The Cercolabidæ, or arboreal porcupines, are a group of rodents entirely confined to America, where they range from the northern limit of trees on the Mackenzie River, to the southern limit of forests in Paraguay. There is however an intervening district, the Southern United States, from which they are absent. _Erethizon_ (3 sp.), the Canadian porcupine, is found throughout {240}Canada and as far south as Northern Pennsylvania, and west to the Mississippi (Plate XX., vol. ii. p. 135); an allied species inhabiting the west coast from California to Alaska, and inland to the head of the Missouri River; while a third is found in the north-western part of South America; _Cercolabes_ (12 sp.), ranges from Mexico and Guatemala to Paraguay, on the eastern side of the Andes; _Chætomys_ (1 sp.), North Brazil. _Extinct Cercolabidæ._--A large species of _Cercolabes_ has been found in the Brazilian caves, but none have been discovered in North America or Europe. We may conclude therefore that this is probably a South American type, which has thence spread into North America at a comparatively recent epoch. The peculiar distribution of _Cercolabes_ may be explained by supposing it to have migrated northwards along the west coast by means of the wooded slopes of the Rocky Mountains. It could then only reach the Eastern States by way of the forest region of the great lakes, and then move southward. This it may be now doing, but it has not yet reached the Southern States of Eastern North America. _Family_ 67.--HYSTRICIDÆ. (3 Genera, 12 Species.) GENERAL DISTRIBUTION. __________________________________/\__________________________________ / \ NEOTROPICAL| NEARCTIC |PALÆARCTIC | ETHIOPIAN | ORIENTAL | AUSTRALIAN SUB-REGIONS|SUB-REGIONS|SUB-REGIONS|SUB-REGIONS|SUB-REGIONS|SUB-REGIONS. -----------+-----------+-----------+-----------+-----------+------------ | | | | | -- -- -- --|-- -- -- --|-- 2 -- -- |1. 2. 3 -- |1. 2. 3. 4 |-- -- -- -- | | | | | The true Porcupines have a very compact and well-marked distribution, over the whole of the Oriental and Ethiopian regions (except Madagascar), and the second Palæarctic sub-region. There is some confusion as to their sub-division into genera, but the following are those most usually admitted:--_Hystrix_ (5 sp.), South Europe to the Cape of Good Hope, all India, Ceylon, and South China; _Atherura_ (5 sp.), "brush-tailed porcupines," inhabit West Africa, India, to Siam, Sumatra, and Borneo; _Acanthion_ (2 sp.), Nepal and Malacca, to Sumatra, Borneo, and Java. _Extinct Hystricidæ._--Several extinct species of _Hystrix_ have {241}been found in the Pliocene and Miocene deposits of Europe, and one in the Pliocene of Nebraska in North America. FAMILY 68.--CAVIIDÆ. (6 Genera, 28 Species.)