The subfamilies Cricetinae and Microtinae contain the Ham sters and Voles respectively; the former group which has a Murine dentition, the molars being rooted, is found over America, S.E. and Central Europe, Central Asia and Southern Africa; the African representative is the genus Mystromys. The typical genus Cricetus, contains the well-known Hamster of Europe and Asia Minor. A large number of American genera is included in this subfamily. The members of the Microtinae, which contains the Lemmings and Voles, are distinguished by their prismatic, hypsodont or rootless, flat-crowned molars; a numerous group distributed over both hemispheres.
Spalacidae, mole-like animals, modified for a subterranean life; found over South Eastern Europe, Asia and Africa. The typical genus, Spa/ax, contains the Blind Moles of Europe, which extend into Egypt and western Asia. The Bamboo Rats of India, etc., fall into three genera, Nyctocleptes and Rhizomys, being very large (head and body 386 mm.) forms, and Cannomys, a smaller group from Siam, Burma and Bhutan. In Africa there is the closely allied genus Tachyoryctes, medium-sized moles with very soft, usually rufous-coloured fur. The American Pocket-Gophers (Geomys and Thomomys) form the family Geomyidae. The Kangaroo-Rats of the New World, Dipodomys, Perodipus and Microdipodops, form with the genus Heteromys, from Colombia. and Venezuela, the family Heteromyidae. Another group of bur rowing mole-like rodents is the Bathyergidae which is confined to Africa ; including Heterocephalus, the naked moles of East Africa; and the genus Cryptomys which is found over a great part of the continent. The Jaculidae have the body modified for jumping, the tail being long and plumed and the hind-feet large ; the fore-limbs are usually much reduced in size. This family contains three sub families:—(i ) Sicistinae, found in the eastern hemisphere, west as far as Norway; small mouse-like animals, with long tails and feet, and a black dorsal stripe. (2) Jaculina,e, the Jerboas, confined to the Palaearctic and Ethiopian Regions, distinguished by their very elongated hind-feet ; several genera can be distinguished; Jaculus includes the 3-toed forms, the majority of the forms com ing from Northern Africa; Alactaga is a closely allied genus which spreads as far north as Southern Russia. (3) Zapodinae, in which the American members of this family are grouped.
Family Pedetidae, the Jumping Hares of Africa. This group is very difficult to classify, but on the whole it seems best to place it in the present section rather than with the Myormorpha. The molars are rootless and the hind-limbs elongated. The general dimensions are large, the body being about the size of a hare's. The next family, the Ctenodactylidae, includes four curious genera :—Ctenodactylus, the Gundis of Algeria and Tunis, small, thickset animals with very short tails and pale buff in colour; Massoutiera, the long-tailed Gundis of N.W. Africa; Pectinator,
a very similar animal but with a longer, more bushy tail, from Somaliland; and Petromys, the Rock Rat, of S.W. Africa. The Capromyidae contains the African Cane-Rats (Thryonomys) and the West Indian genus of arboreal forms known as Capromys. The South American Coypu (Myocastor) is also sometimes placed in this family, sometimes in a separate group altogether. In this genus the incisors are very large, the tail fairly long and naked, and the hind feet webbed. In the true Porcupines (Hystricidae) the skull is greatly inflated and the tail short; the typical genus Hystrix inhabits the greater part of Africa and the Mediterranean region of Europe. The Indian and other Asiatic porcupines related to Hystrix are now considered to represent a distinct genus, Acan t/iion. The Brush-tailed Porcupines of the genus Atherurus, are common to both West Africa and Asia ; these porcupines are at once distinguished from the typical ones by the much longer, scaly tail which terminates in a brush of bristles. The porcupines of America are grouped together in the family Erithizontidae. The typical genus is represented by the Canadian Porcupine (E.
dorsalis) in which the tail is short, and the spines of the body are nearly hidden by a growth of long hair. Synetheres, from South and Central America, is a long and prehensile-tailed genus of Tree Porcupines.
In the South American family Chinchillidae there are two or three genera of terrestrial rodents with elongated hind-limbs, very soft fur, and bushy tails. The typical genus, Chinchilla, contains one species, C. lanigera, which provides the well-known Chin chilla fur; it is found only in the Peruvian and Chilian Andes. Almost equally soft is the fur of the much larger Viscachas (Viscaccia), animals about the size of a large rabbit, with long hind-feet, long, bushy tails, and bearing a median dark dorsal stripe down the back. The Paca (Coelogenys) and the Agoutis, of Central and South America, form another family, the Dasy proctidae; these animals are of large size with short or obsolete tails, and hoof-like claws. The Agoutis have slender limbs, with three hind toes, whereas the Paca has five hind toes and an enormously developed zygomatic region; the latter species is about two feet in length. The family Dinomyidae, represented by a single species from Peru, D. branicki, differs in having a long, bushy tail, cleft upper lip, and four digits on each foot. The family Caviidae is the las" of the Simplicidentata and contains about 7 different genera, one of them, Hydrochaerus, containing the largest existing rodent. This animal, the Capybara (H. capybara) is massively built and is about the size of a medium-sized pig (length of body 4 ft.). The body is covered in long, coarse hair, the feet are fully webbed, and the molars complex; the Capybara occurs only in South America. The Patagonian Cavy, Dolichotis patachonica is rather larger than a big rabbit, having very large ears and a short tail ; in general colour usually rufous. This beast inhabits the arid plains of Patagonia and La Plata. Lastly, the true Cavies (Cavia) are small tailless animals with short limbs and reduced ears ; they are entirely neotropical.