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 ; but on the 
other hand very few are generally distributed, only two — 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 Pal se arctic 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 Nearctie 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 
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