XV THE AFRICAN GROUND-PIG 489 
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.” —Alhed genera, also 
South American, and without spines in their fur, are J/esomys, 
Cercomys, and Carterodon. 
The South American Zhrinacodus is also known by one 
species, 7. 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 Octo- 
dontidae is formed by the genera Myocastor, Capromys, Plagio- 
dontia, 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 7. swindernianus, the Ground-Rat of West and 
South Africa. Its structure has been investigated by Garrod, 
by Tullberg? and by myself4 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 bath 
jaws. The incisors of the upper jaw are twice grooved. There 
are thirteen dorsal vertebrae. The length of the small intestine 
is 604 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 
1 Giinther, Proc. Zool. Soc. 1879, p. 144. 2 Proc. Zool. Soc. 1873, p. 786. 
3 Loc. cit. (on p. 458), p. 128: * Proc. Zool. Soc. 1892, p. 520. 
