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,[[343]] 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,[[344]] by Tullberg,[[345]] and by myself.[[346]] 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
suggests a Water-Rat of large size (it has been exhibited in shows as a phenomenal product of London sewers!); the tail is nearly as long as the body. The ears are small. The limbs are short. The tail is naked. The hind-feet are webbed, but not so much so as in Hydromys. A small thumb is present. The animal has thirteen pairs of ribs; the molars are four in each jaw. The large intestine is more than three times the length of the small, and the caecum is, as in the last genus, relatively short.
Capromys is a genus[[347]] which is remarkable on account of its restricted distribution. It is found only in the islands of Cuba and Jamaica. There are four species, of which C. melanurus is a dark brown-coloured animal with a blacker tail, nearly as large as a Rabbit. The native name of this Rodent is "hutia." It is also remarkable for having a stomach more complicated than is the rule among the mammals of this group. The organ is divided by two constrictions into three compartments. In C. pilorides the liver is occasionally divided up in an extraordinary fashion into small lobules. Capromys has the large number of sixteen dorsal vertebrae.
Fam. 2. Ctenodactylidae.—For these African genera it seems admissible to form a distinct family, though Thomas, and Flower and Lydekker, only allow to the genera Ctenodactylus, Pectinator, and Massoutiera sub-family rank. On the other hand, Tullberg removed these genera entirely from the Hystricomorph section and placed them as a section of the sub-tribe Myomorphi of the tribe Sciurognathi. It was chiefly the form of the mandible which led to this placing, for in these Rodents, as in all Squirrel- and Rat-like Rodents, and unlike what is found in the Hystriciform genera, the angular process of the mandible is not bent sideways.
The genus Ctenodactylus derives its name from the peculiar strong bristles which form a comb-like structure upon the hind-feet and hide the claws; these are stated to be for the purpose of dressing the fur. The Gundi of North Africa, C. gundi, has a length of 190 mm., with a short tail of 17 mm. The ears are only moderate in size. The dental formula of the molars is 4/3. The incisors are white. The feet have four digits, and the hind-limbs are the longer. The large intestine is distinctly longer than the small intestine.