the cheek-teeth indented by plates of enamel; they are chiefly found in hedgerows and bushes, where they burrow. In Abrocoma the tail has no tuft, the ears are still larger and the lower cheek-teeth more complex than the upper ones. Aconaemys is an allied Chilean genus in which the enamel-folds meet across the molars. Several of these rodents live in the Andes, where the ground is covered for months with snow. The second group of the family is formed by the genera Loncheres, Dactylomys, Echi[no]mys, Proechimys and a few others, the members of which are rat-like rodents, with long scaly or furry tails, and frequently flattened spines mingled with the fur of the back. Most species are brown above and whitish beneath, but in some the lighter tints extend on to the sides, shoulders and head, communicating a coloration somewhat like that of a guinea-pig (see ). The North African gundis (Ctenodactylus gundi and Ct. vali) are the types of an African family, which also includes the genera Massoutiera, Peclinator and Petromys. In the gundi the two inner toes of the hind-foot are furnished with a horny comb and bristles for the purpose of cleaning the fur, and the tail is very short; but in Pectinator the tail is longer. Petromys has a still longer and more bushy tail, and no comb to the hind-feet. The gundi is a diurnal species, inhabiting rocky districts, and having habits very similar to those of a jerboa. Of these Ctenodactylus and Pectinator are characterized by the union of the incus and malleus of the internal ear, the free fibula and the almost rootless cheek-teeth. The premolar is very small, thus showing an approximation to the Myoidea, although in other respects Petromys appears to approximate to the Hystricidae.

Picas and Hares.—The remaining rodents, which include two families—the picas (Ochotonidae) and the hares and rabbits (Leporidae)—constitute a second sub-order, the Duplicidentata, differing from all the foregoing groups in possessing two pairs of incisors in the upper jaw (of which the second is small, and placed directly behind the large first pair), the enamel of which extends round to their posterior surfaces. At birth there are three pairs of incisors, but the outer one is soon lost. The incisive foramina are large and usually confluent; the bony palate is very narrow from before backwards; there is no alisphenoid canal; the fibula is welded to the tibia, and articulates with the calcaneum; and the testes are permanently external. All are terrestrial, and in many cases burrowing, in their habits, and some of them are of extreme fleetness. The Ochotonidae are represented at the present day only by the single genus Ochotona (Lagomys), which includes all the picas, or mouse-hares. They are small rodents with complete clavicles, fore- and hind-limbs of nearly equal length, no external tails and short ears. Skull depressed, frontals contracted and without post-orbital processes; p. or ; molars rootless, with transverse enamel-folds. In some cases the molar-formula is. The genus includes about a score of species of guinea-pig-like animals, inhabiting chiefly the mountainous parts of Northern Asia (from 11,000 to 14,000 ft.), one species only being known from South-east Europe and several from the Rocky Mountains and Alaska.

From the picas the hares and rabbits (Leporidae) are distinguished by the imperfect clavicles, the more or less elongated hind-limbs, short recurved tail (absent in one case) and generally long ears. The skull is compressed, with large wing-shaped post-orbital processes (fig. 16); p. . With the exception of Australasia, the family has a cosmopolitan distribution; and its numerous species resemble one another more or less closely in general external

characters. In all the fore-limbs have five and the hind four digits; and the soles of the feet are densely clothed with hairs 16.—Skull of the Common Hare (Lepus europaeus). similar to those covering the legs; the inner surface of the, cheeks being hairy. Although the family has such a wide distribution, the greater number of the species are restricted to Europe, northern and central Asia and North America; South America having very few. Till within the last few years the majority of naturalists followed the practice of including all the members of the family in the genus Lepus. It is true that Mr E. Blyth long ago proposed the name Caprolagus for the remarkable spiny rabbit of the western Himalayas, while the generic name Oryctolagus was suggested later for the rabbit, and Sylvilagus for the American “cotton-tails”; but none of these was accorded general acceptation. Of late years, however, zoologists have come to the conclusion that generic subdivisions of the Leporidae are advisable. In 1899 Dr Forsyth Major proposed a classification of the family in which a number of species were grouped with the spiny rabbit in the genus Caprolagus, whilst Oryctolagus was taken to include not only the common rabbit, but likewise the Cape hare. A more recent classification is that of Mr M. W. Lyon, in which by far the largest number of species of the family are retained in the original genus Lepus, which has also the widest geographical distribution of all the genera. It is typified by the blue hare (Lepus timidus), next to which comes the common hare (L. europaeus) and certain other allied forms. The jackass-hares of Mexico, &c., such as L. californicus, form a second sub-group; while these are in turn followed by the American hare (L. americanus) and its immediate relatives. The cotton-tails, or wood-rabbits, of North and South America are regarded as forming a genus, Sylvilagus, by themselves, which includes the Brazilian and Paraguay hares, and appears to be chiefly distinguished by a certain feature in the parietal region of the skull. Under the name of Oryctolagus cuniculus, the rabbit is considered to represent a genus by itself, specially characterized by the shortness of the ears and hind-feet. The swamp-rabbit (L. palustris) and water-hare (L. aquaticus) of the southern United States form the group Limnotragus, characterized by the harsher fur, the shorter ears, tail and hind-feet, and the complete fusion of the post-orbital process (which is so distinct in the typical hares) with the adjacent parts of the skull, so that neither notches nor perforations are developed in this region. The short-tailed rabbit of the western United States (Brachylagus idahoensis) is the sole member of a group allied in general characters to the typical Lepus, but distinguished by the unusually short tail. Another group is Pronolagus, typified by the Cape thick-tailed hare, the so-called Lepus crassicaudatus, which is externally similar to Lepus proper, but has the skull and teeth of the general type of the next group. The tailless rabbit of Mount Popocatepetl, Mexico, originally described as a distinct generic type, under the name of Romerolagus nelsoni, is broadly distinguished by the entire absence of the tail, and the short ears and hind-feet, its general form being like that of the Liu-Kiu rabbit, while, as in the latter, the post-orbital process of the skull is small, and represented only by the hinder half. Next come three remarkable rabbits from the Indo-Malay countries, all closely allied, although regarded as representing three generic groups, Nesolagus, Caprolagus and Pentalagus. In all three the skull is of the type of Romerolagus. The first is represented by the Sumatran rabbit, the so-called N. netscheri, which apparently differs from the spiny rabbit mainly by the pattern of the cheek-teeth. The spiny rabbit, separated from Lepus by Blyth in 1845 under the name of Caprolagus hispidus, is an inhabitant of Assam and the adjacent districts, and distinguished by its harsh, bristly fur and short ears and tail. In the Liu-Kiu rabbit (Pentalagus furnessi) the coat is equally harsh, but the ears and hind-feet are shorter, and there are only five (in place of the usual six) pairs of upper cheek-teeth. In the loss of the last upper molar, the Liu-Kiu rabbit approximates to the picas, as does the tailless rabbit in the abortion of its caudal appendage. Mr Lyon's scheme seems to be the best attempt to explain the affinities of the members of the group. Whether all his genera be adopted, or all the species be included in Lepus, must largely be a matter of individual opinion.