VERTEBRATA: MAMMALIA. 755 



Fam. 3. Caviidcz. In this family the tail is rudimentary; 

 the incisors are short ; the back teeth are rootless ; the clavicles 

 are rudimentary or wanting ; the feet are, typically, three-toed, 

 and the claws are in the form of hoof-like nails. They are all 

 South American. The Capybara (Hydrochozrus capybard) is 

 the largest of living Rodents, attaining a length of three or 

 four feet. It leads a semi-aquatic life, and has the feet incom- 

 pletely webbed. The Cavia aperea has short legs and ears, and 

 is believed to be the parent stock of the domesticated Guinea- 

 pigs; while other species of Cavy are also found in South 

 America. 



The Agoutis and Pacas are sometimes separated as a distinct 

 family (Dasyproctidcz), having long incisors, molars at first root- 

 less, but afterwards rooted, rudimentary clavicles, and five- toed 

 fore-feet. The Agouti (Dasyprocta Aguti) is found in Guiana, 

 Brazil, and Peru. Its fore-feet are five-toed, but the hind-feet 

 have only three toes. The Paca ( Ccelogenys paca) has five toes 

 on both the hind and fore feet. It has the zygomatic arches 

 enormously inflated, the maxillary portions being hollowed 

 out into chambers which are lined by mucous membrane, and 

 open into the mouth, and the use of which is quite unknown. 

 It inhabits Central and South America. 



Fam. 4. Hystricidce. In this family are the well-known Por- 

 cupines, distinguished from the other Rodents by the fact that 

 the body is covered with long spines or " quills," mixed with 

 bristly hairs. They have four back teeth on each side of each 

 jaw, and they possess imperfect clavicles. 



The true Porcupines (Hystrix) have n on -prehensile tails, 

 which are mostly furnished with long hollow spines, but some- 

 times with scales and bristles. As at present restricted, they 

 are found in the Old World only. They are mostly inhabi- 

 tants of hot climates, with the exception of the common Por- 

 cupine (ff. cristata), which occurs in Southern Europe and in 

 the north of Africa. In the genus Atherura of Asia and the 

 Indian Archipelago, the tail is long and scaly, and is termi- 

 nated by a bundle of flattened horny strips. 



Fam. 5. Cercolabidce. This family is hardly separable from 

 the preceding, the chief difference being that the animals com- 

 posing it spend more or less of their lives in trees, and are 

 therefore adapted for climbing. The Cercolabidtz comprise 

 the American Porcupines, of which the principal genera are 

 Erethizon and Cercolabes. In the genus Erethizon, represented 

 by the Canada Porcupine (E. dorsatum) of North America, the 

 quills are short, and are half hidden in the hair, and, though 

 the animal is arboreal in habit, the tail is non-prehensile. 



