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CHAP. XXII.] MOLLUSCA. 513
to the limit of trees or even considerably beyond it, in the
Arctic regions ; but they are comparatively very scarce in all
cold countries. The Antilles, the Philippine Islands, Equa-
torial America, and the Mediterranean sub-region are especially
rich in this family. Comparatively few of the genera, and those
generally small ones, are restricted to single regions ;
other hand very few are generally distributed, only two
—
but on the
Helix
and Pupa—occurring in all the six regions, while Helix alone is
truly cosmopolitan, occurring in every sub-region, in every
country, and perhaps in every island on the globe.
The Neotropical region is, on the whole, the richest in this
family, the continental Equatorial districts producing an abun-
dance of large and handsome species, while the Antilles are
pre-eminent for the number of their peculiar forms. This
region possesses 22 of the genera, and 6 of them are peculiar.
The Palsearctic region seems to come next in productiveness,
but this may be partly owing to its having been so thoroughly
explored. It possesses 16 of the genera, and 3 of them are
confined to it. The great mass of the species are found in
the warm and fertile countries surrounding the Mediterranean
Sea.
The Ethiopian region has 13 genera, only one of which is
peculiar.
The Australian region has 14 genera, 2 of which are confined
to the Pacific Islands.
The Oriental has 15 genera and the Nearctic 12, but in
neither case are there any peculiar generic types.
The following is the distribution of the several genera taken
in the order of their magnitude :
—
Helix (1,115 sp.), cosmopolitan. This genus is divided into
88 sub-genera, a number of which have a limited distribution.
An immense quantity of species have been recently described,
so that the number now exceeds 2,000.
Nanina (290 sp.) is characteristic of the Oriental and Aus-
tralian regions, over the whole of which it extends, just entering
the Palsearctic region as far as North China and Japan.
Isolated from this area is a small group of 4 species occurring