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the curious glass-snake, belonging to the Zonuridae; with Phrymosoma (commonly called horned toads), Callisaurus, Uta, Euphryne, Uma, and Holbrookia, genera of Iguanidae. Testudinidae, or Tortoises, show a great development of the genus Em/s; with Aromochelys and Chel/dra as peculiar genera. Amphibia.-In this class the Nearctic region is very rich, possessing representatives of nine of the families, of which two are peculiar to the region, and there are no less than fifteen peculiar genera. Siren forms the family Sirenidae; Memobranchus belongs to the Proteidae; Amphiuma is the only representative of the Amphiumidae; there are nine peculiar genera of Salamandridae. Among the tail-less batrachians (frogs and toads) we have Scaphiopus, belonging to the Alytidae; Pseudacris to the Hylidae; and Aeris to the Polypedatidae. Fresh-water Fishes—The Nearctic region possesses no less than five peculiar family types, and twenty-four peculiar genera of this class. The families are Aphredoderidae, consisting of a single species found in the Eastern States; Percopsidae, founded on a species peculiar to Lake Superior; Heteropygii, containing two genera peculiar to the Eastern States; Hyodontidae and Amiidae, each consisting of a single species. The genera are as follows: Paralabrar, found in California; Huro, peculiar to Lake Huron; Pileoma, Boleosoma, Bryttus and Pomotis in the Eastern States—all belonging to the perch family. Hypodelus and Noturus, belonging to the Siluridae. Thaleichthys, one of the Salmonidae peculiar to the Columbia river. Morostoma, Pimephales, Hyborhynchus, Rhinichthys, in the Eastern States; Ericymba, Euroglossum, Leucosomus, and Carpiodes, more widely distributed; Cochlognathus, in Texas; Mylaphorodon and Orthodon, in California; Meda, in the river Gila; and Acrochilus, in the Columbia river—all belonging to the Cyprinidae. Scaphirhynchus, found only in the Mississippi and its tributaries, belongs to the sturgeon family (Accipenseridae). Summary of Nearctic Vertebrata. — The Nearctic region possesses 24 peculiar genera of mammalia, 49 of birds, 21 of reptiles, and 29 of fresh-water fishes, making 123 in all. Of these 70 are mammals and land-birds, out of a total of 242
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 Palaearctic region by its Procyonidae, or racoons, Hesperomys, or vesper mice, and Didelphys, 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 Arvicolae, or voles; its Sciuropterus, or flying squirrels; Tamias, or groundsquirrels; and Lagomys, or marmots, among mammals; its numerous Paridae, or tits, and Tetraonidae, or grouse, among birds; its Trionychidae among reptiles; its Proteidae, and Salamandridae, among Amphibia; and its Gasterosteidae, Atherinidae, Esocidae, 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 always 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 XXI.), 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. turnus 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, Melitara, Grapta, Chionabas, and a few others. Still, we must acknowledge, that if we formed our 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 remail, 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—Amblychile and Omus—are peculiar to the West Coast and the Rocky Mountains. Of Carabidae it possesses Dicaelus, Pasimachus, Euryfriehus, Sphaeroderus, Pinacodera, and a number of smaller genera, altogether peculiar to it; Helluomorpha, Galerita, Callida, and Tetragonoderus, 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 Buprestidae 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. Prionus is the chief representative of the Prionidae; Leptura and Crossidius of the Cerambycidae; Leptostylus, Liopus, Graphidurus, and Tetraopes, of the Lamiidae, 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.); Limaa (5 sp.); Arion (3 sp.); Ariolimax (3 sp.); Prophysaon (1 sp.); Binneia (1 sp.); Hemiphillia (1 sp.); Patula (16 sp.); Helic (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.); Pallisera (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; Ariolinae, 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 Bitlini, 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-region 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