358 
MOLLUSCA. 
Mollusca. mouth is formed into a kind of proboscis, and the upper lip 
“=~ is deeply emarginate. 
Genus Herrx—Snail. Aperture of the shell lunulat- 
ed; the width and length nearly equal. The snails differ 
from the slugs chiefly in the organs of reproduction. The 
vagina, previous to its termination in the sexual cavity, is 
joined by the canal of the vesicle, and by two ducts, each 
proceeding from a bundle of multifid vesicles. Each bundle 
consists of a stem or duct, and numerous branches, with blunt 
terminations. These organs secrete a thin milky fluid, the 
use of which is unknown. 
Connected with the sexual cavity is the bag in which the 
darts are produced. ‘The bag itself is muscular, with lon- 
gitudinal grooves, and a glandular body at the extremity. 
This glandular body secretes the dart, which is in the form 
of a lengthened pyramid, consisting of calcareous filaments 
nearly resembling asbestus. Previous to the sexual union, 
the two snails touch each other repeatedly with the mouth 
and tentacula, and at last the dart of the one is pushed forth 
by its muscular bag, and. directed against the body of the 
other, into which it enters, never penetrating through the 
integuments, and even, in many_cases; falling short of its 
mark. Whether the use of the dart is merely to stimulate, 
or whether it is subservientto any other purpose, canscarcely 
be said to be determined. 
The species belonging to this genus are numerous, and 
exhibit, in the form, the markings, and the coverings of the 
shell, numerous characters for their subdivision. 
The species which are related to the Turbo dcdens per- 
versus and museorum of Linneus, constitute a very natural 
family, which may be termed Purana, distinguished by the 
mouth being, in general, furnished with teeth, or testaceous 
lamin, and the last whorl nearly the same as the preceding. 
Perhaps the most convenient way of dividing them is into 
two sections, the first including the dextral and the second 
the sinistral shells. 
Genus Virriva—Margin of the shield double. The 
upper fold of the shield is divided into several lobes, which 
are capable of being reflected over the surface of the shell. 
The shell itself is not capable of containing the whole body 
of the animal. The Helix pellucida of Miiller is the type 
of the genus. It is a common British species, and was has- 
tily regarded by Montagu as the fry of the Helix lucida. 
Gents Succrsea.—Termination of the pillar rounded. 
The mouth is large in proportion to the size of the shell, 
with the outer lip thin, and the pillar attenuated. The genus 
was first characterized by Draparnaud and named Suc- 
crnEA. Afterwards Lamark proposed the term Amphibu- 
lina, but latterly adopted that of Draparnaud. Thename first 
employed indicates one of the most striking characters of the 
typeof 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. 
Orvper I]. 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, is deposited on aquatic 
plants under water. Previous to hatching, the foetus must Mollusca. 
be aérated by means of some branchial arrangement. 
Genvs Limyes.—Aperture of the shell having the right 
lip joined to the left at the base, and folding back on the 
ilar. 
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 
the pulmonary cavity. In consequence of this arrangement, 
the individuals of Z. stagnalis have been observed by Geot- 
froy and Miiller to unite together in a chain during coition, 
the first-and last members of the series exercising only one 
of the sexual functions, the intervening individuals impreg- 
nating and receiving impregnation at the same time. Whe- 
ther this is the constant or only accidental practice of this 
species, does not appear to be determined. We know that 
many other species of the genus are mutually impregnated, 
as usual, in pairs only. 
The species of this genus are numerous. They reside in 
pools, lakes, and rivers, and furnish a favourite repast to the 
different kinds of trouts,and water-fowl. 
With regard to the Limnea auricularia, it would appear, 
from the observations of Draparnaud, (Histoire des Mol- 
lusques,” p.49,) that it exhibits a very singular structure of 
the respiratory organs. We shall cuote his own words: 
“T’animal est pourvu de quatre filamens ou tubes qui par- 
tent de la partie supérieure du cou, prés du manteau; ce sont 
des trachées. Cestubes sont longs, blancs et trés transparens, 
et on ne les distingue bien qu’ 4 la loupe. Leur surface est 
comme rugueuse, et leur extrémité est un peu renflée. Ils 
sont rétractiles. L’animal les fait sortir 4 volonté, un, deux, 
trois ensemble : il les agite et les contourne sans cesse en 
divers sens: ce qui fait qu’on les prendroit pour de petits 
vers. Je présume que par ce movement ces organes sépa- 
rent de leau lair que y’est contenu et labsorbent. Cet 
animal est trés sujet, ainsi que les autres gastéropodes flu- 
viatiles, 4 étre infesté par le nats vermicularis, qui se loge 
ordinairement entre le cou et le manteau, au-dessous des 
tentacules, et s’agite sans cesse d’un movement vermicu- 
laire.” But little doubt, we think, can be entertained that 
this naturalist had been deceived by some of the parisitical 
leeches which infest the aquatic pulmonifera, and that, instead 
of breathing by means of tubular gills, the animal of the Z. 
auricularia possesses, like those which it resembles in other 
characters, a pulmonary cavity. 
Genus Puysa—Pillar-lip destitute of a fold, and the 
whorls are sinistral. (Zool. Journ. vii. 363.) The external ap- 
pearance of the animal issimilar to the Limnea; but the mar- 
gin of the cloak is loose, divided into lobes, and capable of 
being refleeted over the surface of the shell near the mouth. 
This genus was instituted by Draparnaud. The Bulla fonti- 
nalis of British authors is regarded as the type of the genus. 
Genus ApLexa.—Pillar-lip, with a fold. This genus 
was instituted by us for the reception of the Bulla hypnorum 
and rivalis of British writers. The shell is more produced 
than in the Physa. The cloak of the animal is incapable of 
being reflected on the shell, and its margin is destitute of 
lobes. 
Genus Pranorpis.—Cavity of the shell entire. Thisis 
another sinistral genus; the vent, pulmonary cavity, and 
sexual organs, being on the left, and the heart on the right 
side. The P. corneus, the type of the genus, pours forth, 
when irritated, a purple fluid from the sides, betweenthe foot 
and the margin of the cloak. 
Gents SrGMEenTINA.—Cavity of the shell divided. Ex- 
ternally, the shell appears similar to Planorbis ; but inter- 
nally, it is divided by testaceous, transverse partitions, into 
several chambers, which communicate with each other by 
