156 MOLLUSCA. 
type of the genus; whereas the term Amphzbulina, is founded 
on a mistake, and is apt to mislead. The Helix succinea, 
(the type of the genus), although found in damp places, is 
not amphibious. It never enters the water voluntarily. In- 
deed Miiller says, “ Sponte in aquam descendere numquam 
vidi, e contra quoties eum aque immisi, confestim egredie- 
batur.” The same remark is made by Montagu, and we 
have often witnessed its truth. 
OrpvER II.—AQUATIC. 
The aquatic pulmoniferous Gasteropoda have their resi- 
dence constantly in the water. They possess two tentacula 
only. These are usually flattened, incapable of being with- 
drawn, and having the eyes at the internal base. The food 
consists of aquatic plants. Respiration can only take place 
at the surface of the water, to which the animals occasion- 
ally ascend, to expel from the pulmonary cavity the vitiated 
air, and replenish it with a fresh supply. The sexes are 
united. The spawn, which is in the form of a rounded ge- 
latinous mass, containing many ova, 1s deposited on aquatic 
plants under water. Previous to hatching, the feetus must 
be aérated by means of some branchial arrangement. 
Genus Limnra.—Aperture of the shell having the right 
lip joined to the left at the base, and folding back on the 
pillar. 
The tentacula are lanceolated and depressed. The mouth 
is furnished with three jaws; the lateral ones simple ; the 
upper one crescent-shaped, and emarginate. The male and 
female organs, though intimately connected internally, have 
their external orifices separated to a considerable distance, 
the former issuing under the right tentaculum, the latter at 
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