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genera of these groups, a proportion of about two-sevenths. This is the smallest proportion of peculiar genera we have found in any of the regions; but many of the genera are of such isolated and exceptional forms that they constitute separate families, so that we have no less than 12 families of vertebrata confined to the region. The Palaearctic region has only 3 peculiar families, and even the Oriental region only 12; so that, judged by this test, the Nearctic region is remarkably well characterized. We must also remember that, owing to the migration of many of its peculiar forms during the Glacial period, it has recently lost some of its speciality; and we should therefore give some weight to the many characteristic groups it possesses, which, though not quite peculiar to it, form important features in its fauna, and help to separate it from the other regions with which it has been thought to be closely allied. It is thus well distinguished from the Palsearctic region by its Procyonidae, or racoons, Hesperomys, or vesper mice, and Didclphys, or opossums, among Mammalia; by its Vireonidae, or greenlets, Mniotiltidae, or wood-warblers, Icteridae, or hang-nests, Tyrannidae, or tyrant shrikes, and Trochilidae, or humming-birds, among birds, families which, extending to its extreme northern limits must be held to be as truly characteristic of it as of the Neotropical region; by its Teidae, Iguanidae, and Cinosternum, among reptiles; and by its Siluridae, and Lepidosteidae, among fishes. From the Neotropical region it is still more clearly separated, by its numerous insectivora; by its bears; its Old World forms of ruminants ; its beaver; its numerous Arvicolas, or voles; its Sciuroplerus, or flying squirrels; Tamias, or groundsquirrels; and Larjomys, or marmots, among mammals; its numerous Paridae, or tits, and Tetraonidse, or grouse, among birds; its Trionychidae among reptiles; its Proteidae, and Salamandridse, among Amphibia; and its Gasterosteidae, Atherinidae, Esocida?, Umbridae, Accipenseridae, and Polydontidae, among fishes."
These characteristic features, taken in conjunction with the absolutely peculiar groups before enumerated, demonstrate that the Nearctic region cannot with propriety be combined with
any other. Though not very rich, and having many disadvantages of climate and of physical condition, it is yet sufficiently well characterized in its zoological features to rank as one of the well-marked primary divisions of the earth's surface.
There is one other consideration bearing on this question which should not be lost sight of. In establishing our regions we have depended wholly upon their now possessing a sufficient number and variety of animal forms, and a fair proportion of peculiar types; but when the validity of our conclusion on these grounds is disputed, we may supplement the evidence by an appeal to the past history of the region in question. In this case we find a remarkable support to our views. During the whole Tertiary period, North America was, zoologically, far more strongly contrasted with South America than it is now; while, during the same long series of ages, it was alwaya clearly separated from the Eastern hemisphere or the Palaearctic region by the exclusive possession of important families and numerous genera of Mammalia, as shown by our summary of its extinct fauna in Chapter VII. Not only may we claim North America as now forming one of the great zoological regions, but as having continued to be one ever since the Eocene period.
In describing the Palaearctic and Neotropical regions, many of the peculiarities of the insect-fauna of this region have been incidentally referred to; and as a tolerably full account of the distribution of the several families is given in the Fourth Part of our work (Chapter XXL), we shall treat the subject very briefly here.
Lepidoptera.—The butterflies of the Nearctic region have lately been studied with much assiduity, and we are now able to form some idea of their nature and extent. . Nearly 500 species belonging to about 100 genera have been described; showing that the region, which a few years ago was thought to be very poor in species of butterflies, is really much richer than Europe, and probably about as rich as the more extensive Palaearctic region. There is, however, very little speciality in the forms. A considerable number of Neotropical types enter the southern States; but there are hardly any peculiar genera, except one of the Lycaenidae and perhaps a few among the Hesperidae. The most conspicuous feature of the region is its fine group of Papilios, belonging to types (P. turnvs and P. troilus) which are characteristically Nearctic. It is also as rich as the Palaearctic region in some genera which we are accustomed to consider as pre-eminently European; such as Argynnis, Melitwa, Orapta, Chionabcut, and a few others. Still, we must acknowledge, that if we formed Out conclusions from the butterflies alone, we could hardly separate the Nearctic from the Palaearctic region. This identity probably dates from the Miocene period; for when our existing arctic regions supported a luxuriant vegetation, butterflies would have been plentiful; and as the cold came on, these would move southwards both in America and Europe, and, owing to the long continuance of the generic types of insects, would remain little modified till now.
Coleoptera.—Only a few indications can be given of the peculiarities of the Nearctic coleoptera. In Cicindelidae' the region possesses, besides the cosmopolite Cicindela, four other genera, two of which—AmUychik and Omus—are peculiar to the West Coast and the Rocky Mountains. Of Carabidae it possesses Diecelus, Pasimachus, Eurytrichus, Sphcerodems, Pinaeodera, and a number of smaller genera, altogether peculiar to it; Hdluomorpha, Galerita, Callida, and Telragonoderus, in common with South America; and a large number of characteristic European forms.
The Lucanidae are all of European types. The region is poor in Cetoniidae, but has representatives of the South American Euphoria, as well as of four European genera. Of Buprestidas it has the South American Actenodes; a single species of the Ethiopian and Eastern Belionota, in California; and about a dozen other genera of European and wide distribution.
Among Longicorns it possesses fifty-nine peculiar genera, representatives of five Neotropical, and thirteen Palaearctic genera; as well as many of wider distribution. Pi-ionua is the chief representative of the Prionidae; Leptura and Crossidius of the
Cerambycidæ; Leptostylus, Liopus, Graphidurus, and Tetraopes, of the Lamiidæ, the latter genus being confined to the region.
Terrestrial and Fluviatile Mollusca. The land-shells of temperate North America almost all belong to the Inoperculate or Pulmoniferous division; the Operculata being represented only by a few species of Helicina and Truncatella, chiefly in the Southern States. According to Mr. Binney's recent “ Catalogue of the Terrestrial Air-breathing Mollusks of North America,” the fauna consists of the following genera :-Glandina (6 sp.); Macrocyclis (5 sp.); Zonites (37 sp.); Vitrina (4 sp.); Limax (5 sp.); Arion (3 sp.); Ariolimax (3 sp.); Prophysaon (1 sp.); Binneia (1 sp.); Hemiphillia (1 sp.); Patula (16 sp.); Helix (80); Holospira (2 sp.); Cylindrella (2 sp.); Macroceramus (2 sp.); Bulimulus (8 sp.); Cionella (2 sp.); Stenogyra (4 sp.); Pupa (19 sp.); Strophia (1 sp.); Vertigo (6 sp.); Liguus (1 sp.); Orthalicus (2 sp.); Punctum (1 sp.); Succinea (26 sp.); Tebennophorus (1 sp.); Pallifera (1 sp.); Veronicella (2 sp.).
All the larger genera range over the whole region, but the following have a more restricted distribution ; Macrocyclis has only one species in the East, the rest being Californian or Central; Ariolimax, Prophysaon, Binneia, and Hemiphillia, are confined to the Western sub-region. Lower California has affinities with Mexico, 18 species being peculiar to it, of which two are true Bulimi, a genus unknown in other parts of the region. The Central or Rocky Mountain sub-region is chiefly characterised by six peculiar species of Patula. The Eastern sub-region is by far the richest, nine-tenths of the whole number of species being found in it. The Alleghany Mountains form the richest portion of this sub-region, possessing nearly half the total number of species, and at least 24 species found nowhere else. The southern States have also several peculiar species, but they are not so productive as the Alleghanies. The Canadian sub-regiou possesses 32 species, of which nearly half are northern forms more or less common to the whole Arctic regions, and several of this character have spread southwards all
over the United States. Species of Vitrina, Zonites, Pupa, and Succinea, are found in Greenland ; and Eastern Palsearctic species of Vitrina, Patula, and Pupa occur in Alaska. More than 30 species of shells living in the Eastern States, are found fossil in the Post-Pliocene deposits of the Ohio and Mississippi.
Fresh-water Shells.—North America surpasses every other part of the globe in the number and variety of its fresh-water mollusca, both univalve and bivalve. The numbers up to 1866 were as follows:—Melaniadae, 380 species; Paludinidte, 58 species; Cycladidse, 44 species; and Unionidae, 552 species. The last family had, however, increased to 832 species in 1874, according to Dr. Isaac Lea, who has made them his special study; but it is probable that many of these are such as would be considered varieties by most conchologists. Many of the species of Unio are very large, of varied forms, and rich internal colouring, and the group forms a prominent feature of the Nearctic fauna. By far the larger proportion of the fresh-water shells inhabit the Eastern or Alleghany sub-region ; and their great development is a powerful argument against any recent extensive submergence beneath the ocean of the lowlands of North America.
The Nearctic Sub-regions:
The sub-divisions of the Nearctic region, although pretty clearly indicated by physical features and peculiarities of climate and vegetation, are by no means so strongly marked out in their zoology as we might expect. The same genera, as a rule, extend over the whole region; while the species of the several sub-regions are in most cases different. Even the vast range of the Rocky Mountains has not been an effectual barrier against thU wide dispersal of the same forms of life; and although some important groups are limited by it, these are exceptions to the rule. Even now, we find fertile valleys and plateaus of moderate elevation, penetrating the range on either side; and both to the north and south there are passes which can be freely traversed by most animals during the summer. Previous to the glacial epoch there was probably a warm period, when every part of the range supported an abundant and varied