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of Panama. The genera are as follows:–Dactylomys (2 sp.), Guiana and Brazil; Cercomys (1 sp.), Central Brazil; Lasiuromys (1 sp.), San Paulo, Brazil; Petromys (1 sp.), South Africa; Myopotamus (1 sp.), the coypu, on the East side of the Andes from Peru to 42° S. lat., on the West side from 33° to 48° S. lat. ; Carterodon (1 sp.), Minaes Geraes, Brazil; Aulacodes (1. sp.), West and South Africa; Mesomys (1 sp.), Borba on the Amazon; Echimys (11 sp.), from Guiana and the Ecuadorian Andes to Paraguay; Loncheres (10 sp.), New Granada to Brazil.

Fossil and Extinct Echimyidae.—The genus Carterodon was established on bones found in the Brazilian caves, and it was several years afterwards that specimens were obtained showing the animal to be a living species. Extinct species of Myopotamus and Loncheres have also been found in these caves, with the extinct genera Lonchophorus and Phyllomys.

No remains of this family have been discovered in North America; but in the Miocene and Upper Eocene deposits of France there are many species of an extinct genus Theridomys, which is said to be allied to this group or to the next (Cercolabidae). Aulacodon, from the Upper Miocene of Germany, is allied to the West African Aulacodes; and some other remains from the lower Miocene of Auvergne, are supposed to belong to Echimys.

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The Cercolabidae, 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 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; Chaetomys (1 sp.), North Brazil.

Eatinct Cercolabidae.—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.

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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 Palaearctic sub-region. There is some confusion as to their sub-division into genera, but the following are those most usually admitted;—Hystria (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 Hystricidae.—Several extinct species of Hystria, have been found in the Pliocene and Miocene deposits of Europe, and one in the Pliocene of Nebraska in North America.

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The Cavies and Agoutis were placed in distinct families by Mr. Waterhouse, in which he is followed by Professor Carus, but they have been united by Professor Lilljeborg, and without pretending to decide which classification is the more correct I follow the latter, because there is a striking external resemblance between the two groups, and they have an identical distribution in the Neotropical region, and with one exception are all found east of the Andes. Dasyprocta (9 sp.), the agouti, ranges from Mexico to Paraguay, one species inhabiting the small West Indian islands of St. Vincent, Lucia, and Grenada; Coelogenys (2 sp.), the paca, is found from Guatemala to Paraguay, and a second species (some. what doubtful) in Eastern Peru; Hydrochaerus (1 sp.), the capybara, inhabits the banks of rivers from Guayana to La Plata; Cavia (9 sp.), the guinea-pigs, Brazil to the Straits of Magellan, and one species west of the Andes at Yga in Peru; Kerodon (6 sp.), Brazil and Peru to Magellan; Dolichotis (1 sp.), the Patagonian cavy, from Mendoza to 48° 30' south latitude, on sterile plains.

Eatinct Caviidae.—Hydrochaerus, Caelogenys, Dasyprocta, and Kerodon, have occurred abundantly in the caves of Brazil, and the last-named genus in the Pliocene of La Plata. Hydrochorus has been found in the Post-Pliocene deposits of South Carolina. Cavia and Dasyprocta are said to have been found in the Miocene of Switzerland and France. No well-marked extinct genera of this family have been recorded.

If the determination of the above-mentioned fossil species of Cavia and Dasyprocta are correct, it would show that this now exclusively South American family is really derived from Europe, where it has long been extinct.

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The Lagomyidae, or pikas, are small alpine and desert animals which range from the south of the Ural Mountains to Cashmere and the Himalayas, at heights of 11,000 to 14,000 feet, and northward to the Polar regions and the north-eastern extremity of Siberia. They just enter the eastern extremity of Europe as far as the Volga, but with this exception, seem strictly limited to the third Palaearctic sub-region. In America they are confined to the Rocky Mountains from about 42° to 60' north latitude.

Extinct Lagomyidae.—Extinct species of Lagomys have occurred in the southern parts of Europe, from the Post-Pliocene to the Miocene formations. Titanomys, an extinct genus, is found in the Miocene of France and Germany.

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The Hares and Rabbits are especially characteristic of the Nearctic and Palaearctic, but are also thinly scattered over the Ethiopian and Oriental regions. In the Neotropical region they are very scarce, only one species being found in South America, in the mountains of Brazil and various parts of the Andes, while one or two of the North American species extend into Mexico and Guatemala. In the Nearctic region, they are most abundant in the central and western parts of the continent, and they extend to the Arctic Ocean and to Greenland. They are found in every part of the Palaearctic region, from Ireland to Japan; three species range over all India to Ceylon, and others occur in Hainan, Formosa, South China, and the mountains of Pegu ; the Ethiopian region has only four or five species, mostly in the Southern extremity and along the East coast. An Indian species is now wild in some parts of Java, but it has probably been introduced. Eactinct Leporidae.—Species of Lepus occur in the Post-Pliocene and Newer Pliocene of France; but only in the PostPliocene of North America, and the caves of Brazil.

General Remarks on the Distribution of the Rodentia.

With the exception of the Australian region and Madagascar, where Muridae alone have been found, this order is one of the most universally and evenly distributed over the entire globe. Of the sixteen families which compose it, the Palaearctic region has 10; the Fthiopian, Nearctic, and Neotropical, each 9; and the Oriental only 5. These figures are very curious and suggestive. We know that the rodentia are exceedingly ancient, since some of the living genera date back to the Eocene period; and some ancestral types might thus have reached the remote South American and South African lands at the time of one of their earliest unions with the northern continents. In both these countries the rodents diverged into many special forms, and being small animals easily able to conceal themselves, have largely survived the introduction of higher Mammalia. In the Palaearctic and Nearctic regions, their small size and faculty of hibernation may have enabled them to maintain themselves during those great physical changes which resulted in the extermination or banishment of so many of the larger and more highly organised Mammalia, to which, in these regions, they now bear a somewhat inordinate proportion. The reasons why they are now less numerous and varied in the Oriental region, may be of two kinds. The comparatively small area of that region and its

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