SYSTEMATIC 
OES NG gale bas) oY, 
Susctiss PULMONATA. 
This division embraces all the land and fresh-water mollusca 
which breathe air. They are normal gastropods, having a broad 
foot, and usually a large spiral, holostomate, inoperculate shell 
(operculate in Amphibola). Their breathing organ is the sim- 
plest form of lung, resembling the branchial chamber of the sea- 
snails, but lined with a network of respiratory vessels. The 
respiratory orifice is small and contractile to prevent too rapid 
desiccation in the land-snails, and to exclude water in the aquatic 
genera. Most of them have sufliciently large shells to contain 
the animal; in a few the shell only shelters a portion of the 
animal, or it is internal and of simple structure, or rarely absent. 
Snail-shells contain a larger proportion of animal matter than 
sea-shells, and their structure is less distinctly stratified. The 
Pulmonata are mostly terrestrial, but some genera are fluviatile 
and a few inhabit damp places near the sea, where at high-tide 
they are covered by its waters. The sexes are united in each 
individual, but the genital orifices are sometimes contiguous, 
opening ina common cloaca, and sometimes distant. Through 
the Cyclostomez or operculated land-snails and the Ampullarize 
they are related to the phytophagous sea-snails, through Siphon- 
aria and Gadinia to the limpets, and through Onchidium to the 
nudibranchs. 
Land-snails are universally distributed ; but the necessity for 
moist air,and the vegetable nature of their food, favor their 
multiplication in warm and humid regions: they are especially 
abundant in islands, whilst in hot and desert countries they 
appear only in the season of rain or dews. ‘Their geological 
history is less complete than that of the purely marine orders ; 
but their antiquity might be inferred from the distribution of 
peculiar genera in remote islands, associated with the living rep- 
resentatives of the ancient fauna of Europe. Fresh-water snails 
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