MAMMALS THA T GNA W. 113 



American genus is Carterodon, which includes small rat-like animals differing- 

 from all the other members of the family inhabiting the same country in its 

 broad and grooved upper incisors ; the upper molars having one inner and 

 two outer enamel-folds, and the lower ones the reverse of this arrangement. 

 Lastly, the South American Cercomys differs from the foregoing by its 

 pointed muzzle and smooth incisors. 



The number of long, sharp spines with which the skin of .** the fretful 

 porcupine" and its allies are protected sufficiently distinguish the Hystricidce 

 from all other Rodents. These animals are of stout build 

 with the fore and hind-limbs of nearly equal length, the Porcupine Tribe, 

 front portion of the skull very short and broad, and the Family 

 molars, which may be either completely or partially rooted, Hystricidce. 

 with folds of enamel on both sides. The family may be 

 divided into two groups, one of which is confined to the New World, and the 

 other to the Old. In the American porcupines the molars are fully rooted, 

 the collar-bones complete, the upper-lip undivided, the soles of the hind- 

 f jet covered with rough tubercles, the first digit of the fore-foot wanting, 

 and numerous long hairs mixed with the spines; while the females have only 

 four teats. The numerous species of tree-porcupine (Synetheres) are con- 

 fined to the forest districts of tropical America, and are specially characterised 

 by their long, prehensile tails, short, many-coloured spines, light build, and 

 the presence of only four toes to the hind-feet ; these toes grasping against 

 a fleshy pad on the inner side of the foot. In habits these porcupines are 

 thoroughly arboreal, and also less nocturnal than their Old World allies. A 

 Brazilian species (Chwtomys) is generically distinguished on account of the 

 different conformation of its skull and more complex pattern of its molar 

 teeth. The Canadian porcupine (Erethizon) forms a kind of connecting link 

 between the New and Old World members of the family, the build being 

 heavy, and the tail stumpy and non-prehensile. The spines are almost 

 buried in the long hairs, and there are four toes in front and five behind. 



In the three Old World genera of the family, the molars are only partially 

 rooted, the collar-bones incomplete, and the soles of the hind-feet smooth, 

 while there is a rudimental first toe to the fore-foot, and the female has six 

 teats. In no case is the tail prehensile. The true porcupines (Hystrix\ 

 which are spread over the w r armer parts of Europe and Asia, as well as Africa, 

 are best characterised by their large size, highly inflated and convex skull, 

 and the short tail, terminating in a number of hollow quills, which produce a 

 rattling noise when the creatures move. These porcupines are burrowing 

 and nocturnal in their habits. The brush-tailed porcupines (Atherura), of 

 which one species is Malayan and the other two West African, differ by their 

 inferior size and long tails, the latter surmounted with a tuft of flattened 

 spines. A third genus (Trichys) is represented by a single Bornean species, 

 differing from the last in the structure of the skull ; the spines being also 

 shorter, and the bristles on the tail narrower and parallel-sided. 



This and the following families of the group are exclusively confined to 

 South and Central America and the West Indies. In the present family the 

 hind-limbs are elongated, the tail is bushy, the fur extremely 

 short, the collar-bones complete, the bony palate of the skull Cb.incb.illa Tribe, 

 narrowed in front and deeply excavated behind, the incisors Family- 

 short, and the molars separated into isolated transverse Lagostomatidce. 

 laminae by continuous folds of enamel. This family is 

 typically represented by the beautiful little chinchillas (Eriomys) of the 

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