The Pouched Rats, or Pocket Gophers, and the Pouched Mice of North America, constitute a family distinguished from all the preceding forms by the presence of a pair of great cheek-pouches, opening _outside_ and not inside the mouth (_see_ figure). These cheek-pouches are hairy inside throughout. The angular portion of the lower jaw is strongly twisted, the molars are four in number on each side in each jaw, and the squamosal bone is very large. In external characters the animals of this family present considerable diversity, which has led to their being divided into two well-marked sub-families, the distinctive peculiarities of which are of such importance that Dr. Coues has raised them to the rank of distinct families. The GEOMYINÆ, or Pouched Rats, are more or less Rat-like animals, in which the feet are five-toed, and all the toes furnished with claws, those of the fore feet being very strongly developed; and the tail is short. Certain other characters are presented by the skull. The outline of this part, including the zygomatic arches, is almost quadrangular; the infra-orbital opening is far in front of the jugal process; the malar bone extends forward to the lachrymal. [Illustration: MOLAR TEETH OF THE MEXICAN POUCHED RAT.] [Illustration: UNDER SURFACE OF THE HEAD OF HETEROMYS.] 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. [Illustration: SKULL OF THE MEXICAN POUCHED RAT.]