« EelmineJätka »
tomed to consider as typically European, or Palæarctic, having representatives in North America ; although in many cases it would be more correct to say that they are Nearctic genera, represented in Europe, since America possesses more species than Europe or North Asia. The following is a list of genera whieh have as much right to be considered typically Nearctic as Palæarctic:
The seven genera italicized have a decided preponderance of Nearctic species, and have every right to be considered typically Nearctic ; while the remainder are so well represented by peculiar species, that it is quite possible many of them may have originated here, rather than in the Palæarctic region, all alike being quite foreign to the Neotropical.
On the whole, then, we have 47 in the first and 7 in the second table, making 54 genera which we may fairly class as typically Nearctic, out of a total of 168 genera of land- birds, or nearly one-third of the whole. This is an amount of peculiarity which is.comparable with that of either of the less isolated regions ; and, combined with the more marked and more exclusively peculiar forms in the other orders of vertebrates, fully establishes Temperate North America as a region, distinct alike from the Neotropical and the Palæarctic.
Reptiles.-Although temperate climates are always comparatively poor in reptiles, a considerable number of genera are peculiar to the Nearctic region. Of snakes, there are, Conophis, Chilomeniscus, Pituophis, and Ischnognathus, belonging to the Colubridæ; Farancia, and Dimodes, Homalopsidæ; Lichanotus, one of the Pythonidæ; Cenchris, Crotalophorus, Uropsophorus, and Crotalus, belonging to the Crotalidæ or rattlesnakes.
Of Lizards, Chirotes, forming a peculiar family ; Ophisaurus, VOL. II.-9
the curious glass-snake, belonging to the Zonuridæ; with Phrynosoma (commonly called horned toads), Callisaurus, Uta, Euphryne, Uma, and Holbrookia, genera of Iguanidæ.
Testudinidæ, or Tortoises, show a great development of the genus Emys; with Aromochelys and Chelydra 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 Sirenidæ ; Menobranchus belongs to the Proteidæ; Amphiuma is the only representative of the Amphiumidæ; there are nine peculiar genera of Salamandridæ. Among the tail-less batrachians (frogs and toads) we have Scaphiopus, belonging to the Alytidæ ; Pseudacris to the Hylidæ; and Acris to the Polypedatidæ.
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 Aphredoderidæ, consisting of a single species found in the Eastern States; Percopsidæ, founded on a species peculiar to Lake Superior; Heteropygii, containing two genera peculiar to the Eastern States; Hyodontidæ and Amiidæ, each consisting of a single species. The genera are as follows: Paralabrax, 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 Siluridæ. Thaleichthys, one of the Salmonidæ peculiar to the Columbia river. Moxostoma, Pimephales, Hyborhynchus, Rhinichthys, in the Eastern States; Ericymba, Exoglossum, 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 Cyprinidæ. Scaphirhynchus, found only in the Mississippi and its tributaries, belongs to the sturgeon family (Accipenseridæ).
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 Palæarctic 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 Palæarctic region by its Procyonidæ, or racoons, Hesperomys, or vesper mice, and Didelphys, or opossums, among Mammalia ; by its Vireonidæ, or greenlets, Mniotiltidæ, or wood-warblers, Icteridæ, or hang-nests, Tyrannidæ, or tyrant shrikes, and Trochilidæ, 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 Teidæ, Iguanidæ, and Cinosternum, among reptiles; and by its Siluridæ, and Lepidosteidæ, 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 Arvicolo, or voles; its Sciuropterus, or flying squirrels; Tamias, or groundsquirrels; and Lagomys, or marmots, among mammals; its numerous Paridæ, or tits, and Tetraonidæ, or grouse, among birds; its Trionychidæ among reptiles ; its Proteidæ, and Salamandridæ, among Amphibia ; and its Gasterosteidæ, Atherinidæ, Esocidæ, Umbridæ, Accipenseridæ, and Polydontidæ, 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 Palæarctic 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.
Insects. In describing the Palæarctic 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 Palæarctic 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 Lycænidæ and perhaps a few among the Hesperidæ. 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 Palæarctic region in some genera which we are accustomed to consider as pre-eminently European; such as Argynnis, Melitæa, 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 Palæarctic 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 Cicindelidæ 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 Carabidæ it possesses Dicælus, Pasimachus, Eurytrichus, Sphæroderus, 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 Lucanidæ are all of European types. The region is poor in Cetoniidæ, but has representatives of the South American Euphoria, as well as of four European genera. Of Buprestidæ it has the South American Actenodes ; a single species of the Ethiopian and Eastern Belionoto, 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 Palæarctic genera; as well as many of wider distribution. Prionus is the chief representative of the Prionidæ; Leptura and Crossidius of the