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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 Eiver; 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; Chcetomys (1 sp.), North Brazil.
Extitict Cercolabidoe.—A large species of Cercolabes has been found in the Brazilian caves, Tnit 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 Bocky 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.—HYSTRICID^E. (3 Genera, 12 Species.)
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 Palsearctic sub-region. There is some confusion as to their sub-division into genera, but the following are those most usually admitted :—Hy&trix (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 HystncidcR.—Several extinct species of Hystrix have been found in the Pliocene and Miocene deposits of Europe, and one in the Pliocene of Nebraska in North America.
The Cavies and Agoutis were placed in distinct families by Mr. Waterhouse, in which he is foDowed 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; Ccelogenys (2 sp.), the paca, is found from Guatemala to Paraguay, and a second species (somewhat doubtful) in Eastern Peru; Hydrochcerus (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 Yea 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.
Extinct Caviidce.—Hydrochcerus, Ccelogenys, Dasyprocta, and Kerodon, have occurred abundantly in the caves of Brazil, and the last-named genus in the Pliocene of La Plata. Hydrochcerus 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
The Lagomyidse, 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 Eocky Mountains from about 42° to 60' north latitude.
Extinct Layomyidm.—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.
Family 70.—LEPOEID^. (1 Genus, 35-40 Species.)
Neotropical Nearctic Pal«arctic Ethiopian Oriental Australian Sub-reqionb. Sub-regions. Sub-regions. Sub-reqions. Sub-regions Sub-regions.
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.
Extinct Leporidce.—Species of Zepus 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 Muridse 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 Ethiopian, 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 Palsearctic 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 uniformity of climate, would naturally lead to less development of such a group aa this, than in the vastly more extensive and varied and almost equally luxuriant Palsearctic region of Eocene and Miocene times; while on the other hand the greater number of the smaller Carnivora in the tropics during the Pliocene and Post-Pliocene epochs, would be a constant check upon the increase of these defenceless animals, and no doubt exterminate a number of them.
The Rodents thus offer a striking contrast to the Ungulates; and these two great orders afford an admirable illustration of the different way in which physical and organic changes may affect large and small herbivorous Mammalia; often leading to the extinction of the former, while favouring the comparative development of tbe latter.
Order XL—EDENTATA. Family 71.—BEAD YPOD ID.E. (3 Genera, 12 Species.)
Neotropical I Nearctic | Palaarctic I Ethiopian I Oriental I Australian Sub-regions. [ Sub-regions. | Nitb-reoions. I 8ub-reoionb. Sub-regions. I Bur-regions.
The Sloths are a remarkable group of arboreal mammals, strictly confined to the great forests of the Neotropical region, from Guatemala to Brazil and Eastern Bolivia. None are found west of the Andes, nor do they appear to extend into Paraguay, or beyond the Tropic of Capricorn on the east coast. The genera as defined by Dr. Gray in 1871 are :—Cholcepus (2 sp.), "Sloths with two toes on fore limbs, sexes alike," Costa Rica to Brazil; Bradypus (2 sp.), " Sloths with three toes on fore limbs, sexes alike," Central Brazil, Amazon to Rio de Janeiro; Arctopitkecus (8 sp.), " Sloths with three toes on fore limbs, males with a coloured patch on the back," Costa Rica to Brazil and Eastern Bolivia (Plate XIV., voL ii. p. 24).