MOLLUSCA. 363 
taculum. The body of the animal is attached to the shell Mollusca. 
Mollusca. envelopes the intestine, and empties the bile into its pyloric 
by means of two muscles, which adhere to the pillar near >= 
S—\-~ extremity- The auricle and ventricle appear to occupy the 
same relative position as in the Aplysia, but the structure 
of the arteries is unknown. The organs of generation have 
also so near a resemblance as to forbid a detailed descrip- 
tion. Some species are said to eject a coloured fluid, like 
the Aplysia, from the lid of the branchie. A gland is ob- 
served in the Bulla lignaria, similar to the Aplysia, in 
which it is probable the fluid is prepared. 
The species of this genus have not been sufficiently in- 
vestigated in a living state. When preserved in spirits, it 
is impossible to form a correct idea of their true appearance, 
as exhibited when alive in sea-water, since they usually exist 
as a shapeless mass. Cuvier has given delineations of such 
preserved species, but they bearno resemblance to the figures 
of Montagu, of the same species, taken from living objects. 
M. Lamark is inclined to divide the genus into two, distin- 
guishing those who have the shell concealed, by the term 
Bullea, from such as have the shell in part exposed, which 
he retains in the genus Bulla. The shells of the genus 
Bullea are thin and white, as B. aperta; those of Bulla 
stronger, more opake, and covered with an epidermis, which, 
after the death of the animal, is easily detached, as B. lig- 
naria. 
Genus Doripicm (of Mekel). Destitute ofa dorsal plate 
or shell. There is a cavity in the cloak, with a spiral turn. 
The branchiz, and accompanying organs, are placed far be- 
hind. There is here no appearance of a spinous tongue ; 
the gullet is simple, and the stomach is membranaceous. D. 
carnosum, a native of the Mediterranean, is the type of the 
genus. 
Orver IJ]. Brancui® INTERNAL. 
The aérating organs are contained in a cavity, and appear 
in the form of sessile, pectinated ridges. 
1st Subdivision. 
Heart entire, and detached from the rectum. 
This group, forming the Pectinibranchia of Cuvier, in- 
cludes nearly all the marine Gasteropoda, which have spiral 
univalve shells. It likewise contains a few species which 
inhabit the fresh water. 
The foot is usually fortified above, on its posterior extre- 
mity, with a corneous plate, which acts as a lid to the shell, 
when the animal is withdrawn into the cavity. The ante- 
rior extremity is in some of the species double. The ante- 
rior margin of the cloak forms a thick band, or arch, rising 
from the foot, behind which is the portion of the body that 
is always contained in the shell, and which is covered with 
a very thin skin. Between the margin of the cloak and foot 
is situate the head, supported on a short neck. The tenta- 
cula are two in number, bearing eyes at their base, or on 
short lateral processes, which have some claims to be con- 
sidered as tentacula. The hood is frequently emarginate, 
and sometimes fringed. The mouth is more or less in the 
form of a proboscis, in some cases armed within with spin- 
ous lips, or furnished with a long narrow spiral tongue, armed 
with spines, as in the common periwinkle. The nature of 
this kind of tongue, the spiral extremity of which is free and 
lodged in the abdomen, is not well understood. 
The entry to the gills is by a large aperture between the 
margin of the cloak and neck, at the middle, or towards the 
right side. These are contained in a cavity on the back of 
the animal, and consist of leaves arranged in one or more 
rows, which adhere to the walls of the cavity. At the en- 
trance of this cavity is the anus and oviduct. The male and 
female organs are considered not only as distinct, but as oc- 
curring on different individuals. The evidence in support 
of this opinion is in many cases complete. The penis is in 
some external, and incapable of being withdrawn, while in 
others it is retractile, and situate in a cavity in the right ten- 
the same place, and shift their position, by an arrangement 
not well understood, in proportion as the individual increases 
in size. These muscles terminate in the foot and mouth. 
The animals of this order have not been examined suffi- 
ciently in detail, to admit of their distribution into natural 
groups, distinguished by characters founded on important 
differences of organization. The form of the shell has been 
resorted to, with the view of assisting arrangement. The 
characters thus furnished would be useful and valuable, were 
they the index of any peculiar internal structure. But, un- 
fortunately, animals widely different in structure inhabit 
shells of the same form, and vice versa, so that, however 
useful the mere conchologist may find the form of the shell 
to be in his arrangements, it can only be regarded by the 
zoologist as occupying a subordinate place. Without, there- 
fore, entering into any details regarding the structure of the 
few species which have been examined anatomically, we 
shall merely point out the tribes and families which have 
been contemplated, the characters of which in a great mea- 
sure depend on the shape of the shell. 
lst Tribe. 
Shell external. 
The shelly covering exhibits all the variations of the spi~ 
ral form. The internal structure has hitherto been in a 
great measure neglected, so that the characters employed 
in the methodical distribution of the species and genera are 
derived from the shelly appendage of the cloak. The groups, 
therefore, are merely artificial, temporary combinations, to a 
very few of which only we shall make reference. 
Genus JanTHINA.—Foot with an adhering spongy body. 
In this genus, represented by the Helix janthina of Lin- 
neus, the spongy body is capable of changing its dimen- 
sions, and enabling the animal to sink or rise in the water 
at pleasure. When irritated, the animal ejects a purple fluid 
from the cellular margin of the cloak above the gills, not 
unlike the Aplysia. This species was added to the British 
Fauna by the late Miss Hutchins. 
Genus Veturiva.—Foot simple. This genus was form- 
ed by us for the reception of the Bulla velutina of Miiller, 
(Zool. Dan. tab. ci. f. 1, 2, 3, 4), the Helix levigata of Bri- 
tish writers. The foot is destitute of lid or appendage, and 
is broad before, and pointed behind. The tentacula are two 
in number, short and filiform, with eyes at their external 
base. The head is broad and short. In addition to these 
characters given by Miiller, we have been enabled to add 
the following, from a specimen, somewhat altered, which was 
found in the stomach of a cod-fish. The animal adheres to 
the shell by two linear muscles, one on each side the cloak. 
The branchial cavity is towards the left side. The tongue 
is spinous, narrow, with its free extremity spiral. Eyes 
rather behind the tentacula. Penis exserted on the right 
side of the neck, immediately behind the eye. Cloak large 
in proportion to the size of the foot. We have termed the 
genus Velutina, bestowing on the species the trivial name 
vulgaris. 
In the following groups the anterior margin of the aper- 
ture of the shell is canaliculated. This groove in the aper- 
ture of the shell is produced by the anterior margin of the 
cloak being extended over the opening into the gills, for 
the purpose of acting like a tube or syphon, in conveying 
the water to and from the branchial cavity. The species are 
considered as oviparous, with distinct sexes in separate in- 
dividuals. 
1. Shell convoluted—The shell has an oval or linear 
mouth parallel with its length. The whorls, which are small 
segments of large circles, are wrapped round the pillar, and 
the one rising a little above the other, embrace or inclose 
the preceding ones. The four following families appear to 
belong to this division. 
