Of the animals thus characterised, the Continent of North America possesses, according to Dr. Coues, seven species, and they are met with from Hudson’s Bay and the Columbia River in the north, as far south as Mexico. The best-known species, the COMMON POCKET GOPHER (Geomys bursarius), inhabits the whole valley of the Mississippi, and extends northwards into Canada. It reaches the foot of the Rocky Mountains in Colorado, but is not known to occur west of that range. It is also found in Texas. This Pouched Rat, like the rest of its genus, has the incisors broad and the upper ones deeply grooved; but in addition to the ordinary deep groove it has a fine line close to the inner margin of each of these teeth. Its form is stout and clumsy, but its coat is beautifully soft and velvety, like that of the Mole, but of a dull reddish-brown colour, with the feet and tail white. The average length of an adult specimen is from seven to eight inches, and the tail is two or three inches long. This organ is clothed with hair nearly to the tip.
SKULL OF THE MEXICAN POUCHED RAT.
Like the Mole, this animal lives in burrows, which it makes in all directions in the ground, throwing out as it proceeds heaps of earth, which exactly resemble ordinary mole-hills. To enable it to perform these labours the claws of the fore feet are exceedingly powerful; and to adapt it the better to its subterranean existence, the eyes are very small, and the external ears are wanting. Its digging operations have generally the same object as those of the Mole—namely, the search for food. The tunnel is carried along not far from the surface of the ground, and the roots of any plants that lie in its course are bitten off and devoured by the little miner. Besides the runs, the Pouched Rat digs himself a convenient dwelling in the shape of a chamber hollowed out under the roots of a tree, access to which is gained by a somewhat spiral descending passage. This chamber, which is usually at a depth of four or five feet, is comfortably lined with soft grass, and the nest in which the female brings forth her young is a cavity of the same kind, but surrounded by circular passages, from which, like that of the Mole, other passages branch off. One of these, according to Gesner, leads from the nest to a large store-chamber filled with nuts, seeds, and roots, among which the potato was found to play an important part. These provisions are carried to the store-house in the great cheek-pouches, which the animal is said to fill by the aid of its tongue, and to empty with the fore paws. This Pouched Rat does much damage in cultivated ground by attacking the roots of both plants and trees, sometimes destroying a great number of the latter in a few days. The female produces from five to seven young at the end of March or the beginning of April. The other species of Geomys closely resemble this in their habits.
Of the second genus belonging to this sub-family (Thomomys) Dr. Coues admits only two species, one of which, however, occurs under three named forms. They may be distinguished from the species of Geomys by their having the upper incisors plain, without grooves.
The NORTHERN POCKET GOPHER (Thomomys talpoides), with its sub-species, ranges over nearly the whole of North America from the Hudson’s Bay Territory to California and New Mexico. The three forms are for the most part in accordance with geographical distribution. A small species (Thomomys clusius) has been obtained in the Rocky Mountains.
The HETEROMYINÆ (forming the family Saccomyidæ of Dr. Coues, although he does not accept the genus Saccomys) are more slender and delicate in form than the Geomyinæ, and have the hind limbs and tail elongated, the former, indeed, being converted into leaping organs like those of the Jerboas and Kangaroos. The eyes and ears are larger, and the animals are in every respect adapted to life in the open, while the Geomyinæ, on the contrary, are subterranean in their habits. The hair in the present family is coarse and harsh, sometimes even spiny. In skeletal characters we find a similar alteration. The incisors are narrow; the skull is delicate, with its angles rounded off, and the mastoid bones form a considerable part of the roof of the cranial cavity; the zygomatic arches are slender; and, the lower root of the maxillary process being undeveloped, the infra-orbital opening is not defined. As in the Jerboas, the cervical vertebræ are sometimes anchylosed. Like the Geomyinæ, these animals are confined to America, and chiefly limited to the Southern United States and Central America, although some of the species occur as far north as the Columbia River and Hudson’s Bay, and one is found in Trinidad. By American writers they are called “Pocket Mice.”
PHILLIPS’S POCKET MOUSE, also known as the Kangaroo Rat (Dipodomys Phillipsii), is one of the best known species of this group. It is an elegantly formed little creature, about four inches long, with a slender tail nearly six inches in length. Its colour above is mouse-brown, white beneath; the sides of the body have some white streaks, especially one from the ear towards the shoulder, and one on the thigh running towards the root of the tail; the tip of the tail is also white. This is a Californian species, but extends throughout the Pacific region of the United States. It is represented in the Rocky Mountains by a rather larger and stouter form, with smaller ears and a shorter tail (Dipodomys Ordii), which is generally regarded as distinct, but is placed by Dr. Coues as a sub-species. The habits of the species are comparatively little known, but they appear to live in the most desert places they can find, the barren spots on which the only plants that seem to flourish are the great mis-shapen cactuses. They dwell in holes under rocks and stones, from which they emerge at sunset, and hop about gaily after the fashion of little Kangaroos. The places in which these Pocket Mice are found are so bare of vegetation and destitute of water, that it is difficult to imagine how they contrive to exist. In all probability they pick up a scanty living in the shape of roots and grasses, especially seeds, carrying a supply for the day into their holes in their great cheek-pouches.
The YELLOW POCKET MOUSE and the LEAST POCKET MOUSE (Cricetodipus flavus and parvus) are very minute creatures, only about two inches long in the head and body. The tail is longer than the head and body in the latter, shorter in the former species, and the colour of the fur in both is a pale buff. These species are found in the Rocky Mountains and the region west of that range to the Pacific, the latter being inhabited by the second of the above species. Several species of the genus Heteromys inhabit Central America, and one is found in the island of Trinidad. Nothing appears to be known of their habits.
From these we pass as by a natural transition to