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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 Mniotiltidæ, 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 Junco (genera of finches), which range over the whole United States, but 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 “Encyclopædia 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 Neo• tropical or Palæarctic 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.

1. Oreoscoptes 2. Harporhynchus 3. Sialia 4. Chamoa 5. Catherpes 6. Salpinctus 7. Psaltriparus 8. Auriparus 9. Gymnokitta 10. Picicorvus 11. Mniotilta. 12. Oporornis 13. Icteria 14. Helmintherus 15. Helminthophaga 16. Myiodioctes

17. Phænopepla
18. Xanthocephalus
19. Scolecophagus
20. Pipilo
21. Junco
22. Melospiza
23. Spizella
24. Passerculus
25. Povcetes
26. Ammodromus
27. Cyanospiza
28. Pyrrhuloxia
29. Calamospiza
30. Chondestes
31. Centronyx
32. Neocorys

33. Empidias
34. Sphyrapicus
35. Hylatomus
36. Trochilus
37. Atthis
38. Ectopistes
39. Centrocercus
40. Pediocætes
41. Cupidonia

? Ortyx
42. Oreortyx
43. Lophortyx
44. Callipepla
45. Cyrtonyx
46. Meleagris
17. Micrathene

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 2. Certhia 3. Sitta 4. Parus 5. Lophophanes 6. Lanius 7. Perisoreus 8. Pica

9. Corvus
10. Ampelis
11. Loxia
12. Pinicola
13. Linota
14. Passerelia
15. Leucosticte.

16. Euspiza
17. Plectrophanes
18. Tetrao
19. Lagopus
20. Nyctala
21. Archibuteo
22. Haliæetus

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 A romochelys 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 Silurida. Thaleichthys, one of the Salmonidæ, peculiar to the Columbia river. Moxostoma, Pimephales, Hyborhynchus, Rhinichthys, in the Eastern States; Ericymba, Ecoglossum, 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 (Accipenserida).

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 in tamilarmastica

2 Cod 18 gr. o Campi.

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 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

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