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 has but a single enamel fold, whereas in Cannabateomys these teeth have several enamel folds. The tail, moreover, is but slightly hairy.

Loncheres with eighteen species is another Neotropical genus allied to the foregoing. Small spines are, as in many of these genera, intermingled with the fur. This genus has as many as seventeen dorsal vertebrae, which is an unusually large number. L. guianae is known as the "Porcupine Rat." Allied genera, also South American, and without spines in their fur, are Mesomys, Cercomys, and Carterodon.

The South American Thrinacodus is also known by one species, T. albicauda, which has rather more than the distal half of the long tail of a white colour. The fore-feet have four toes. The ears are broad and short.

'''Sub-Fam. 3. Capromyinae.'—A third sub-family of the Octodontidae is formed by the genera Myocastor, Capromys, Plagiodontia, and Thrynomys'', which are all Neotropical forms with the exception of the last, which is African.

Thrynomys (better known perhaps as Aulacodus) is a genus of African Rodent, containing some four species. The best-known of these is T. swindernianus, the Ground-Rat of West and South Africa. Its structure has been investigated by Garrod, by Tullberg, and by myself. The fur is mingled with flattish bristles; the tail is moderately long, about half as long as the body. The fore-feet are five-toed, but the two toes at each end of the series are quite small. The hind-feet are only four-toed, the hallux being absent. The claws of the hind-feet are stronger than those of the fore-feet. The ears are not long. The limbs are decidedly short, hence the name of "Ground-Pig" sometimes applied to this animal. The molars are four in number in both jaws. The incisors of the upper jaw are twice grooved. There are thirteen dorsal vertebrae. The length of the small intestine is 60½ inches, that of the large 49; the caecum is short, being only 8 inches long. It is a remarkable fact that the acromion is joined to the rest of the spine of the scapula by a joint.

Myocastor, a name which seems to have the rights of priority over the more familiar Myopotamus, applies to a large South American aquatic Rodent. The general aspect of the animal