Spalax has inconspicuous eyes and external ears. The tail is totally absent. The lower incisors are more developed than in other Rodents; they project in a bony sheath beyond the posterior end of the ramus of the lower jaw. The scapula is long and narrow. The large intestine is half the length of the small intestine. The animal seems to have only two pairs of teats, one pectoral the other inguinal.
Spalax typhlus of Egypt, which is probably not different from the European form, makes extensive burrows, some of the branches being even 30 to 40 yards in length. In a "domical chamber," situated along the course of one of these burrows, Dr. Anderson found no less than 68 bulbs stored up. Its eyes are mere black specks among the muscles, but they appear, however, to have a proper organisation. There are altogether eight species of the genus, which is entirely Palaearctic in its range.
The genus Rhizomys, including a number of species known as Bamboo Rats, is purely Oriental in range. Rh. sumatrensis reaches a length of 19 inches; the better-known species, Rh. badius, is at most only 9 inches in length—in both cases the measurements are exclusive of the tail, which is a quarter to one-third of the length of the body, and is not scaly but nearly naked, with a few scattered hairs. The molars are three, and the incisors usually orange in colour; but sometimes the upper incisors are white as in Rh. badius. There are thirteen dorsal vertebrae. In Rh. pruinosus the large intestine is considerably longer than the small intestine; the lengths of the two sections of the gut are 42 and 30 inches respectively. In another
species the large intestine is slightly shorter than the small intestine. In Rh. badius the two parts of the gut are almost exactly equal in length. There are three pairs of inguinal and two pairs of pectoral teats. The name Rhizomys appears to have been given to the animals of this genus for the reason that they feed largely on roots. They burrow, and, like many other burrowing animals, feed in the evening. As is the case with other forms, Rhizomys is said to burrow with the assistance of its teeth as well as of its claws.
Fig. 237.—Bamboo Rat. Rhizomys badius. × ¼.
Tachyoryctes is an African genus closely allied to the last. There are three Ethiopian species. It is mainly to be distinguished by the different pattern upon the grinding surface of the molars.
Fam. 5. Geomyidae.—This family of burrowing Rodents is limited to North and Central America. The animals have cheek pouches, and small eyes and ears, in accordance with their mode of life. The claws of the fore-limbs are very strongly developed.
The genus Geomys contains some eight species, which are Central and North American, not extending, however, far north. The incisors of the upper jaw are grooved with two grooves. There are three pairs of teats—one axillary, and the two remaining inguinal.
Thomomys, without grooves on the incisors, reaches to Canada in the north, and does not extend as far south as the last genus.