MOLLUSCA. 
Mollusca. cula, of unequal length, though in some cases one pair is 
= obsolete. 
The eyes are two in number, in the form of black 
points, seated at the tips of the posterior tentacula. 
In some of the genera the cloak is furnished with a shield, 
which is, in general, strengthened internally by a deposition 
of earthy matter, in the form of grains, or a shelly plate. 
The shield in several of the genera is placed anteriorly, 
or the shield is placed nearer the head than the tail. The 
group thus distinguished contains four genera, two of which 
have compound tails, or furnished with peculiar organs, 
while in the remaining genera the tails are simple. The 
mouth consists of lips, which are capable of small exten- 
sion, and above, the entrance is armed with a concave cor- 
neous jaw, with a notch in the middle. The tongue is merely 
armed with soft transverse ridges, pointed before, and ter- 
minated by a short cartilaginous cone. There is a sensible 
dilatation of the gullet, which marks the place of the sto- 
mach, at the under extremity of which is the rudiment of 
a ccecum at the pyloric opening. The intestine makes 
several folds, chiefly on the liver, before it reaches the anus. 
The salivary glands reach to the extremity of the gullet. 
The liver is divided into five lobes, which give rise to two 
ducts that open into the pylorus. 
The circulating system consists of two venze cavee, which 
give out numerous branches to the pulmonary cavity. The 
aérated blood is conveyed by several ducts to a simple mem- 
-branaceous systemic auricle. Between the auricle and ven- 
tricle there are two valves. The ventricle is more muscu- 
lar than the auricle. The arteries, which take their rise 
from a single aorta, are characterised by a peculiar opacity, 
and whiteness of colour, as if they were filled with milk. 
The organ of viscosity nearly encircles the pericardium. 
It consists of regularly pectinated plates. Its excretory ca- 
nal terminates at the pulmonary cavity. 
The organs of generation consist, in the female parts, of 
an ovarium, oviduct, and uterus; and in the male, of a tes- 
ticle, vas deferens, and penis, together with the peduncu- 
lated vesicle ; and, as common to both the sexual organs, 
there is a cavity opening externally, in which, by separate 
orifices, the uterus, penis, and vesicle, terminate. 
As it would be impracticable to give, even in the most 
condensed form, the characters of the numerous genera which 
have been instituted, from our limited space, we shall rather 
call the attention of the reader to the structure of a few of 
the more remarkable genera. 
Gents Arton——A mucous orifice at the termination of 
the cloak. 
This genus was instituted by M. le Baron D’Audebard de 
Férussac, in his Histoire Naturelle Générale et Particuli- 
ére des Mollusques Terrestres et Fluviatiles, folio, Paris, 
1819, 3e. liv. p. 53. The species of which it consists were 
formerly confounded with those which now constitute the 
restricted genus Limax. It differs, however, in possessing 
the mucous pore, in the pulmonary orifice being near the 
anterior margin of the shield, with the sexual orifice under- 
neath, and in the soft state of the calcareous matter, in the 
shield. The author now quoted, has described four species, 
and illustrated their characters by beautiful and expressive 
figures. The Limaz ater (together with its variety rufus) 
of British writers may be regarded as the type of the genus. 
The genus Precrrornorvs, distinguished by a conical 
protuberant shell at the termination of the cloak, was like- 
wise instituted by M. Férussac, and nearly resembles the 
preceding in form. Three species have been described 
and figured, which, however, differ remarkably from one 
another. 
Genus Limax—Pulmonary orifice near the posterior 
margin of the shield. This genus, as now restricted by 
M. Férussac, differs from the Arion in the absence of the 
caudal mucous pore, the position of the pulmonary cavity, 
and by the orifice of the sexual organs being placed under 
the superior right tentaculum. The calcareous matter of 
the shield is more solid, and appearsas a shelly plate. 
In the following genus the shield is placed nearer to the 
tail than in the preceding group, and is fortified internally 
with a subspiral plate. ; 
Genus ParmMAcriLa.—Posterior extremity of the shield 
containing the shell. The pulmonary cavity is placed un- 
derneath the shell of the shield. This arrangement oc- 
casions a corresponding posterior position to the heart. 
Along the back, from the shield to the head, are three 
grooves, the middle one of which is double. The’shield it- 
self adheres only at the posterior portion, the anterior part 
being free. The internal structure is similar to the slugs. 
The only marked difference, indeed, consists in two conical 
appendages of the sexual cavity, by which there is an ap- 
proach to the species of Helix. 
The Parmacella Olivieri is the best known species, and 
was first described, and its structure unfolded, by M. Cuvier. 
It was brought from Mesopotamia by M. Olivier. 
In the two following genera the cloak is destitute of a 
shield, and the pulmonary cavity is situated near the tail. 
Genus TrestTaceLLa.—tTail covered with a single spiral 
shell, underneath which is the pulmonary cavity. The vent 
and pulmonary cavity are, from the position of the protect- 
ing shell, on which they are dependent, nearly terminal. 
The foot extends on each side beyond the body. From the 
manner in which the blood is aérated, the auricle and ven- 
tricle are placed longitudinally, the latter being anterior. 
Genus Oncurprum.—Cloak tuberculated. Snout en- 
larged and emarginate. Tentacula two in number, with 
eyes at the tips. This genus was instituted by Dr. Buchan- 
an, (now Hamilton), in Zin. Trans., vol. v. p. 132, for the 
reception of a species which he found in Bengal, on the 
leaves of Typha Elephantina. It is not, according to this 
naturalist, “like many others of the worm kind, an herma- 
phrodite animal ; for the male and female organs of genera- 
tion are in distinct individuals. I have not yet perceived 
any mark to distinguish the sexes, while they are not in 
copulation; as, in both, the anusand sexual organs are placed 
in a perforation, (cloaca communis), in the under part of the 
tail, immediately behind the foot ; but, during coition, the 
distinction of sexes is very evident, the penis protruding to 
a great length, considering the size of the animal.” 
2d Subdivision. 
Cloak and foot not parallel; the viscera contained in a 
spiral, dorsal protuberance, protected by a shell. 
This group includes the animals usually denominated 
Swarts. They bear a very close resemblance to the slugs. 
The shield, however, has a thickened margin in front, des- 
tined to secrete the matter of the shell. In the part corres- 
ponding with the centre of the shield in the slugs, there is, 
(as Cuvier has characteristically termed it), a natural rup- 
ture, through which the viscera are protruded into a conical 
bag twisted spirally. In this bag are contained the principal 
viscera, the liver occupying its extremity. The body of the 
animal is attached to the pillar of the shell by a complicated 
muscle, which shifts its place with the growth of the animal. 
The mouth is furnished above with a thin-arched corneous 
mandible, notched on the edges. The whole body, includ- 
ing the foot and head, are, in general, capable of being with- 
drawn into the cavity of the shell. In two genera the aper- 
ture is closed by a lid. 
Genus Cyctostoma.—Aperture of the shell circular. 
The tentacula are linear and subretractile. The primary 
ones have subglobular, highly-polished extremities, con- 
sidered by Montagu as the eyes. The true eyes, however, 
are placed at the exterior base of the large tentacula, and 
are elevated on tubercles, which are the rudiments of the 
second pair. The aperture of the pulmonary cavity is situ- 
ated on the neck. The sexes are likewise separate; the 
penis of the male being large, flat, and muscular. The 
357 
Mollusca. 
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