Sub-Fam. 10. Neotominae.—The last sub-family of the Muridae is that of the Neotominae, containing the North American genera Neotoma, Xenomys, Hodomys, and Nelsonia.
Fam. 3. Bathyergidae.—This family contains several genera which consist of subterranean forms. All these Rodents agree in a number of characters, of which the principal are as follows:—
The eyes are very small, and the external ears are reduced to the merest fringe of skin round the aural aperture. The legs are short, as is the tail; the hair-covering is reduced—a reduction which finds its culmination in the nearly nude Heterocephalus. Being burrowing creatures, a number of other modifications in accordance with this mode of life are to be seen in their structure. The upper incisors stand out in front of the closed lips, and prevent the entrance of earth. For the same reason
the nostrils are small, and the forehead but little expanded between them.
The genus Bathyergus contains but a single species, the Cape Mole-Rat, which is found in Southern Africa; it is of moderate size, not exceeding a small Rabbit in dimensions. On the fore-limbs are exceedingly long claws, of which that borne by the second finger is the longest, and the claw of the thumb the shortest. The hind-feet have by no means such long claws. The scratching and burrowing is naturally chiefly effected by the fore-limbs. The small and large intestines are of equal length, and each is rather more than six times the length of the caecum; in these measurements the present genus differs from the next.
Georhychus.—Of this African genus there are about ten species. The claws are not so long as in the last genus, but there are, as in Bathyergus, four molar teeth on each half of each jaw. The intestinal measurements in an example of G. capensis were: small intestine, 25 inches; caecum, 4 inches; large intestine, 15 inches.
The genus Myoscalops or Heliphohius (also with an African range) has six back teeth on each side. A number of species sometimes referred to the last genus are placed here by Mr. Thomas. The claws are small.
One of the most remarkable genera of this family is the little Heterocephalus from Abyssinia and Somaliland. As Mr. Thomas justly remarks,[[337]] it "is a peculiar-looking little creature, about the size of the Common Mouse, but looking almost more like a tiny hairless puppy on account of its nearly naked skin, small eyes, and peculiar physiognomy." Though apparently naked, there are numerous scattered hairs over the entire body, and the toes are fringed with stiffish hairs, which must be advantageous to a burrowing animal. There are two species, H. glaber (originally described by Rüppell), and H. phillipsii, of which our knowledge is due to Mr. Thomas. The length of the entire creature including the tail is not more than 134 mm., both species being approximately of the same dimensions. Mr. Lort Phillips, the discoverer of the species which bears his name, writes "that this little creature, called 'Farumfer' by the Somali, throws up in places groups of miniature craters, which exactly resemble volcanoes in active eruption. When the little beasts were at
work, I used frequently to watch them, and found that the loose earth from their excavations was brought to the bottom of the crater, and sent with great force into the air in a succession of rapid jerks, and that they themselves never ventured forth from the shelter of the burrows."[[338]]
Fam. 4. Spalacidae.—"The Spalacidae," observes Dr. Blanford, "are sometimes called rodent moles, and resemble a mole in general aspect, having cylindrical bodies, short limbs, small eyes and ears, large claws, and a short or rudimentary tail." The existence of a spiral valve in the caecum may perhaps characterise this family; but it has at present only been found in the two genera Spalax and Rhizomys.