XV THE AFRICAN GROUND-PIG 489 



has but a single enamel fold, whereas in Cannahateotnys these 

 teeth have several enamel folds. The tail, moreover, is but 

 slightly hairy. 



Lonchercs with eighteen species is another Neotro^^ical 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, 

 Cerc07tiys, and Carterodon. 



The South American Thririacodvs is also known by one 

 species,^ T. alhicanda, which has rather more tlian the distal half 

 of the long tail of a white colour. The fore-feet have four toes. 

 Tlie ears are broad and short. 



Sub-Fam. 3. Capromyinae. — A tliird sub-family of tlie Octo- 

 dontidae is formed by the genera Myocastor, Caprontys, J'lagio- 

 dontia, and Tltrynomys, which are all Neotropical forms with tlie 

 exception of the last, which is African. 



Thrynoinys (better known perhaps as Aidacodus) is a genus 

 of African Eodent, containing some four species. The best- 

 known of these is T. sicinderrvianns, the Ground-Eat of West and 

 South Africa. Its structure has been investigated by Garrod,^ 

 liy Tullberg,^ and by myself.* The fur is mingled with Hattish 

 bristles ; the tail is moderately long, about hulf as long as the 

 body. The fore-feet are five- toed, but tlie two toes at each end 

 of the series are quite small. The hind-feet are only four-toed, 

 the hallux lieing absent. The claws of tlie hind-feet are stronger 

 than those of the fore-feet. The ears are not long. The limbs 

 are decidedly short, hence the name of " Ch'ound-rig " 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 tlie small intestine 

 is 60|- inches, that of the large 49 ; the caecum is short, being 

 only 8 inches long. It is a remarkable fact tliat 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 Myoimtamus, applies to a large South 

 American aquatic Eodent. The general aspect of the animal 



^ Gunther, Froc. Zool. Soc. 1879, p. 144. - Proc. Zool. S'oc. 1873, p. 786. 



2 Loc. cit. (on p. 4.58), p. 123. •* Proc. Zool. ,S'oc. 1892, p. 520. 



