Other African forms constitute the small sub-family of the TREE MICE (Dendromyinæ), which are entirely confined to the southern portion of the continent. They are characterised by having the incisors rounded and grooved in front, the infra-orbital opening not narrow below, and the coronoid process of the lower jaw very small. The ears are clothed with hairs; and the feet, which are five-toed, are furnished with long claws, which are serviceable to the little rat-like animals in climbing up the trunks of trees. The BLACK-STREAKED TREE MOUSE (Dendromys mesomelas) is a rather pretty little species, of a greyish colour, with a black line down the middle of the back. It is slender in form, with a long, scaly tail, rounded ears, and the two outer toes in each foot shorter than the rest. Steatomys pratensis, from Mozambique, is stouter in form than the preceding, and has a short, densely hairy tail; and in Lophuromys ater, from the same locality, the incisors are not grooved, and the fur is developed into fine flattened bristles.
The GERBILLES (Gerbillinæ) are distinguished from all other Muridæ (although approached by Hapalotis) by the great length of the hind limbs, which are converted into powerful leaping organs, somewhat as in the Jerboas and Kangaroos, although not quite to the same extent. Like all the preceding forms, they have the molars furnished with roots, but not with tuberculate crowns, these being divided into transverse plates formed by separate elliptical or rhomboidal coats of enamel. The incisor teeth are narrow, the infra-orbital opening as in the Murinæ, and the tail long and hairy. The Gerbilles are plump little animals, with a short neck, a broad head, and a pointed muzzle. The feet are five-toed, but the thumb on the fore feet is reduced to a mere wart-like process with a flat nail. They are confined to the Eastern hemisphere, and, indeed, to the African continent, the south of Asia, as far as India, and the south-east of Europe, where they live both in cultivated districts and in the driest deserts, and often occur in great numbers, when they may cause considerable damage to the neighbouring crops. They shelter themselves during the day in shallow burrows, and come forth in the evening in search of their food, which consists chiefly of grain and roots. They store up great quantities of the ears of corn in their subterranean dwellings, and in many places the poorer inhabitants search after these stores, and by digging them out procure a good supply of grain. They are very prolific, the females producing large families several times in the year.
MOLAR TEETH OF THE GERBILLE.
Several other forms of Muridæ, with rooted molars, have been distinguished, and all are inhabitants of the Eastern hemisphere. The genera Phlœomys and Nesokia, each including a single species, form the group PHLÆOMYINÆ, characterised by having broad incisors and the molars divided by transverse plates of enamel. The characters of the skull are as in the Murinæ. Phlœomys Cumingii is from the Philippine Islands; Nesokia Griffithii inhabits Northern India. Platacanthomys lasiurus, the only known species of the group PLATACANTHOMYINÆ, resembles a Dormouse in its form, and is nearly allied to the preceding species, but has the fur of its back mixed with long, flattened, bristle-like spines. It is a native of the Malabar coast.
SKULL OF THE WATER-MOUSE.
The WATER MICE (Hydromyinæ) are of particular interest, as being a small group, exclusively confined to the Australian region, and presenting the exceptional character among the Rodents of having only two molars on each side in each jaw. These teeth, are rooted, and divided into transverse lobes by ovate enamel lobes; the front tooth is much larger than its fellow. The Hydromys are small rat-like animals of slender form, with long tails, rather densely clothed with short hairs, and short limbs. The hind feet have much stronger claws than the fore feet, and their toes are partially webbed. Five species of this group are known from Australia and Van Diemen’s Land, where they inhabit the banks of the streams. The best known are the Yellow-bellied and the White-bellied Water Mice (Hydromys chrysogaster and leucogaster), both of which inhabit New South Wales, and the latter is also found in Van Diemen’s Land. The Sooty Water Mouse (H. fuliginosus) is an inhabitant of Western Australia.
In the SMINTHINÆ—a group which includes only the genus Sminthus, founded for the reception of a rat-like Rodent (S. vagus) first discovered in the Crimea, but now known to range from Hungary, Finland, and Sweden, through Russia to the banks of the Irtisch and Yenisei, and into Tartary (Bokhara)—we find another exceptional character of the molar teeth. There are four of these teeth on each side both above and below, the first and fourth of which are much smaller than the intervening ones. In this animal the ears are rather long and pointed, the legs are rather short, and the tail is about as long as the body, and clothed with short hairs.
