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 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 which have as much right to be considered typically Nearctic as Palæarctic:—
| 1. Regulus | 9. Corvus | 16. Euspiza |
| 2. Certhia | 10. Ampelis | 17. Plectrophanes |
| 3. Sitta | 11. Loxia | 18. Tetrao |
| 4. Parus | 12. Pinicola | 19. Lagopus |
| 5. Lophophanes | 13. Linota | 20. Nyctala |
| 6. Lanius | 14. Passerelia | 21. Archibuteo |
| 7. Perisoreus | 15. Leucosticte | 22. Haliæetus |
| 8. Pica |
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, 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 Arvicolæ, or voles; its Sciuropterus, or flying squirrels; Tamias, or ground-squirrels; 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.