Buprestidæ, or metallic beetles, are rather abundant in the warmer parts of the region, 27 genera being represented, nine of which are peculiar. By far the larger portion of these are confined to the Mediterranean sub-region. A considerable number also inhabit Japan and China.
The Longicorns, or long-horned beetles, are represented by no less than 196 genera, 51 of which are peculiar. They are much more abundant in the southern than the northern half of the region. Several Oriental genera extend to Japan and North China, and a few Ethiopian genera to North Africa. Thirteen genera are confined, to the two north temperate regions. Several large genera, such as Dorcadion (154 species), Phytæcia (85 species), Pogonochærus (22 species), Agapanthia (22 species), and Vesperus (7 species), are altogether peculiar to the Palæarctic region; and with a preponderance of Leptura, Grammoptera, Stenocorus, and several others, strongly characterise it as distinct from the Nearctic and Oriental regions.
The other families which are well developed in the Palæarctic regions, are, the Staphylinidæ or rove-beetles, Silphidæ or burying-beetles, Histeridæ or mimic-beetles, Nitidulidæ, Aphodiidæ, Copridæ (especially in South Europe), Geotrupidæ or dung-beetles, Melolonthidæ or chafers, Elateridæ or click-beetles, the various families of Malacoderms and Heteromera, especially Pimeliidæ in the Mediterranean sub-region, Curculionidæ or weevils, the Phytophaga or leaf-eaters, and Cocinellidæ or lady-birds.
The number of species of Coleoptera in the western part of the Palæarctic region is about 15,000, and there are probably not more than 2,000 to add to this number from Siberia, Japan, and North China; but were these countries as well explored as Europe, we may expect that they would add at least 5,000 to the number above given, raising the Palæarctic Coleopterous fauna to 20,000 species. As the total number of species at present known to exist in collections is estimated (and perhaps somewhat over-estimated) at 70,000 species, we may be sure that were the whole earth as thoroughly investigated as Europe, the number would be at least doubled, since we cannot suppose that Europe, with the Mediterranean basin, can contain more than one-fifth of the whole of the Coleoptera of the globe.
Of the other orders of insects we here say nothing, because in their case much more than in that of the Coleoptera and Lepidoptera, is the disproportion enormous between our knowledge of the European fauna and that of almost all the rest of the globe. They are, therefore, at present of comparatively little use for purposes of geographical distribution, even were it advisable to enter into the subject in a work which will, perhaps, be too much overburdened with details only of interest to specialists.
Land Shells.—These are very numerous in the warmer parts of the region, but comparatively scarce towards the North. South Europe alone possesses over 600 species, whereas there are only 200 in all Northern Europe and Asia. The total number of species in the whole region is probably about 1,250, of which the great majority are Helicidæ; the Operculated families being very poorly represented. Several small genera or sub-genera are peculiar to the region, as Testacella (West Europe and Canaries); Leucochroa (Mediterranean district); Acicula (Europe); Craspedopoma (Atlantic Islands); Leonia (Algeria and Spain); Pomatias (Europe and Canaries); Cecina (Mongolia). The largest genera are Helix and Clausilia, which together comprise more than half the species; Pupa, very numerous; Bulimus and Achatina in moderate numbers, and all the rest small. Helix is the only genus which contains large and handsome species; Bulimus and Achatina, so magnificent in tropical countries, being here represented by small and obscure forms only. Daudebardia is confined to Central and South Europe and New Zealand; Glandina is chiefly South American; Hyalina is only American and European; Buliminus ranges over all the world except America; and the other European genera of Helicidæ are widely distributed. Of the Operculata, Cyclotus, Cyclophorus, and Pupina extend from the Oriental region into Japan and North China; Tudoria is found in Algeria and the West Indies; Hydrocena is widely scattered, and occurs in South Europe and Japan. The genera of freshwater shells are all widely distributed.
The Palæarctic Sub-regions.
The four sub-regions which are here adopted, have been fixed upon as those which are, in the present state of our knowledge, at once the most natural and the only practicable ones. No doubt all of them could be advantageously again subdivided, in a detailed study of the geographical distribution of species. But in a general work, which aims at treating all parts of the world with equal fulness, and which therefore is confined almost wholly to the distribution of families and genera, such further subdivision would be out of place. It is even difficult, in some of the classes of animals, to find peculiar or even characteristic genera for the present sub-regions; but they all have well marked climatic and physical differences, and this leads to an assemblage of species and of groups which are sufficiently distinctive.
I. Central and Northern Europe.
This sub-region, which may perhaps be termed the "European," is zoologically and botanically the best known on the globe. It can be pretty accurately defined, as bounded on the south by the Pyrenees, the Alps, the Balkans, the Black Sea, and the Caucasus range; and by the Ural Mountains, or perhaps more correctly the valley of the Irtish and Caspian Sea, on the east; while Ireland and Iceland are its furthest outliers in the west. To the north, it merges so gradually into the Arctic zone that no demarcation is possible. The great extent to which this sub-region is interpenetrated by the sea, and the prevalence of westerly winds bringing warmth and moisture from an ocean influenced by the gulf-stream, give it a climate for the most part genial, and free from extremes of heat and cold. It is thus broadly distinguished from Siberia and Northern Asia generally, where a more extreme and rigorous climate prevails.