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remarkable and characteristic skunks is separated by Dr. J. E. Gray as a genus—Spilogale. In the American family Procyonidse, a peculiar genus (Bassaris) is found in California and Texas, extending south along the mountains of Mexico and Guatemala. Eumetopias, and Halicyon, are seals confined to the west coast of North America. The Bovidse, or hollow-horned ruminants, contain three peculiar forms; Antilocapra, the remarkable prong-buck of the Rocky Mountains ; Aplocerus, a goatlike antelope; and Ovibos, the musk-sheep, confined to Arctic America and Greenland. Among the Rodents are many peculiar genera: Neotoma, Sigmodon, and Fiber, belong to the Muridse, or rats; Jaculus to the Dipodidae, or jerboas. The very distinct family Saccomyidcc, or pouched rats, which have peculiar cheek pouches, or a kind of outer hairy mouth, consists of five genera all confined to this region, with one of doubtful affinities in Trinidad and Central America. In the squirrel family (Sciuridae), Cynomys, the prairie-dogs, are peculiar; and Tamias, the ground squirrel, is very characteristic, though found also in North Asia, Haploodon, or sewellels, consisting of two species, forms a distinct family; and ErctMzon is a peculiar form of tree porcupine (Cercolabidas). True mice and rats of the genus Mus are not indigenous to North America, their place being supplied by a distinct genus (Hesperomys), confined to the American continent.
Birds.—The genera of birds absolutely peculiar to the Nearctic region are not very numerous, because, there being no boundary but one of climate between it and the Neotropical region, most of its characteristic forms enter a short distance within the limits we are obliged to concede to the latter. Owing also to the severe winter-climate of a large part of the region (which we know is a comparatively recent phenomenon), a large proportion of its birds migrate southwards, to pass the winter in the West-Indian islands or Mexico, some going as far as Guatemala, and a few even to Venezuela.
In our chapter on extinct animals, we have shown, that there is good reason for believing that the existing union of North and South America is a quite recent occurrence; and that the separation was effected by an arm of the sea across what is now Nicaragua, with perhaps another at Panama. This would leave Mexico and Guatemala joined to North America, and forming part of the Nearctic region/although no doubt containing many Neotropical forms, which they had received during earlier continental periods; and these countries might at other times have been made insular by a strait at the isthmus of Tehuantepec, and have then developed some peculiar species. The latest climatal changes have tended to restrict these Neotropical forms to those parts where the climate is really tropical; and thus Mexico has attained its present strongly marked Neotropical character, although deficient in many of the most important groups of that region
In view of these recent changes, it seems proper not to draw any decided line between the Nearctic and Neotropical regions, but rather to apply, in the case of each genus, a test which will show whether it was probably derived at a comparatively recent date from one region or the other. The test referred to, is the existence of peculiar species of the genus, in what are undoubtedly portions of ancient North or South America. If, for example, all the species of a genus occur in North America, some, or even all, of, them, migrating into the Neotropical region in winter, while there are no peculiar Neotropical species, then we must class that genus as strictly Nearctic; for if it were Neotropical it would certainly have developed some peculiar resident forms. Again, even if there should be one or two« resident species peculiar to that part of Central America north of the ancient dividing strait, with an equal or greater number of species ranging over a large part of Temperate North America, the genus must still be considered Nearctic. Examples of the former case, are Helminthophaga and Myiodioctes, belonging to the Mniotiltida?, or wood-warblers, which range over all Temperate North America to Canada, where all the species are found, but in each case one of the species is found in South America, probably as a winter "migrant. Of the latter, are Ammodramus and Junto (genera of finches), which range over the whole United States, bnt each have one peculiar species in Guatemala. These
may be claimed as exclusively Nearctic genera, on the ground that Guatemala was recently Nearctic; and is now really a transition territory, of which the lowlands have been invaded and taken exclusive possession of by a Neotropical fauna, while the highlands are still (in part at least) occupied by Nearctic forms. In his article on "Birds," in the new edition of the "Encyclopaedia Britannica" (now publishing), Professor Newton points out, that the number of peculiar genera of Nearctic birds is much less than in each of the various sub-divisions of the Neotropical region; and that the total number of genera is also less, while the bulk of them are common either to the Neotropical or Palaearctic regions. This is undoubtedly the case if any fixed geographical boundary is taken; and it would thus seem that the "Nearctic" should, in birds, form a sub-region only. But, if we define "Nearctic genera" as above indicated, we find a considerable amount of speciality, as the following list will show. The names not italicised are those which are represented in Mexico or Guatemala by peculiar species:—
List Of Typical Nearctic Genera Of Land Birds.
The above are all groups which are either wholly Nearctic or typically so, but entering more or less into the debatable ground of the Neotropical region; though none'possess any peculiar species in the ancient Neotropical land south of Nicaragua. But we have, besides these, a number of genera which we are accustomed to consider as typically European, or Palaearctic, 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 which have as much right to be considered typically Nearctic as Palaearctic:—
1. Regulus 9. Corvus 16. Euspiza
2. Certhia 10. Ampelis 17. PUeirophana
3. Sitta 11. Loxia 18. Tetrao
4. Parus 12. Pinicola 19. Lagopus
5. Lophophanes 13. Linota 20. Nyctala
6. Lanius 14. Passerdla 21. Archibutei
7. Pemoreus 15. Leucosticte. 22. Haliseetus
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 Palaearctic 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 Palaearctic.
Jleptiles.—-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, Pittiophis, and Ischnognathus, belonging to the Colubridae; Farancia, and Dimodes, Homalopsidae; Lichanotus, one of the Pythonidae; Cenchris, Crotalophorus, Uropsophorus, and Crotaius, belonging to the Crotalidae or rattlesnakes.
Of Lizards, Chirotes, forming a peculiar family; Ophisaurus,
the curious glass-snake, belonging to the Zonuridss; with Phrynosoma (commonly called homed toads), Callisaurus, Uta, Euphryne, Uma, and Holbroohia, genera of Iguanidae.
Testudinidae, 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 Sirenidae; Menobranchtis belongs to the Proteidae; Amphiuma is the only representative of the Amphiumidse; there are nine peculiar genera of Salamandridae. Among the tail-less batrachians (frogs and toads) we have Scaphiopus, belonging to the Alytidse; Pseudacris to the Hylidae; and Acris 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 Aphredoderidse, 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: 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 Siluridas. Thaleichthys, one of the Salmonidae peculiar to the Columbia river. Moxostoma, Pimephales, Hyhorhynchus, Rhinichthys, in the Eastern States; Ericymba, Exoglossum, Leucosomus, and Garpiodes, more widely distributed; Cuchlognathus, 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