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MOLLUSCOUS ANIMALS,

INCLUDING

SHELL FISH;

CONTAINING AN

EXPOSITION OF THEIR STRUCTURE, SYSTEMATICAL

ARRANGEMENT, PHYSICAL DISTRIBUTION,

AND DIETETICAL USES,

WITH A REFERENCE TO THE EXTINCT RACES.
FORMING THE ARTICLE " MOLLUSCA" IN THE SEVENTH EDITION OF THE

ENCYCLOPEDIA BRITANNICA.

BY

JOHN FLEMING, D.D. F.R.S.E. M.W.S. &c.

PROFESSOR OF NATURAL PHILOSOPHY IN THE UNIVERSITY AND KING'

COLLEGE, ABERDEEN,

AUTHOR OF " THE PHILOSOPHY OF ZOOLOGY," " HISTORY
OF BRITISH ANIMALS," &c.

EDINBURGH :
ADAM AND CHARLES BLACK, NORTH BRIDGE,

BOOKSELLERS TO HER MAJESTY.

MDCCCXXXVII.

PALEO,
LIBR,

Gift of C. A. Kofoid

EDINBURGH :
BALFOUR St JACK, Printers, Niddry Street.

'A
D

CONTENTS.

Pago.

DISTINGUISHING CHARACTERS OF MOLLUSCOUS ANIMALS, 1

CHAPTER I.

PHYSIOLOGY.

1. Structure and appendages of the skin. The formation of

shells, 3

2. Muscular system. Modes of rest and motion, 10

3. Nervous system. The brain. Organs of sense, 12

4. Digestive system. Phytivorous and carnivorous Mollusca.

Tentacula. Salivary glands. Stomach and biliary organs, 14

5. Circulating system. Lungs. Gills, -§ 17

6. Peculiar secretions- Colouring matter. Threads. Light.

Air. Pearls, 19

7. Generative organs, 19

8. Condition of the Mollusca. Residence. Torpidity. Qui-

escence, 20

CHAPTER II.

PROGRESS or THE SCIENCE. SYSTEMS OF ARRANGEMENT.

1. Systems constructed from circumstances connected with the

characters of the Shell. Aristotle. Linnaeus. Bosc. Writ-
ers on microscopic shells, 26

2. Systems constructed from circumstances connected with the

Habits of the Animal. Lister. Sibbald. D'Argenville.
Schroter ~ 33

3. Systems constructed from circumstances connected with the

Form and Structure of the contained animal- Adanson.
Muller. Poli. Cuvier, 35

IV CONTENTS.

Page.

4. Mixed Systems. Lamark, 42

5. Value of the characters employed. Valves of the shell.

Canaliculated, dextral, operculated, pillared, multilocular,
free, gaping, equivalve shells. Muscular impressions.
Marginal impression. Ligament. Teeth. Borers, £9

6. Review of the Linnsean genera, 75

CHAPTER III.

SYSTEMATICAL DISTRIBUTION or THE MOLLUSCA.

I. Mollusca Cephala.

1. Natantia. Cephalopoda. Cuttle Fish. Nautilacea. Se-

piacea. Pteropoda. Limadna. Clio, J19

2. Gasteropoda. Pulmonifera. Terrestrial. Aquatic.—

Branchifera. Branchiae external. Branclda internal, 1 44

II. Mollusca Acephala.

1. Conchifera. Brachiopoda. Lingula. Terebratula. Bi-

valvia. Pectenidae. Ostreadce. Mytilida, 186

2. Tunicata. Dichitonida- Ascidia. Pyrosoma. Mo-

nochitonida. Salpa, 198

CHAPTER IV.

MOLLUSCOUS ANIMALS AS OBJECTS OF UTILITY.

1. Employed as Food. Oyster. Mussel. Cockle. Pearl. Dye, 217

2. Objects of Beauty. Preparation of Shells. Arrangement

in a Cabinet, 229

3. Mode of collecting Shells, 233

4. Fossil Shells. Their systematical, chemical, geognostic, and

geographical history, 235

MOLLUSC A.

THE Molluscous animals to which our attention is to be
directed in this article, formed, for a long period, two dis-
tinct objects of study. The naked species were considered
as constituting a particular group, to which the term MOL-
LUSCA was in a great measure restricted ; whilst the shelly
species attracted a large share of attention, being known as
objects of study by the term CONCHCXLOGY. Of late years,
however, this kind of systematical separation of the naked
and shelly species has been supported by few advocates,
whilst those who have urged the propriety of their union
have not only been numerous, but acknowledged as the
intelligent and successful investigators of nature. In con-
sequence of these changes, which have taken >place in pub-
lic opinion by the introduction of more correct notions of
the principles of classification, we have in [this edition of
our work, resolved on incorporating the articles MCOLLUS^A
and CONCHOLOGY, suppressing the latter term as unneces-
sary. Indeed, in a physiological point of view, there is no
definite boundary between the naked and the shelly species,
many of the reputed naked species having shells concealed
under their integuments, while in many of the shelly species
the solid plate or shell can only be reached by removing

2 MOLLUSCA.

the surrounding soft or fleshy matter. But the propriety
of abandoning the old divisions will become sufficiently
obvious, when we consider that all the species belong
to one group in the invertebrate class of animals ;
that the organs of the species have many points of
resemblance ; and that although differences prevail in
the character of the protecting covering, the gradations
from one condition of the integuments to another, are
too minute, in many cases, to admit of precise limits being
fixed. We shall therefore consider shells as peculiar mo-
difications of the external coverings of certain species, and,
in this subordinate character, incorporate the naked and
shelly species ; having recourse to the integuments, how-
ever, in connection with the other organs, in the distribu-
tion of the genera and other divisions of the class now
denominated MOLLUSCA.

In treating of this extensive division of the invertebrate
animals, we shall confine our remarks to a general view of
their physiology, taking notice of the peculiarities of their
forms, organs, and functions. This will prepare us for a
condensed view of the progress of the science, in reference
to systematical arrangement, and the illustrations of the
characters of those divisions or groups into which the spe-
cies may be distributed, whether for assisting the student
in his labours of investigation, or for facilitating the judici-
ous disposition of the established truths of the science. We
shall then advert, in the last place, to molluscous animals
as objects of utility. The limits of the article will unavoid-
ably restrict us to a very brief exposition of the various
subjects connected with this very extensive department of
natural history.

MOLLUSC A,

CHAPTER I.

PHYSIOLOGY.

Molluscous animals exhibit very remarkable differences,
both in their form and in the number and position of their
external members. Neither head nor foot can be observed
in some species ; the principal organs being enclosed in a
bag pierced with apertures for the entrance of the food, and
egress of the excrementitious matter. In others, with an
exterior still remarkably simple, cuticular elongations,
termed Tentacula> surround the mouth, and a foot, or in-
strument of motion, may likewise be perceived. This last
organ is in some free at one extremity, in others attached
to the body throughout its whole length. In many species
there is a head, not, however, analogous to that member in
the vertebral animals, and containing the brain and organs
of the senses, but distinguished merely as the anterior ex-
tremity of the body, separated from the back by a slight
groove, and containing the mouth and tentacula.

In many of the animals of this division, the different

MOLLUSCA

members of the body are in pairs, and are arranged, in re-
ference to a mesial plane, into right and left. In some, a
part only of the organs has respect to a mesial plane, other
parts being single, or in unequal numbers. In other species,
the organs, which are not in pairs, are arranged round a
central axis, and give to the external form a radiated ap-
pearance. But these characters are exceedingly variable
and uncertain, as indicating the limits of particular tribes ;
since, in different parts of the same animal, modifications of
all these forms may be readily distinguished.

The skin of molluscous animals is more simple in its
structure than the same organ in the vertebral animals.
The cuticle is here very distinct ; and, as in other classes,
it is thick and coarse where much exposed, but thin and
delicate in its texture where it lines the internal cavities.
A mucous web may be detected in the cuttle fish and slug,
but of great tenuity. The corium is destitute of a villous
surface ; and on its central aspect it is so intimately united
to cellular substance, that its fibrous structure can scarcely
be distinguished. The muscular web may, in general, be
readily perceived. Its fibres proceed in various directions,
according to the kind of motion to be executed, and extend
or corrugate the skin at pleasure.

The appendices of the skin in this class of animals ought
to be carefully studied, as they furnish the most obvious
marks for distinguishing species, and for constructing divi-
sions in their systematical arrangement. The appendices
of the cuticle are few in number, and perhaps ought to be
considered as limited to hairs. These, in some species,
invest the surface regularly and closely, and may be ob-
served on those which live on land, as well as those which
reside in water. In some cases the hairs may be considered

MOLLUSCA. 5

as united, and forming continuous crusts or ridges. These
hairs, as well as the cuticle, are liable to be worn off, and
in some places can seldom be perceived, unless in early
age.

The most important appendix to the skin, for such it
must be considered, appears to be the shell. This part is
easily preserved, exhibits fine forms and beautiful colours,
and has long occupied the attention of the conchologist.
The matter of the shell is secreted by the corium, and the
form which it assumes is regulated by the body of the ani-
mal. It is coeval with the existence of the animal, and
appears previous to the exclusion from the egg ; nor can it
be dispensed with during the continuance of existence.
The solid matter of the shell consists of carbonate of lime,
united with a small portion of animal matter, resembling
coagulated albumen.

The mouth of the shell is extended by the application of
fresh layers of the shelly matter to the margin, and its thick-
ness is increased by a coating on the inner surface. These
statements are abundantly confirmed by the observations of
Reaumur, (Memoir es de V Academic des Sciences, 1709)>
whose accurate experiments have greatly contributed to the
elucidation of conchology. If a hole be made in the shell
of a snail, and a piece of skin so glued to the inner margin
as to cover the opening, the shelly matter will not ooze out
from the broken margin of the fracture, and cover the out-
side of the skin, but will form a coating on its inner sur-
face, thus proving it to have exuded from the body of the
animal. When a portion of the mouth of the shell of a
snail is broken off, and a piece of skin glued to the inner
margin, reflected outwardly, and fixed on the body of the
shell, the defective part is again supplied, and the matte?

MOLLUSCA.

added to the inner surface of the skin, thus leaving the in-
terposed substance between the new formed portion and
the fractured edge. Similar experiments, repeated on a
variety of shells, both univalve and bivalve, by different
naturalists, leave no room to doubt that shells increase in
size by the juxtaposition of shelly matter from the common
integuments.

Each calcareous layer is more or less enveloped in the
animal matter which we have already stated as being pre-
sent ; so that the different layers of successive growth may,
by various processes, be distinctly exhibited. If the shell
has been exposed for a short time in the fire, the animal
matter will appear charred, and its black colour, contrasted
with the white earthy matter, will indicate the arrangement
of the different strata ; in the same manner as the ivory
and enamel of a tooth can be distinguished, when subjected
to similar treatment. The same satisfactory results may
be obtained by a different process. If the shell be steeped
in weak muriatic acid, the earthy matter will be dissolved,
and the flakes of albumen will remain as the frame-work
of the edifice.

The layers of growth may often be distinguished on the
surface of the shell, in the form of striae or ridges, more or
less elevated, but parallel to" the margin of the aperture.
Other inequalities may likewise be observed on the surface,
at right angles to the layers of growth, such as ridges,
knobs, and spines. These last derive their origin from the
inequalities of the skin on which they have been moulded.

In some univalve shells, the layers of growth parallel to
the opening cannot be discerned ; when exposed in the fire,
there is little darkening of colour ; and when dissolved in
acids, but a feeble trace of animal matter remains. In the

MOI/LUSCA. 7

fire, these shells crack in various directions, but exhibit no
trace of a scaly structure. By careful management with
the file, the shell may be separated into a central layer
contiguous to the skin, and a peripheral layer, both similar
in structure, though frequently differing in colour. The
shells exhibiting such characters have been termed porcel-
laneous, from their dense structure, and the fine polish
which their surface presents. The formation of shells of
this kind must take place in a different manner from those
of the first kind which we have noticed.

If we attend to the form of a young shell belonging to the
genus cypraea of Linnaeus, we may perceive that an addition
of shelly matter to the margin of the aperture, in the man-
ner in which it is applied in other shells, would not enlarge
the cavity, but completely close the aperture. The increase
of the shell, (accompanied with a corresponding increase of
its inhabitant), must take place, therefore, either by ab-
sorption of the accumulated shelly matter of the mouth, and
an elongation in the direction of the greatest curvature of
the shell ; or the old shell must be thrown off, and a new one
produced, suited to the size of the animal. The former sup-
position has not been entertained, the latter is now generally
received by naturalists, though there are a few individual^
unwilling to adopt such a view of the matter. The inner
coat of such shells appears to be a transudation from the
body of the animal, and the outer one to be laid on the sur-
face by the loose reflected lobes of the cloak. In many other
shells, portions of matter, more compact than the other parts,
may be observed spread on the pillar, and applied to the
margin of the mouth by a similar process. Mr. Platt, in
support of Reaumur's opinion, that shells are formed by jux-
taposition, against the objections of Mr. Poupart, (PhiL

MOL.LUSCA.

Trans, vol. liv. p. 43), erroneously considers the different
sizes of the cypreae as depending on the thickness of the
shell increasing according to age, without admitting a cor-
responding increase of the dimensions of the contained ani-
mal, or cavity for its reception.

The shells of the first kind which we have noticed, from
being formed of cones or layers applied to the inner edge of
the margin, and extending beyond it, have an imbricated
structure. Those of the second kind, consisting of layers
regularly superimposed, have consequently a laminated
structure ; but between the two kinds there are numerous
intermediate links, formed by a combination of the two pro-
cesses.

In some cases, the hard parts of the skin are not entitled
to the appellation of shell, but may rather be considered as
horn. Such are the coverings of the mandibles of the cut-
tle fish, the branchial lid of the aplysia, and the operculum
of the welk. The two last appendices, however, though
horny in some species, are shelly in others.

The position of the shell, with respect to the constituent
layers of the integuments, exhibits very remarkable differ-
ences. In some it appears instead of a cuticle, or at least
without an external membrane investing it. In general,
however, it occurs between the cuticle and the skin ; a po-
sition which induced Cuvier (Lee. cFAnat. Comp. xiv. 11.)
to consider it as analogous to the mucous web of the verte-
bral animals. Its intimate connection with the muscular
system of the animal, and the protection which it affords, .
seem adverse to such a conclusion. In many species the
testaceous substance occurs in folds of the corium, or insert-
ed in its substance. In this position it never acquires the
solid texture which shells exposed, or covered only by the

MOLLUSCA. 9

cuticle, exhibit. Those shells which are thus concealed
are in general white ; those which are more exposed are
frequently coloured. The colouring, however, does not de-
pend on the direct exposure to the light, as some have im-
agined, for many shells which are destitute of a cuticle are
white, while many of those covered by a dense cuticle are
finely variegated beneath.

Between the skin and the shell neither vessels nor nerves
have been traced ; and the manner in which the latter is
formed, forbids us to expect their existence. Yet the shell
cannot be considered as dead matter, so long as it remains
in connection with the living animal. In those animals in
which the shell is external, there are muscles which connect
the animal with its internal surface, and the bond of union
being a substance soluble in water, the muscle can be de-
tached by maceration. The analogy between shell and
bone is here obvious, although in the one case the connec-
tion between the muscle and the bone is permanent, in the
other, between the muscle and shell, temporary, or frequent-
ly changed during the life of the animal. But the vitality
of the shell, if I may use the expression, is demonstrated,
from the changes which it undergoes when detached from
the animal: the plates of animal matter harden: the epi-
dermis dries, cracks, and falls off; and in many cases the
colours fade or disappear. We confess ourselves unable to
point out the means employed by the animal to prevent
these changes from taking place, by any process similar to
circulation. The difficulty, however, is felt in contem-
plating the functions of hairs, nails, and feathers, in verte-
brated animals.

When the shelly covering consists of two or more pieces,

10 MOLLUSCA.

they are joined together, as the articulated bones in the
higher classes of animals, by ligaments. These, in some
cases, are of great thickness and strength, and, in con-
sequence of their elasticity, assist in the motion of the dif-
ferent parts.

In the molluscous animals the skin secretes a viscous,
adhesive substance, differing according to the medium in
which the animal resides, but in all cases calculated to re-
sist its influence. It is probably owing to the lubricating
agency of this secretion, that both the cuticle and shell are
preserved from decomposition. The skin likewise secretes
the colouring matter by which the shells are variegated.
The glands from which it proceeds vary much in different
individuals, and even in the same individual in different pe-
riods of growth.

The characters furnished by the skin and its appendices
are extensively employed in the systematical arrangement
of molluscous animals. Nearly all those characters which
distinguish the species, and many of those on which genera
are established, are derived from the form of the shell, the
tentacula, or the colour. This last character, however, is
one on which little dependence should be placed.

There is nothing peculiar in the MUSCULAR SYSTEM of this
class of animals. Where the* muscles are inserted in the
skin, as is usually the case, that organ is in some cases
strengthened by condensed cellular substance, and even ac-
quires a leathery density.

Molluscous animals preserve themselves in a state of rest,
chiefly by suction and cementation. The organ which acts
as a sucker, is in some cases simple, soft, and muscular, sis
the foot of the snail, while in others it is compound, and

MOLLUSCA. 1 1

strengthened internally by hard parts, as in the arms of the
cuttle-fish. The force with which some animals adhere is
very considerable, and is strikingly displayed, for example,
when we attempt to detach a limpet from the rock.

The rest, which is maintained by cementation, in some
cases depends on a glairy secretion, which glues the body
of the animal to the substance to which it is disposed to be
attached. By such an expedient, the shells of snails adhere
to rocks, stones, and plants. It is probable that the bivalve
shells of the genus Cyclas, which readily adhere to the side
of a glass, secure their temporary attachment by means of
their glutinous cuticle. In other animals threads are pro-
duced, termed a bi/ssus, from particular glands, and while
one extremity is glued to the rock, the other remains in
connection with the animal. But there is an attachment
more durable than any of these, which takes place in some
shells, they being cemented to rocks or stones by calcare-
ous matter, and retained in the same position during the
whole term of their existence.

The locomotive powers of the mollusca are confined to
creeping and swimming. The former action is performed
by alternate contraction and relaxation of the foot, or mus-
cular expansion, which serves as a sucker, and is analogous
to the motion of serpents. The motion of swimming is
executed either by the serpentine undulations of the foot
and the body, or by the action of tentacula, or expanded
portions of the integuments. Many species are aided in
swimming, by being able to vary the specific gravity of their
body at pleasure, and either rise or sink in the water as
circumstances may require. In some, as the Janthina, there
is a cellular organ peculiarly destined for this purpose, which
may be regarded as in some measure analogous to the air-

12 MOLLUSCA.

bladder of fishes. In all these exertions the progress of mol-
luscous animals is proverbially slow. Some bivalve shells
have the power of leaping, or shifting their position by a
sudden jerk, produced by shutting the valves rapidly. This
is strikingly displayed in the common scallop, and is less
perfectly exhibited in the river mussels. In a few instan-
ces, especially among the slugs, a thread is formed of the
viscous secretion of the skin, by which the animal is enabled
to suspend itself in the air from the branches of trees like
a spider.

Although the progressive motions of molluscous animals
are comparatively slow, the other muscular actions are exe-
cuted with ordinary rapidity. The irritability of some parts,
as the tentacula and branchiae, is so great, that the protect-
ing movements are executed almost instantaneously, and
the organs are contracted or withdrawn into the body. But
these rapid exertions are only called forth in the moments
of danger,

The characters furnished by the muscular system, are of
great value in the discrimination of species, and in the con-
struction of genera and higher divisions. They are inti-
mately connected with the habits of the animal, and merit
the attentive examination of the philosophical naturalist.

In the molluscous animals the NERVOUS SYSTEM is less
complicated in its structure than in the higher classes, and
the brain is not restricted in its position to the head. The
whole nervous system appears in the form of ganglia and
filaments. The principal ganglion, or the one to which the
term brain is usually applied, is seated above the gullet or
entrance to the stomach. It sends out nerves to the parts
about the mouth, the tentacula, and the eyes. It may be
considered as analogous to the cerebrum of the vertebral

MOIXUSCA. 13

animals. From this ganglion proceed two filaments, one
on each side, which in their descent inclose the gullet, and
unite underneath to form a second ganglion. From this
last, which has been compared to the cerebellum, numerous
filaments are likewise distributed to the parts around the
mouth, and to the other regions of the body. These fila-
ments in some cases again unite, and form subordinate gan-
glia. In many cases the brain and ganglia are of a reddish
colour, and granulated structure, while the nerves which
issue from them are white and uniform, as in the genus Ap-
lysia. The covering of the first ganglion, which is analo-
gous to the dura mater, does not adhere to it closely, but
leaves a space filled with loose cellular matter. The tu-
nics of the nerves are equally detached ; and as they can
be inflated or injected readily, some have been led to sup-
pose that the nerves were hollow, and others, that the tunics
were the vessels of the lymphatic system.

The organs of perception common to the higher classes
x>f animals, do not all exist in an obvious manner amongst
the mollusca. The touch, that universal sense, is here dis-
played in many cases with great delicacy ; and the tenta-
cula, and the other cuticular elongations which we have al-
ready referred to, contribute to augment its resources. The
sense of sight is by no means universally enjoyed by the in-
habitants of this class. In a few species, the eye is con-
structed on the plan of the same organ in the vertebral ani-
mals. In general, however, it appears only as a black point,
the peculiar functions of which can only be inferred from
analogy. In many species there is no trace of an eye, con-
sequently they cannot possess that varied information which
the others derive from that organ. Where eyes exist in
this class, they are uniformly two in number. In one tribe

1 4 MOLLUSCA.

only, namely the cuttle-fish, the rudiments of the organs of
hearing have been detected. The organs adapted to smell-
ing cannot be exhibited, but the existence of the sense is
demonstrated by the facility with which molluscous animals
discover suitable food, when placed within their reach.
The sense of taste appears to exist, but it is difficult to point
out the particular parts of the mouth fitted for its residence.
As, however, particular articles of food are selected in pre-
ference to others, it may be concluded from analogy that
taste regulates the choice.

In the classification of the mollusca, the characters fur-
nished by the nervous system, from the difficulty of their
detection and exhibition, have never come into use. But
those furnished by the organs of preception are highly priz-
ed. Of these, the eye is the most obvious and constant.
It varies in position in different species ; but, among indi-
viduals of the same species its characters are constant.

In the cutaneous, muscular, and nervous systems, traces
of a general plan may be observed, according to which they
have been constructed in the different tribes. In the or-
gans which remain to be considered, there is less uniformity
of structure, each family almost being constructed accord-
ing to a model of its own.

The time when molluscous animals feed has not been
carefully attended to. Those which live in the water are
beyond the reach of accurate observation. Those that re-
side on land usually shun the light, and creep forth in the
evenings to commit their depredations. During warm, dry
weather, they stir not from their holes.

The animals under consideration, feed equally on the
products of the vegetable and animal kingdom. Those
which are phytivorous appear to prefer living vegetables, and

MOLLUSCA. 15

refuse to eat those which are dried. We are not aware that
putrid vegetable matter is consumed by them, although
many of the snails and slugs are found under putrid leaves
and decayed wood. In these places there is shelter from
the sun, together with dampness, so that it is difficult to de-
termine, whether they sojourn in an agreeable dwelling, or
a well-stored larder. Those mollusca which are carnivo-
rous, prey on minute animals in a living state, and many of
them greedily attack putrid matter.

The means employed to bring the food within the reach
of the organs of deglutition, are exceedingly interesting,
both on account of their variety and success. Some are
provided with tentacula for securing their prey, and con-
veying it to their mouth, as the cuttle-fish ; others protrude
a lengthened probosis, or an extended lip or tongue, as the
limpet, and thus bring their food into the mouth. By many,
however, which are fixed to the same spot during the continu-
ance of existence, or only capable of very limited locomotive
power, successful efforts are made to excite currents in the wa-
ter, whereby fresh portions of it are brought in contact with the
mouth, and its animal or vegetable contents separated.
Where part only of any kind of food is taken into the mouth
at once, the lips are possessed of sufficient firmness to cut
off the requisite portions, or there are corneous mandibles
to perform the office.

In the mouth, there is scarcely any process performed
analogous to that of mastication, in the higher orders of ani-
mals3 When the food is in the mouth, or entering into the
gullet, it is mixed with saliva, as in the more perfect ani-
mals. The salivary glands in which it is secreted, are in
general of considerable size, divided into lobes, and, in some
cases, separated into distinct masses. In many species the

16 MOLLUSCA.

existence of a gullet is doubtful, as the food seems to enter
the stomach immediately ; while, in others, there is a por-
tion of the intestinal canal which has some claim to the de-
nomination.

The stomach, in many instances, is membranaceous, and
can scarcely be distinguished from the remaining portion of
the intestinal canal. In some cases, however, it is strong
and muscular like the gizzard of a bird, and even fortified
with corneous knobs for the reduction of hard substances.
In some species, the stomach opens laterally into the py-
lorus, and, in a few instances, possesses a spiral caecum
attached to it.

The liver is usually of very large dimensions, and seated
close to the stomach, which it, in many cases envelopes.
It is divided into many lobes, and receives numerous blood-
vessels. There is, however, nothing analogous to the vena
portarum of quadrupeds. The bile is poured, in some, into
the stomach, and, in others, into the pyloric extremity of
the intestine by different openings. There is no gall-blad-
der.

There is no division of the canal into small and large in-
testines, as in the higher classes ; or rather, among the mol-
lusca, the relative size of the different parts is reversed.
Here the pyloric extremity is usually the largest, while the
anal is more slender. The intestine, as in fishes, is short
in proportion to the length of the body, and in its course,
is subject to few turns. The anus, is, in some, placed on
one side of the body ; in others it is terminal, while in a few
it opens on the back.

The digestive system is thus more simple in its structure
than in the higher classes. It possesses neither pancreas,
spleen, nor mesentery. And, we may add, that the calls of

MOLLUSC A. 17

hunger are often at distant intervals, and the power of ab-
stinence very great.

The characters furnished by the digestive system are ex-
tensively used in the inferior divisions of molluscous ani-
mals. The form of the lips, the position of the mouth and
anus, and the structure of the stomach, deserve to be atten-
tively considered, as indicating the habits of the species.

CIRCULATING SYSTEM — The process by which the food
is converted into chyme, has not been satisfactorily traced,
nor has the existence of the lacteals for the absorption of
the chyme been demonstrated. In this class of animals the
veins seem to perform the offices both of lacteals and lym-
phatics. The blood is white, or rather of a bluish colour.
Its mechanical and chemical constitution yet remains to be
investigated.

The circulating system of molluscous animals, exhibits
very remarkable differences in the different classes. In all of
them, however, there is a systemic ventricle; but the other
parts of the heart are not of constant occurrence.

The circulating system furnishes few characters which
can be employed in systematical arrangements. The struc-
ture of the systemic and pulmonary vessels does not ap-
pear to be co-ordinate with any particular plan of external
configuration and manner, as we see in the case of the
pteropoda and gasteropoda. In these, the organs of circu-
lation are very much alike, while the external forms exhibit
very obvious differences.

The molluscous animals which respire by means of lungs
are few in number, and form a very natural tribe, which
Cuvier has termed gasterpodes pulmones. In them the res-
piratory organ is simple, consisting of a single cavity, on the

18 MOLLUSCA.

walls of which the extremities of the pulmonary artery are
spread. This cavity communicates externally by an aper-
ture which the animal can open or shut at pleasure.

The mollusca which breathe by means of gills, exhibit
very remarkable differences, in their number, structure, and
position. In some cases, there is a single cavity communi-
cating by an aperture, through which the water enters.
The walls of this cavity exhibit an uneven surface, dispos-
ed in ridges, which are the gills, and on which the pulmo-
nic artery is expanded. This structure exhibits itself in
the Gasteropoda peetini-branchia. In many cases the gills,
though seated in a cavity, like the former, and equally ex-
posed to the contact of the surrounding element, are two in
number, one on each side, as in the Cephalopoda. In the
Bivalvia, they are four in number, two on each side like
leaves, and extend the whole length of the body. In these,
the water is admitted at the pleasure of the animal.

The gills of other mollusca are seated externally, and
consist either of aborescent productions, or simple cuticular
elongations, within which the pulmonary artery terminates.
In some of these, as the Pteropoda, the branchial surface is
constantly exposed to the action of the surrounding water ;
whilst in others, the cuticular expansions, which are analo-
gous to gills, are retractile 'at the will of the animal. In
several examples, these cuticular elongations, which execute
the functions of respiration, are covered with moveable cilia,
well calculated to excite currents in the water, thus renew-
ing the portions applied to the surface.

By means of the characters furnished by the circulating
and respiratory systems, the molluscous animals may be
divided into several distinct classes. But as we shall em-
ploy these characters in the construction of the different

MOLLUSCA. 19

divisions to be employed, it is unnecessary, in this place, to
enter into their details.

PECULIAR SECRETIONS — The molluscous animals are con-
sidered as destitute of organs for the production of urine,
but they possess various organs for the secretion of peculiar
fluids or solids, some of which are useful in the arts.

The coloured fluid, which is secreted by the Cephalopo-
da and some of the aquatic gasteropoda, appears to consist
chiefly of a peculiar mucus, united to a peculiar pigment.
The animals which furnish this secretion, eject it when in
danger or irritated, and thus envelope themselves in a dark
cloud, and elude the pursuit of their foes. A milky secre-
tion is poured forth over the surface of the skin of some
slugs when irritated. Other coloured secretions may like-
wise be detected in the mollusca, to which we shall after-
wards advert. The threadlike secretions, termed a tyssus,
with which some molluscous animals, especially among the
Conchifera, fix themselves to other bodies, appear to be of
an albuminous nature. A few species in this division have
the power of secreting a luminous fluid. Its nature, and the
organs in which it is elaborated, have not been investigated.
It is probable that some animals, as those which have the
faculty of raising or lowering themselves in the water, have
likewise the power of secreting air into those organs which
contribute to their buoyancy.

Morbid secretions likewise occur amongst the animals of
this division, chiefly, however, amongst the Conchifera.
The most important of these are pearls, so much prized as
ornaments of dress.

The organs of generation, some of which will be noticed
afterwards in detail, furnish many important characters for

20 MOLLUSC A.

classification. The external openings are those which are
detected with the greatest facility, but the structure of the
internal organs exhibits more varied and discriminating
marks.

CONDITION OF THE MOLLUSCA — Molluscous animals, in
reference to their condition, are divided, according to the
•situation in which they reside, into three groups, which
•may be termed terrestrial, fluviatile, and marine. Those
that inhabit the land belong exclusively to the gasteropoda.
Among these, some prefer open pastures, others the rub-
bish of old walls, while not a few reside in woods or among
•dead leaves and putrid plants. All the animals of this
group respire by means of a pulmonary cavity.

The fluviatile mollusca, or such as reside in fresh waters,
include not only many gasteropodous genera, but likewise
a few belonging to the Conchifera. Amongst these, some
breathe air by means of a pulmonary cavity, and come to
the surface to respire. Such species frequent the more
shallow ponds and lakes. Others, respiring by means of
gills, are less dependent on the shallowness of the water,
and consequently reside in different depths.

The marine mollusca include genera of all the classes.
Some burrow in the sand, of adhere to the rocks which are
left dry by the receding tide. These are termed littoral
species. Others, however, which have been denominated
pelagic, reside in the deep, and are seldom obtained but by
dredging, or when thrown ashore during storms.

The effect of temperature in regulating the distribution
of molluscous animals, has not been investigated with any
degree of care or success. Over the terrestrial and fluvia-
tile species, it probably exercises a very powerful control,

MOLLUSCA. 21

greatly limiting their geographical range. In proof of this,
it may be stated, that the south of France possesses several
species not to be found in England, whilst in England, there
are a few which have not been detected in Scotland. But,
among the marine mollusca, the influence of climate is not
felt in the same degree. Living in an element, the bulk
and motions of which guard it equally from the extremes of
heat or cold, these animals, like the sea-weeds, have a very
extensive latitudinal and longitudinal range. Thus, some
are common to Greenland and the Mediterranean, others to
Britain and the West Indies. The mollusca of the tropical
seas, however, differ widely as a whole from those of the
temperate regions. Some of the forms appear to be peculiar
to warm regions, and, in general, the intensity of colour de-
creases as we approach the poles. But as there have been
few cultivators of this branch of science, the geographical
distribution of the species has been but imperfectly explor-
ed. Few parts of either England or Scotland have been
surveyed by the eye of the helminthologist, so that many
species, the range of which is considered as limited, may
soon be found to be extensive.

If the observations are few and imperfect, which have
been made on the influence of temperature, in regulating
the physical distribution of mollusca, we are still in greater
ignorance with regard to the power of habit. In the flcetz
rocks, the relics of marine and fluviatile mollusca are found
mixed in the same bed. This circumstance gave rise to the
inquiry, how far the mollusca of fresh water can be habitu-
ated to sea- water, and vice versa. In the account of the
proceedings of the National Institute of France, for the
year 1816, it is stated, that M. Beuchant, professor at Mar-
seilles, has directed his attention to this subject. He found,

22 MOLLUSCA.

that all these animals die immediately, if we suddenly
change their place of abode ; but that, if we gradually in-
crease the proportion of salt in the water for the one set,
and diminish it for the other set, we can, in general, accus-
tom them to live in a kind of water which is not natural to
them. He found, however, some species which resisted
these attempts, and which could not bear any alteration in
the quality of the water in which they reside. Before much
confidence can be placed in the accuracy of these results,
it would be desirable that the experiments were repeated
and varied by other observers. There are, indeed, many
sources of error to be guarded against. When we change
animals from fresh to salt water, or from salt water to fresh,
we must necessarily derange their motions, by compelling
them to reside in a medium of a different degree of density
from the one in which they have been accustomed to dwell,
and to which the arrangement of the different parts of the
body is adapted. By such a change of place, it would be
difficult for those which breathe air to come to the surface,
and descend again in their new situation. In those with
gills, the application of a new kind of fluid to the surface of
such delicate organs, would considerably influence the func-
tion of respiration. The change of situation would like-
wise be accompanied by a corresponding change of food,
and consequently, not merely the organs of locomotion and
respiration, but likewise those of digestion, would suffer a
derangement in their operations. We know that the power
of suffering in the animals of this class is very great, and
that they survive, though sadly mutilated. Some of the
snails will live in a quiescent state for years, without food,
and almost without air. Unless, therefore, the animals
subjected to these experiments of a change of situation, have

MOLLUSCA. 23

been observed to thrive on the food which it spontaneously
yields, to execute their accustomed motions, and above all,
to propagate their kind, we shall be disposed to conclude,
that patient suffering has been mistaken for health and
vivaciousness for the power of accommodation.

The influence of the seasons, in regulating the motions
and habits of molluscous animals, has been but little attend-
ed to. Those which live in the water, avoid the effects of
low temperature, on the approach of winter, by retiring to
the deeper parts of the lakes or rivers in which they reside.
This migration, however, does not, in many cases, furnish
the requisite security, so that they betake themselves to
burrowing in the mud in which they repose until increasing
warmth invites them to return to the open water.

Among the naked terrestrial mollusca, it may be observ-
ed, that they burrow in holes of the earth, under the roots
of trees or among moss, and there screen themselves from
sudden changes of temperature, and appear to spend the
winter in a state of torpidity.

The different kinds of shelly mollusca which inhabit the
land, such as those belonging to the genera Helix, Buli-
mus, and Pupa, not only retire to crevices of rocks and other
places, for safety in the winter season, but they form an
operculum or lid for the mouth of the shell, calculated to
exclude the access of the air, and by the intervention of
which they likewise adhere to the wall of their dwelling. A
rise of temperature, however, especially if accompanied by
moisture, excites their revival and motion, and the lid be-
comes detached. If we bring, for example, the Helix ne-
moralis, from its cold abode, and in an apparently torpid
state, with the mouth of its shell closed by the lid and ad-
hering to a stone, into a warm apartment, it will speedily

24 MOLLUSCA.

revive, especially if it be moistened with a little water,
hurst open the lid and begin to crawl. If the animal be
again exposed to a low temperature, it again secretes ma*-
terials for a new lid, and speedily returns to its slumbers or
inactivity. The first formed opercula, in these animals, al-
ways contain a considerable proportion of carbonate of lime,
a material which is found in smaller quantity in those of
after formation. If the animal has revived frequently dur-
ing the winter, the last formed opercula will be observed to
consist chiefly of animal matter, and to be very thin. The
first formed winter lid of the Helix Pomatia is of the con-
sistence of card-paper.

All the land shelly mollusca appear to have the power of
passing into a state of quiescence resembling torpidity, at
pleasure, and independent of low temperature. Thus, even
in midsummer, if we place in a box specimens of the Helix
hortensis, nemoralis aut arbustorum, without food, in a day
or two they form for themselves a thin operculum, become
attached to the side of the box, and assume a dormant con-
dition. In this state of apparent torpidity they may be kept
for several years. No ordinary change of temperature pro-
duces any effect upon them, but they speedily revive if
moistened or plunged in water. Even in their natural
haunts, they are often found in this dormant state, during
the summer season, especially when there is a continued
drought. Thus the Helix nemoralis may frequently be
observed several feet from the ground, and attached to the
stem or leaves of plants, with the mouth of the shell closed.

But it is not drought which influences these terrestrial
shelly mollusca to assume this quiescent state. The Sue-
cinea putris, a species in ordinary cases delighting in mois-
ture, may readily be observed during summer in a dormant

MOLLUSCA. 25

state, high on the leaves of the Water Flag, having retired
from the moisture below. In the same manner, and from
causes equally obscure, some of the marine shelly mollusca,
as the Limpet, Periwinkle, and Trochus, may be observed
in a quiescent state on the rocks, above the reach of the
tide. A shower, however, in general excites the Succinea,
as well as the Limpets and Periwinkles, to motion,

26 MOLLUSCA.

CHAPTER II.

PROGRESS OF THE SCIENCE.

NATURALISTS have pursued a variety of methods in their
examination of this important branch of Zoology, and have
proposed systems of arrangement founded on very different
principles, and marking different epochs in the science. In
the methodical distribution observed by some, the form of
the shelly covering has been exclusively attended to, while
the organization of the animal itself has been overlooked, or
even disregarded. A few have made the habits of the ani-
mal, the groundwork of their system. Others have passed
over the characters exhibited by the forms and structure of
the shell, and have confined their attention exclusively to
the form and structure of the contained animal. Lastly,
there have been a few, who, embracing all the circumstan-
ces connected with the shellr the animal, and its habits, have
constructed systems at once natural and convenient. In the
following sections we propose to consider these four classes
into which the cultivators of this department of science may
be distributed.

SECT. I. — Systems constructed from circumstances connect-
ed with the characters of the Shell.

The arrangement of the testaceous mollusca, according

MOLLUSCA. 27

to the different forms of the shell, is unquestionably the most
obvious and the most ancient method. It was first employed
by Aristotle, the father of natural history, and even in the
present day its admirers are warm in its praise. It is with
great propriety termed the artificial method, because the
characters employed have but a remote relation to the more
important functions of the animal. This eminent philoso-
pher had the merit of forming the great divisions of unival-
ves and bivalves. He likewise separated the turbinated uni-
valves from such as have but an imperfect spire, and formed
many genera, or rather families, still retaining the names
which he imposed.

The progress of the study of the shelly mollusca (the
naked kinds being in a great measure neglected,) made very
little progress for many ages after Aristotle had published
his method of arrangement. Indeed, the first work of this
sort which claims attention, is the Dictionarium Ostracolo-
gicum of Major, which was published in 1675. To him we
are indebted for the threefold division of shells into uni-
valves, bivalves, and multivalves, and for an explanation of
the terms then employed by conchologists.

In the same career, but with more brilliant success, Lan-
gius followed, and, in 1722, published his Methodus Nova
Testacea Marina in suas Classes, Genera et Species distri-
buendi. The following character is given of this work by
the intelligent and industrious authors of the Historical Ac-
count of Testaceological Writers. (Linn. Trans, vol. vii.
p. 156.) " After having noticed a multitude of mere de-
scribers, we now come to an author who is not undeserving
of the title of a scientific one, and whose system, so far as
marine testacea are concerned, (and of these alone he treats)
certainly glances at the great clue to simplicity, which was

MOLLUSCA.

afterwards so successfully and admirably seized by the great
reformer of natural history in general." But Langius de-
serves more praise than is here bestowed upon him. Be-
fore his system appeared, the characters of the genera de-
pended principally on the outline, and were of uncertain ap-
plication. He remedied the defect, by directing the atten-
tion of conchologists to the form of the mouth in univalves,
and to the structure of the hinge in bivalves. Among the
former, he constituted subdivisions of those ore super ius
aperto, ore superius in canaliculum abeunte, and ore su-
perius clauso. Amongst the latter, the circumstance did not
escape him, that some of these shells are eguivalve, others
inequivalve; some equilateral., others inequilateral. Hence
he may be considered as the founder of the inferior divi-
sions of the artificial method, and as having furnished, to
modern conchologists, many useful hints, of which they have
availed themselves, without, however, acknowledging their
origin.

Another important improvement was effected by Brey-
nius in his Dissertatio Physica de Polythalamiis, 1732, in
4to. This consisted in separating from the ordinary uni-
valves, such shells as possess a cavity divided by partitions
into several compartments, and in forming them into a di-
vision, which he termed Polythalamium. These shells are
now called Multilocular.

The system of Tournefort, which was published by Gu-
altieri, in his Index Testarum Conchyliorum quce adservan-*
tur in MUSCEO Nicolai Gualtieri, Philosophi et Medici, Flo-
renting 1742, well deserves an attentive perusal. In his
observations on the bivalves, now denominated the acephal^
ous mollusca, he drew the attention of conchologists to an
important character, and one of easy application, having oh-

MOLLUSCA. 29

served that, in some genera, the valves do not close or unite
all round, but that, at certain places, the shell remains in
part open. Such shells, in modern language, are said to
gape.

The system of the celebrated Linnaeus, which ought now
to be mentioned, is too well known in this country to de-
serve particular notice. In many of the other departments
of Zoology he effected the most important alterations ; but
his attempts to reform the science of conchology, were far
from being equally successful. To the subject he never
was much attached, nor does he appear to have availed him-
self sufficiently of the labours of those authors whom we
have mentioned, and of others who preceded him. The
primary divisions which he employed, were those which
Major had established, and his genera, with a few excep-
tions, were those in common use. His merit as a concho-
logist rests entirely on the accurately defined terms, the
concise specific characters, and the convenient trivial
names which he employed and introduced. The particu-
lar consideration of the Linnaean genera, and the subse-
quent changes which have been introduced into them, will
form the subject of a separate section.

For some time after the publication of the Systema Na-
turce, the illustrious Swede enjoyed a very dangerous repu-
tation. All his arrangements were regarded as of such high
authority, that it was considered as impious to attempt to in-
troduce any change ; so that conchology, and along with it
the study of the mollusca, according to the artificial method,
remained a long time stationary. At last in France, a coun-
try which refused to submit to the fetters of the Linnaean
school, several new systems were proposed, which had for
their object the restoration of those well-founded genera,

30 MOLLUSCA.

which Linnaeus, in his too great desire to simplify, had sup-
pressed, and the accommodation of the divisions of the
science to those new relations which a more extensive know-
ledge of species had discovered. In this number Bosc stands
eminently conspicuous. In his work entitled Histoire Na-
turelle des Coquilles, des Vers et des Crustacea, and in the
conchological articles of the Dictionnaire d> Histoire Na-
turelle, he has favoured the world with a detail of his sys-
tem, the outline of which we shall here present to our rea-
ders :

I. COQUILLES MULTI VALVES.

1. Les unes n'ont point de charniere.

Oscabrion, Anatif, Balanite.

2. Les autres en ont une.

Pholade, Taret, Fistulane, Anomie, Calceole.

II. COQUILLES BIVALVES.
i. Equivalves.

1. A charniere sans dents.

Pinna, Modiole, Moule, Anodonte.

2. A charniere garnie des dents.

A. A une dent.

Mulette, Crassalette, Paphie, Mactre.

B. A deux dents.

a. Simple. Trigonie, Tridacrie, Hyppope, Cardite, Lu-
traire, Petricole, Venericarde, Solen, Capse, Sanguine -
laire.

b. Avec des surnumeraires. Isocarde, Donace, Cyclade,
Telline, Venus.

C. A quatre dents.
Bucarde, Mere trice, Lucine.

MOLLUSCA, 31

D. A beaucoup de dents.

Nucule, Petoncle, Arche, Cucullee.
ii. Inequivalves.

1. A charniere sans dents.

Acarde, Radiolite, Vulselle, Marteau, Huitre, Avicule,
Peigne, Lime, Houlette, Cranie, Hyale, Linqule.

2. A une dent.

Came, Corbule.

3. A deux dents.

Spondyle, Plicatule, Placune, Pandore, Terebratule, Cal-
ceole-

4. A plusieurs dents.

Perne.

III. COQUILLES UNIVALVES.

i. Uniloculaires.

1. Sans spirale.

A. En Calotte.
Patelle, Oscane.

B. En Tube.

Vermiculaire, Silicaire, Arrosoir.

2. En spirale.

A. L'ouverture entiere et sans canal a sa base.
Carinaire, Haliotide, Sigaret, Stomate, Argonaute, Con-
el lolepas, Nerite, Natice, Helecine, Hellice, Volvaire,
Bulle, Jacinthe, Turritelle, Cyclostome, Bulime, Sabot,
Toupie.

B. L'ouverture echancree et canaliculee a sa base.
Cerite, Pyrule, Rocber, Rostelaire, Strombe, Buccin,

Casque, Vis, Pourpre, Volute, Ovule, Tarriere, Porce-
laine, Cone.

32 MOLLUSCA.

ii. Multiloculaires.

Nautile, Orbulite, Ammonite, Planulite, Camerine, Rotn-
lite, Turrilite, Baculite, Spirule, Orthocere, Hippurite,
Belemnite.

In this system which we have exhibited, the arrangement
is more methodical, and the genera are more definite, than
in the Linnaean system. It unquestionably holds the first
rank in the modern artificial methods.

There is a class of writers whose labours deserve some
notice in this place. We allude to those who have devoted
their attention to the very minute shells, so common among
the sand on every sea-coast. These are too small to be
examined by the naked eye, and from the instrument em-
ployed in their investigation, they are usually termed Mi-
croscopic Shells. Plancus, in his work, De Conchis Arimin-
ensibus minus notis, published in 1739, may be considered
as the first who drew the attention of conchologists to these
nearly invisible objects. J. F. Hoffman, in his Dissertati-
uncula de Cornu Ammonis nativo Littoris Bergensis in
Norvegia, published in the Transactions of the Electoral
Academy ofMentz, 1757, and in his essay de Tubulis Ver-
micularibus Cornu Ammo?iis referentibus, ibid. 1761, made
us acquainted with various species of minute nautili pro-
duced on the northern shores. Nor did those discoveries
fail to excite interest in this -country. Boys and Walker
devoted their attention to the subject, and gave to the world
the result of their labours, in a thin quarto, entitled, Tes-
tacea Minuta rariora nuperrime detecta in arena littoris
Sandvicensis, London, 1784. Other observers, equally ar-
dent and successful, have increased our knowledge of the
forms of these minute bodies, particularly Soldani, who, in
his Testaceographia ac Zoophytographia parva et micros-

MOLLUSCA. 33

copica, 1789 and 1795, exhibited many figures of the mi-
nute shells of Portoferrara, &c. Mr. Adams likewise de-
scribed the minute species which he observed on the coast
of Pembrokeshire, in the third and fifth volumes of the
Transactions of the Linncean Society of London, and other
species of British growth have been investigated by the au-
thor of Testacea Britannica. We shall close this list with
noticing the Testacea Microscopica aliaque minuta ex yett-
cribus Argonauta et Nautilus ad Naturam Picia et De-
scripta, Vienna, 1798. It is the joint production of L. A.
Fichel and J. P. C. A. Moll, and merits an attentive perusal.

We a"re aware that such microscopic investigations are
regarded by some conchologists as useless, so that the mi-
nute species are excluded from their systems. But it is
surely a strange method of proceeding in natural history, to
judge of the merits or importance of species from their size.
It is true that we are still ignorant of the inhabitants of
those shells, and may long continue to be so ; but our pre-
sent knowledge of these shells has enabled us to fill up many
blanks, to perceive several new relations, and even to draw
some important conclusions.

That this sort of inquiry has in many instances been in-
judiciously conducted, all who are acquainted with the sub-
ject must admit. Due care has not been taken to distin-
guish these minute testacea from the fry of the larger shells,
so that the number of species has been very injudiciously
multiplied. These remarks apply to several figures of
Walker, and to a still greater number of those of Adams.

SECT. II. — Systems constructed from Circumstances con-
nected with the Habits of the Animal.

The authors of the preceding class have laboured to bring

34 MOLLUSCA.

to perfection the artificial system of conchology, and have
formed their arbitrary characters, independent of the habits
of life of the contained animal. But the naturalists whom
we have now to consider, have traced these animals to their
lurking places, and arranged them according to the situation
in which they reside, instead of the forms which they ex-
hibit.

At the head of this class of conchologists, Dr. Martin Lis-
ter stands pre-eminently conspicuous. His great work, en-
titled Historia sive Synopsis Methodica Conchylwrum, was
begun in 1685, and completed in 1692. It will long remain
a monument of the extensive information and unwearied
diligence of its author. The following synoptical view of
the work will enable our readers to comprehend its plan ; the
original should be consulted with care.
Lib. i. De Cochleis terrestribus.
Pars 1. De Buccinis terrestribus.
Pars 2. Cochleae nudae terrestres Limaces quibusdam

dictae.

Lib. ii. De Turbinibus et bivalvibus aquae dulcis.
Pars 1. De Turbinibus.
Pars 2. De Testaceis bivalvibus fluviatilibus.
Lib. iii. De Testaceis bivalvibus marinis.

Pars 1. De Testaceis bivalvibus, imparibus testis.
Pars 2. De Testaceis bivalvibus, paribus testis.
Pars 3. De Testaceis multivalvibus.
Lib. iv. De Buccinis marinis, quibus etiam vermiculi.

dentalia et patellae numerantur.

The plan followed by Sir Robert Sibbald in his Scotia
Illustrata is somewhat different from that of Lister. He
divides the Testacea into two classes, land and water shells,
and the latter class he subdivides into fluviatile and marine.

MOLLUSCA. 36

His inferior divisions are destitute of precision, and the num-
ber of species referred to limited.

The system of D'Argenville, which was so much esteem-
ed and so long followed in France, is essentially the same
with that of Lister in the higher divisions. The plan is in-
deed so simple, and in appearance so natural, that it has met
with many admirers. It has even been useful in encourag-
ing naturalists to study particular departments of the science,
when they were prevented by their situation from devoting
their attention to the whole. It is probably to this circum-
stance that we are indebted to Schroter for his observations
on the land shells in the neighbourhood of Thangelstadt,
and on the river shells of Thuringia.

The preceding arrangements, formed according to the
situations in which the animals reside, and not according to
their external coverings, may be considered as the first at-
tempts at a natural method in conchology. They serve as
an introduction to a new class of authors, whose views may
be considered as of a higher order, and to whose labours we
shall devote our attention in the following section.

SECT. III. — Systems constructed from Circumstances con-
nected with the Form and Structure of the contained Ani-
mal.

The first attempt of any consequence to arrange testace-
ous animals according to the soft parts of their bodies, was
made by Adanson, in his Histoire Naturelle du Senegal,
published at Paris in 1757. In this system, the ancient
classes of Univalves, Bivalves, and Multivalves, are em-
ployed under the titles les Limarons, les Conqucs, and les
Conques Multivalves.

36 MOLLUSC A.

CLASSE I. Les Limacons.

Sect. I. Les Lirnacons Univalves.

Fam. 1. Les limacons univalves qui n'ont ni yeux ni
cornes.

Fam. 2. Les limacons univalves qui ont deux cornes, et
les yeux places a leur racine et sur leur cote interne.

Fam. 3. Les limacons univalves qui ont quatres cornes,
dont les deux exterieurs portent les yeux sur le sommet.

Fam. 4. Les limacons univalves, qui ont deux cornes et
les yeux places a leur racine, et sur le cote externe, ou pas
derriere.

Fam. 5. Les lin^ons univalves qui ont deux cornes et
les yeux poses un peu au dessus de leur racine et sur leur
cote exteme.

Sect. II. Les Limacons Opercules.

Fam 1. Lindens opercules qui ont deux cornes, avec un
renflement, et qui portent les yeux ordinairement au dessus
de leur racine, et a leur cote externe.

Fam. 2. Lin^ons opercules qui ont deux cornes sans
renflement, et les yeux places a leur racine, et sur leur cote
externe.

Fam. 3. Limacons opercules qui ont tjuatres cornes, dont
les deux exterieurs portent les yeux sur leur sommet.
CLASSE II. Les Conques Bivalves.

Fam. 1. Les conques bivalves qui ont les deux lobes du
manteaux separes dans tout leur contour.

Fam. 2. Les conques bivalves dont les deux lobes du
manteau forment trois ouvertures sans aucun tuyau.

Fam, 3. Les conques bivalves dont les deux lobes du
manteau forment trois ouvertures, dont deux prennent la
figure d'un tuyau'assez long.

MOLLUSCA, 37

The presence or absence of an operculum or lid, gives
rise, in this system, to a division of the univalves into two
sections, and the families are established from circumstances
connected with the number of the tentacula, and the num-
ber and position of the eyes. The families amongst the
bivalves are arranged according to the structure of their
cloak or external covering. In the class of multivalves,
which we have omitted in the table, the characters are taken
from the form and structure of the shell.

The work of OeofFroy, entitled Traite Sommaire des Co-
quilles tant flumatiles que terrestres, qui se trouveni aux
environs de Paris, 1767, is constructed upon the principles
of Adanson. Here, however, the objects were not suffi-
ciently numerous to admit of all the subdivisions of that
author, but he has made the form of the animal subservient
to the construction of generic characters.

After these attempts to classify the animals which inhabit
shells had been made in France, the celebrated zoologist of
Denmark, O. F. Miiller, turned his attention to the same
subject. In the Zoologia Danica, which contains his di-
gested views of the subject, he employs, in the construction
of his genera of univalves, the characters first used by Adan-
son ; but among the bivalves, besides the form of the tubes
or syphon, he notices the construction of the branchiae and
the presence or absence of a foot.

To our knowledge of the animals which inhabit bivalves,
Poli, in his expensive work, the History of the Shells of the
Two Sicilies, made very important additions. In the con-
struction of his families, which are six in number, he em-
ploys merely the characters furnished by the syphon and
foot. In the first family, the animal has two syphons and
a foot; in the second, tfiere is only one syphon and foot;

38 MOLLUSCA.

in the third, a syphon and no feet; in the fourth there is an
abdominal syphon and no feet ; in the fifth there is a foot
but no syphon ; while, in the sixth, neither foot nor syphon
can be discovered. In the formation of his genera, Poli takes
advantage of the various forms of the cloak and the branchiae.

To the celebrated Cuvier, the conchologist is also under
the greatest obligations. By applying his vast knowledge
of anatomy to the examination of the molluscous animals, he
has unfolded many new conformations of parts, and exhi-
bited many unlooked-for relations. The vast collection of
objects, the spoils of all the museums of the continent, which
Paris once possessed, lay open to his inspection, and his in-
dustry appears to have been equal to the harvest which in-
vited him to labour.

In his first attempts to classify the molluscous animals, as
contained in his Tableau Elementaire de THistoireNaturelle
desAnimaux (1798) ; and his Lemons cFAnatomie Comparee.
(1800-1805), he employed chiefly the characters which the
preceding writers had developed, in his inferior divisions ;
but in his primary distinctions, he distributed the mollusca
into three classes : Cephalopoda, having the head covered
with tentacula, serving as feet; Gasteropoda, with the head
free, the animal "crawling on the belly; and Acephala, hav-
ing no distinct head.

Some years after the appearance of this classification,
Cuvier directed more of his attention to the internal struc-
ture of the mollusca, and, by means of accurate dissections,
obtained a more intimate acquaintance with the organs and
functions of these animals than any of his predecessors had
acquired. The information which he thus gained was com-
municated to the public at different periods, in the well-
known publication Annales du Museum d'Histoire Nafu-

MOLLUSCA. 39

relle de Paris. These papers, with some additional obser-
vations, were at last published in a separate form, under the
title Memoires pour servir a Vhistoire et a V Anatomic des
Mollusques, Paris, 1816. In the following year he published
Le Regne Animal, distribue d'apres son organisation, in
which he arranged the mollusca according to his peculiar
views, from characters drawn exclusively from the animal.
In the third volume, of what may be termed the third edi-
tion of that invaluable work, published in 1830, the same
arrangement, with the exception of a few modifications, was
adhered to.

He divides the mollusca into six classes, which he terms
Cephalopoda, Pteropoda, Gasteropoda, Acephala, Brachi-
opoda, and Cirrhipoda.

In the class CEPHALOPODA, the body is in the form of a
sack, open above, containing the branchiae, with a distinct
head, surrounded by fleshy elongations or arms, adapted for
moving the body or seizing prey. Into this class, along with
the Sepia of Linnaeus, Cuvier has inserted the multilocular
shells of his genus Nautilus and the genus Argonauta. But
it is to be feared, that our knowledge of the testaceous mol-
lusca which inhabit the numerous multilocular shells, is too
limited to enable us to assign to all of them their true place
in a natural arrangement of animals.

In the second class, termed PTEROPODA, the body is
closed, the head is destitute of the long fleshy arms which
distinguish the animals of the preceding division; two fin-
like membranes, situate on the sides of the neck, and on
which the branchial tissue is in general spread, serve as or-
gans of motion. There is only one shelly mollusca belong-
ing to this class, viz., the anomia tridentata of Forskaehl,
now forming a part of the genus Hyaloea.

40 MOLLUSCA.

The third class, which includes a great number of naked
and testaceous mollusca, and to which Cuvier gives the name
GASTEROPODA, from the circumstance of the belly being
formed for crawling, has been subdivided into eight orders,
from circumstances connected with the organs of respira-
tion.

In the first order, termed Pulmones^ which breathe air,
he has constituted two divisions, the terrestrial and the aqua-
tic. The animals of the former live on land, and were in-
cluded by Linnaeus in his genera Umax and turbo. They
are the land shells of most authors. Those of the division,
termed aquatic, live in the water, but require at intervals to
come to the surface to obtain fresh air. They constitute,
with a few exceptions, the fresh water shells of naturalists.
In the second and third orders, or Nudibrmiclies and Infero-
branches, the species consist almost entirely of genera formed
from the animals which Linnaeus and many others included
in the genus Doris. They are naked mollusca, and are like-
wise destitute of any internal testaceous plate. The fourth
order, termed Tectibranches, contains animals whose branch-
iae, like small leaves more or less divided, are situate on the
right side, or upon the back. The animals of this division
possess a shell, but it is in general placed beneath the com-
mon integuments, such as the genus Aplysia and several
species of the genus Bulla. .The fifth order, termed Heter-
opodes, have the gills plumore and dorsal, with the foot
compressed and vertical like a fin, with a small portion of
it only formed to act as an organ of adhesion, as in the other
gasteropoda. The Pectinibranches form the sixth order,
and are distinguished by the branchiae, which are like leaves
or threads placed parallel in one, two, or three lines, on the
surface of the pulmonary cavity, and by having the sexes

MOLLUSC A. 41

separate. It includes the whole of the marine species of the
Linnaean genera of turbinated univalves. Into this order,
Cuvier, from the consideration of other characters, has in-
serted the genus Cyclostoma, which, according to the cha-
racters indicated by the respiratory organs, belongs to the
Pulmones.

In the seventh order, termed Scutibranches, the bran-
chiae are similar to those of the preceding order, but the
sexes are united, each individual being capable of impreg-
nating or being impregnated. The shells in general are
cup-shaped, and destitute of a lid. It includes the genus
Halyotis, and many species of the old genus Patella. In
the last order, called Cyclobranckes, the branchiae appear in
the form of small leaves or pyramids strung round the under
margin of the cloak. They enjoy a hermaphroditism simi-
lar to those of the preceding order. The species of the
genus Patella which are allied to the vulgata, and the genus
Chiton, are included in this order.

In the fourth class, or ACEPHALA, he includes the bivalve
shells, distributing them into families, from characters near-
ly similar to those which we have pointed out as having
been previously employed by Poli.

The fifth class, termed BRACHIOPOPA, contains animals,
resembling those of the preceding class in having a cloak of
two lobes, but these are always open. The branchiae con-
sist of small leaves placed on the inner margin of each lobe.
In place of a foot they have two retractile fleshy arms,
which are extensile. This class includes the Patella unguis
of Linnaeus, the genus Terebratula and the Patella anomala
of Miiller.

The class CIRRHIPODA, distinguished by the articulated
filaments with which the animals are furnished, contains the

42 MOLLUSCA.

species of the genus Lepas of Linnaeus. The shells belong-
ing to the Linnaean genera Sarpula and Dentalium, are
transferred to the class termed Annelides.

This system of the molluscous animals is unquestionably
the most perfect of all those which have been published.
But, with all its excellence, we must inform the reader,
that many species, nay, whole genera, have their places as-
signed them in this natural method, merely because the
shells occupied a similar position in the artificial system, the
form of the inhabitants being unknown.

SECTION IV. — Mixed Systems.

In this section, we shall confine our remarks to the only
system of this kind of any consequence which has hitherto
appeared, and which is the production of the late industrious
Lamark, one of the most celebrated zoologists of the French
school. The Systems des Animaux sans Vertebres, Paris,
1801, of this author, embraces the whole range of animals in-
cluded in the classes Insecta and Vermes of Linna3iis. Where
treating of the Mollusca he divides them into two orders.
The first, termed Cephalous, from possessing a head, in-
cludes the univalves. The second, termed Acephalous, from
the absence of a head, includes the bivalves. This eminent
author greatly modified his views, as appears from what he
announced in his Extraitdu Cours de Zooloyie, Paris, 1812,
the prelude to his last and great work, Histoire Naturelle
des Animaux sans Vertebres, the fifth, sixth, and seventh vo-
lumes of which refer to the Mollusca, he fortunately lived to
finish between the years 1818 and 1 822. The arrangement
adopted in this invaluable work, has been greatly admired,
a circumstance which induces us to give the following sy-
noptical view of its contents.

MOLLUSCA. 43

The species considered by the older naturalists as shells
and mollusca, are in this system of Lamark distributed into
three great divisions or classes, which he has denominated
CntRHirEDA, CoNcniFERvE, and MOLLUSCA. These classes
he has subdivided according to the following tabular view :

CIRRIPEDES.

Animalia mollia, capite oculisque carentia, testacea, fixa.
Corpus subresupinatum, inarticulatum, tegument! appen-
dice involutum, disuper brachiis lentacularibus, cirratis,
multiarticulatis instructum.

Os subinferum, non prominulum ; maxiilis transversali-
bus dentatis per paria dispositis. Brachia numero varia, in-
equalia, biordinata ; singula cerris geminatis, setaceis, mul-
tiarticulatis, ciliatis tegumento corneo indutis, pediculo im-
positis. Anus tubum proboscedeum terminans.

Medulla longitudinalis nodosa, branchiae externae, inter-
dum absconditae ; circulatio corde vasculisque confecta.

Testa vel sessilis vel pediculo flexili tendineo elevata ;
valvis pluribus modo mobilibus, modo ferruminatis, tegu-
ment! appendice intus vestitis.

ORDRE PREMIER. — CIRRHIPEDES SESSILES.

•*• Leur corps n'a point de pedoncule, et se trouve enferme dans une
coquille fixee sur les corps marius. La bouche est a la partie su-
perieure et anterieure du corps.

1. Opercule Quadrivalve.

GEN. Tubinicelle, Coronule, Balane, Acaste.

2. Opercule bivalve.

GEN. Pyrgome, Creusie.

ORDRE SECOND. — CIRRIPHEDES PEDONCULES.
Leur corps est soutenu par un pedoncule tubuleux, mobile, dont

44 MOLLUSCA.

la base est fixe'e sur les corps marins. La bouche est presqu' in-
ferieure.

(1.) Corps incompletement enveloppe par sa tunique. Sa coquille
composee de pieces contigiies, laisse a 1'animal une issue libre,
lorsqu'elle s'ouvre.

GEN. Anatife, Pouce-pied.

(2.) Corps tout a fait enveloppe par sa tunique, mais qui offre une
overture anterieure. Sa coquille, formee de pieces separees,
n'a pas besoin de s'ouvrir poar la sortie des bras de le animal.
GEN. Cineras, Otion.

CONCHIFERES.

Animalia mollia, inarticulata, in testa bivalvi perpetuo af-
•fixa, capite occulisque nullis ; ore nudo, abscondito, parti-
bus solidis destitute; pallio amplo, corpus totumamplectante,
iobos duos laminiformes formante ; lamrnis vix liberis vel
antice coadunatis. Generatio ovo-vivipara ; copulatio nulla.

Branchiae externae, intra corpus et pallium reconditae.
Circulatio semplex ; cor uniloculare. Gangliones aliquot
rari ; nervi varii ; at chorda medullaris nodosa nulla. Tes-
ta semper bivales, animal penitus vel partim recondens,
modo libera, modo affixa ; valvis scepissime cardine vel li-
gamento marginaliunitis. Partes testaceae, accessoriae, vavis
alienee, testam interdum amplificant.

ORDRE I — CONCHIFERES DIMYAIRES.

Us ont au moins deux muscles d'attache. Leur coquille offre in-
te'rieurement deux impressions musculaires separees et laterales.
1. Coquille reguliere, le plus sou vent e'quivalve.
(a) Coquille en general b^ante aux extre'mites laterales, ses

valves ^tant rapprochees.

(*) Conchifires crassipzdes. Leur manteau a scs lobes r^unis par-de-
vant, entierement on en partie; leurpied est e'pais^ posterieur; le

MOLLUSCA. 45

baillement de leur coquille est toujours remarquable, souvent
considerable.

(1.) Coquille, soit contenuedans un fourreau tubuleux, distinct de
ses valves, soit entierement, ou en partie incrustee dans la paroi
de ce fourreau, soit saillante au-dehors.

Les Tubicolees.

(2.) Coquille sans fourreau tubuleux.
(aj Ligament exte'rieur.

(•}•) Coquille, soit munie de pieces accessoires, etrangeres a
ses valves, soit tres baillante anterieurement.

Les Pholadaires.

, (ft) Coquille sans pieces accessoires, et baillante seulement aux
extremites laterales.

Les SolJnacees.
fb) Ligament interieur.

Les Myaires.

(**) Conchiferes tenuipedes. Leur manteau n'a plus ou presque plus
ses lobes reunis par- devant ; leur pied est petit, comprime j
le baillement de leur coquille est souvent peu considerable,
(t) Ligament interieur, avec ou sans complication de ligament ex-
terne.

Les Mactrace'es, Les Corbule'es.
(+f) Ligament uniquement exterieur.

Les Lithophages, Les Nymphace'es.
(b) Coquille close aux extremites laterales, lorsque les valves son!

ferme'es.

(***) Conchiferes lamellipedes. Leur pied est applate, lamelliforme ;
non poste'rieur.

Les Conques, Les Cardiacees, Les Arcacees, Les Nayades.
(2 ) Coquille irre'guliere, toujours inequivalve.
Les Camacees.

ORERE II. — CONCHIFERES MONOMY AIRES.
Us n'ont qu'un muscle, qui semble traverser leur corps. Leur

46 MOLLUSCA.

coquille offre interieurement une impression musculaire subcentrale.

I. Section. Ligament marginal, allonge sur le bord sublineaire.

(a) Coquille transverse, equivalve, a impression musculaire allon-
gee, bordant le limbe superieur.

Les Tridacnees.

(b) Coquille, soit longitudinale, soit subtransverse, a impression
musculaire resserree dans un espace isole sans border le limbe.

(t) Ligament au bord lateral de la coquille et toujotirs entier.

Les Mytilaces.

(ft) Ligament au bord inferieur de la coquille, ou divise.
Les Malleacecs.

II. Section. Ligament non marginal, resserre dans un court espace

sous les crochets, toujours connu, et ne formant point un tube
tendineux sous la coquille.

(a) Ligament interieur ou demi interieur. Coquille re'gulaire, a
test compact non feuillete.

Les Pectinides.

(b) Ligament interieur ou demi interieur. Coquille irreguliere, a
test feuillete, quelquefois papyrace'.

Les Ostraciees.

III. Section Ligament, soit nul ou inconnu, soit represente par

un cordon tendineux qui soutient la coquille.

(a) Ligament et animal inconnus. Coquille tres-inequivalve.

Les Rudistes.

(b) Coquille adherente, soit Jmmediatement, soit par un cordon

tendineux qui la soutient et lui sert de ligament ; 1'animal ayant
deux bras opposes, cilies et cirreux.

Les Brachiopodes.

MOLLUSQUES.

Animalia mollia, inarticulata, antice capitata ; capite plus
minusveprominulo,oculis tentaculisque scepissime instructo,

MOLLUSCA. 47

aut brachiis pluribus superne coronato. Os, vel breve, vel
elongatum, tubulosum, exsertile, soepius partibus duris ar-
matum. Pallium varium ; modo marginibus liberis ad cor-
poris latera, modo lobis in saccum coadunatis corpus par-
tim vaginans.

Branchiae variae, raro symmetricae ; circulatio duplex, par-
ticularis et generalis. Cor uniloculare ; interdum auriculis
duabus divisis et valde remotis. Chorda medullaris nodosa
nulla ; at gangliones sparsi rariusculi, nervique varii.

Corpus modo externe nudum, et intus vel partibus soli-
dis destitutum, vel testam aut corpora aliquot dura recon-
dens ; modo extus testa vaginante vel obumbrante tectum.
Testa nunquam valvis duabus oppositis et cardine margin-
ali unitis composita.

I. ORDRE. — LES PTEROPODES.

Point-de pied pour ramper, ni de bras pour se trainer ou saisir le
proie. Deux nageoires opposees et semblables, propres a la nata-
tion. Corps libre, flottant.

1. Hyale; 2. Clio; 3. Cleodore ; 4-. Limacine ; 5. Cym-
bulie ; 6, Pneumodernie.

II. ORDRE. — LES GASTEROPODES.

Animaux a corps droit, jamais en spirale ni enveloppe dans une
coquille qui puisse le contenir en entier ; ayant sous le ventre un pied
ou disque musculeux uni au corps a peu pres dans toute sa longueur,
et servant a ramper.

Les uns nus, d'autres ombrages par une coquille dorsale, non en-
gainante, et d'autres encore contenant une coquille plus ou moins
cachee dans leur manteau.

I. Section — Branchies, quelle qui soit leur possition, s'elerant, soit
en fillets, soit en lames, soit en piegnes ou panaches. Elles ne
respirent que 1'eau.
(Hydrobranches.)

48 MOLL.USCA

(a) Branchies exterieures, placees au-dessus du manteau, soit sur

le dos, soit sur ces cote-i, et n'etant point dans une cavite par-
ticuliere.

Les Tritoniens.

(b) Branchies exterieures, placees sous le rebord du manteau, et
disposees en serie longitudinale, soit autour du corps, soit d'un
seul cote ; n'etant. pas non plus dans une cavite particuliere.

Les Phyllidieris, Les semi-Phyllidiens.

fcj Branchies placees dans une cavite particuliere sur le dos situee
anterieurement pres du cou.

Les Calyptracions.

(d) Branchies placees dans une cavite particuliere, vers la partie
posterieure du dos, et recouvertes, soit par le manteau, soit
par un ecusson operculaire.

t Point de tentacles.

Les Bul'ens.
•H Des tentacules.

Les Laplysiens.

II. Section. ' Branchies rampantes, sous la forme d'un reseau vascu-
Jeux, sur la paroi d'une cavite particuliere dont 1'ouverture est
un trou que 1'ammal contracte on dilate a son gre. Elles ne
respirent que Tair libre.
( Pneumobranches. )

Les Limaciens.

III. ORDRE — LES TRACHELIPODES.

Le corps contourne en spirale dans sa partie posterieure, cette par-
tie etant separee du pied, et toujours enveloppee dans une coquille.
Le pied libre, aplati, attache a la base inferieure du cou, ou a la par-
tie anterieure du corps, et servant a ramper. Coquille spirivalve en-
gainante.

I. Section. Trachelipodes sans siphon saillant, et respirant en ge-
neral par un trou. La plupart phytiphages et munis de machoi-

MOLLTJSCA. 49

res. Coquille a ouverture entiere, n'ayant a sa base ni echan-
crure dorsale subascendante ni canal.
* Trachelipodes ne respirant que 1'air. Coquille spirivalve, mutique

non distinctement nacree.
(a) Ceux qui habitent hors des eaux.

Les Colimaces,

(b) Ceux qui vivent dans les eaux, mais qui viennent respirer 1'air
3. leur surface. Coquille a bords de 1'ouverture jamais reflechis.

Les Lymneens.

** Trachelipodes ne respirant que 1'eau. Branchies saillantes en-
forme de filets, de lames ou de hupes, dans la cavite branchi-
ale. Coquille souvent nacree et souvent aussi ayant des par-
ties protuberantes a sa surface.

(a) Coquille fluviatile, operculee, dont le bord gauche n'imite pas
une demi-cloison.

(f) Coquille a bords desunis.

Les Melaniens.
(ft) Coquille a bords reunis.

Les Peristomiens.

fbj Coquille fluviatile ou marine dont le bord gauche imite une
demi-cloison.

Les Neritaces.

c. Coquille marine, dont le bord gauche n'imite pas une demi-
cloison.

(t) Coquille flottante a la surface des eaux.

Les Janthines,

(ft) Coquille non flottante, ayant 1'ouverture tres evasee ; point de
columelle.

Les Macrostomes.

(ttt) Ouverture sans evasement particulier j des plis a la colu-
melle.

D

M MOLLUSC A.

Les Plicaccs.

(tttt) Point de plis a la columelle.

fa) Les bords de 1'ouverture reunis circulairement.

Les Scalariens.
(h) Les bords de 1'ouverture desunis.

Les Turbinaccs.

II. Section. Trachelipodes a siphon saillant, et ne respirant que
1'eau qui parvient aux branchies par se siphon. Tous sont
marins zoophages, despourvus de machoires et munis d'une
trompe retractile. Coquille spirivalve, engainante, a ouverture,
soit canaliculee, soit echancree ou versante a sa base.
fa) Coquille ayant un canal plus ou moins long a la base de son

ouverture, et dont le bord droit ne change point de forme avec Page.

Les Canaliferes.

Cb) Coquille ayant un canal plus ou moins long a la base de son
ouverture, et dont le bord droit change de forme avec I'age et a un
sinus inferieurement.

Les Ailees.

(c) Coquille ayant un canal court, ascendant posterieurement, ou
une echancrure oblique en demi-canal a la base de son ouverture, ce
demi-canal se dirigeant vers le dos.

Les Purpuriferes.

(d) Point de canal a la base de 1'ouverture, mais une echancrure
subdorsale et des plis, sur la columelle.

Les Columellaires.

fej Coquille sans canal, mais ayant la base de son ouverture echan-
cree ou versante,*et ses tours de spire etant larges, comprimes, en-
roules de maniere que le dernier recouvre presque entierement les
autres.

Les EnrouL'es.

IV. ORDRE. — LES CEPHALOPODF.S.
Manteau enforme de sac, contenant la partie inferieure du corps.

MOLLUSCA. 5 1

Tete saillante hors du sac, couronnee par des bras non articules, gar-
nis de ventouses, et qui environnent la bouche. Deux yeux sessiles ;
deux mandibules cornees a la bouche ; trois cceurs ; les sexes separes.

I. DIVISION CEPHALOPODES POLYTHALAMES.

Us ont une coquille multiloculaire, partiellement ou completement
interietire, et enchassee dans la partie posterieure de leur corps.
* Coquille multiloculaire a cloisons simples.

Leurs cloisons ont les bords simples et n'oflfrent point de sutures
decoupees et sinueuses sur la paroi interne du test.

(1.) Coquille droite ou presque droite : point de spirale.

Les Orthocerces.

GEN. Belemnite, Orthocere, Nodosaire, Hippurite, Conilite.
(2.) Coquille partiellement en spirale ; le dernier tour se continu-
ant en ligne droit.

Les Lituolees.

GEN. Spirale, Spiroline, Lituole.
(3.) Coquille semi-disco'ide, a spire excentrique.

Les Cristacces.

GEN. Renuline, Cristellaire, Orbiculine.

(4.) Coquille globuleuse, sphero'ides ou ovale ; a tours de spire
enveloppans ou a loges reunies en tunique.

Les Spherulees.

GEN. Miliole, Gyrogone, Melonie.

(5.) Coquille disco'ide, a spire centrale, et a loges rayonnantes du
centre a la circonference.

Les Radiolaes.

GEN. Rotalie, Lenticuline, Placentule.

(6.) Coquille discoide, a spire central, et a loges qui ne s'etendent
pas du centre jusqu'a la circonference.

Les Nautilaces.
GEN. Discorbe, Siderolite, Polystomelle, Vorticiale, Num-

inulite, Nautile.
** Coquille multiloculaire, a cloisons decoupees sur les bords.

52 MOLLUSCA.

Les Ammon'es.

GEN. Ammonite, Orbulite, Ammonocerate, Turrilite, Ba-
culite.

2. DIVISION. — CEPHALOPODES MONOTHALAMES.

Coquille uniloculaire, tout-a-fait exterieure, et enveloppant 1'animal.
GEN. Argonaute.

3. DIVISION. CEPHALOPODES SEPIAIRES.

Point de coquille, soit interieure, soit exterieure. Un corps solide,
libre, cretace ou come, contenu dans 1'interieur de la plupart de ces
animaux.

GEN. Poulpe, Calmaret, Calmer, Seche.

V. ORDRE. — LES HETEROPEDES.

Corps libre, allonge, nageant horizontalement. Tete distincte ;
deux yeux. Point de bras en couronne sur la tete ; point de pied
sous le ventre ou sous la gorge pour ramper. Une ou plusieurs na-
geoires, sans ordre regulier et non disposees par paires.
GEN. Carinaire, Firole, Phylliroe.

The authors of the first class of conchologists which we
have mentioned, employ exclusively the characters furnish-
ed by the shell, and scarcely deign to tell us that there is
an animal attached to that shell. The authors of our third
class are anxious to keep the shell out of view, and draw
their distinctions from the animal ; but they have -failed in
the attempt. In extreme eases, the characters of the shell
are resorted to in the absence of distinctions furnished by
the animal.

Lamark perceived the inconvenience of separating these
two modes of examining molluscous animals, and fortunate-
ly formed a very natural combination. We shall give his
character of the genus Patella, as a specimen of this mixed
system-

MOLLUSCA. 53

Patella.

Corpus testa univalvi penitus obtectum ; capite tentacu-
lis duobus acutis, basi externa oculferis. Branchiae infra
veli marginem per totam corporis periphaeriam seriatim dis-
positae. Orificia pro generatione et ano ad latus dextrum
anticum.

Testa univalvis, non spiralis, animal obumbrans, clypi-
ata vel retuso conica, imperforata ; fissura marginali destitu-
ta ; cavitate simplici ; apice anterius recurvo.

In this manner the generic character is dependent equally
on the shell and the contained animal, and that genus in a
system is consequently not sufficiently established in which
both these characters are not included. How many genera
are in this imperfect state ! Were the same plan followed
in the description of species, everything we could wish for
would be detailed ; and our knowledge of the forms of mol-
luscous bodies would approach to perfection. How much is
it to be wished that this plan of Lamark's were generally
adopted in this country ! conchology would assume a new
aspect, and the number of his votaries would rapidly increase.

The reader will have perceived, in the course of the
hasty review of those systems which we have enumerated,
that we have refrained from making any remarks on their
comparative excellence. This deficiency we now propose
to supply in the following observations.

The authors who have arranged testaceous bodies, with-
out reference to the animals that reside in them, appear to
have mistaken the house for the inhabitant, and the thing
formed for the being that produced it. They have torn
asunder objects which are closely related, and united others
which differ in structure and economy. These are neces-

54 MOLLUSCA.

sary consequences of an artificial system, and they become
more obvious in proportion as we descend in the scale of
being.

The examination of shells, according to this method, may
be viewed as the study of the osteology of the mollusca. It
has not for its object the investigation of living matter, but
of dry bones. Nor has it any of those advantages which
result from the study of the osteology of the vertebral ani-
mals. A knowledge of the bones of these animals enables
us to ascertain many of their primary functions, the nature
and extent of their powers of motion, and even the food on
which they subsist. But our knowledge of shells does not
enable us to say, whether the animal can crawl or swim;
whether it feeds on plants or animals. The reason is obvi-
ous. All the muscles inserted upon the shell are either
mere organs of adhesion, or destined to open and shut the
valves. None of those muscles connected with any of the
primary organs have any connection with the shell. That
the shell furnishes several most important characters, we
readily grant ; but we are here reasoning against the pro-
priety of attending to the shell, to the exclusion of the animal,
and, to this extent, our reasoning appears to be conclusive.

We are aware, that, in the other departments of natural
history, the appearances which the external parts of an ani-
mal exhibit are constantly employed in the construction of
orders and genera, and all the intermediate divisions. Thus,
for example, the bill, feet, and feathers of birds, furnish the
characters by which they are arranged in the system. Here,
however, it must be observed, that the combined informa-
tion yielded by these parts, makes us acquainted with the
habits and organization of a bird. By means of these we
can judge, and with certainty, not merely of its internal

MOLLUSCA. 55

structure, but the places which it frequents, and the food
which it consumes. Hence these characters may be appli-
ed with equal propriety in an artificial as in a natural me-
thod. But what opinion would we form of that ornitholo-
gist, who could readily inform us that the cormorant has
fourteen tail feathers, and the shag only twelve, but who
was ignorant of the haunts of these birds, their food, and the
number of their young* We might prize him as a com-
panion in surveying a museum, but he is alike a stranger to
science and nature.

Nor can we feel more respect for the student of mere
shells. He may be able to tell us the number of whorls in
a spiral univalve, or the form of the hinge in a bivalve ; but
if he knows not the nature of the organs of respiration, di-
gestion, and reproduction of the animal to which the shell
belongs, and contentedly remains in tin's ignorance, he has
yet to learn the value of method in natural history. He
cherishes with mistaken fondness the maxim of Linnaeus,
" Nomina nosse oportet qui rem scire velit," while he over-
looks a more important object, expressed in the motto of
the Linnsean Society, " Natures discere mores."

These remarks apply to the conchological labours of Lin-
naeus and his followers, who have devoted their whole at-
tention to the arrangements of the shells, without attending
to the animals. We know that some of the admirers of
the Swedish naturalist presume to say, " But our great au-
thor was not wholly inattentive to the creatures for which
the beautiful and endless diversified receptacles that he had
characterised were designed. Among the generic marks
was included the name of the molluscous inhabitant ; or,
where the animal differed from any which had a place in
other parts of his system, he described it at length." (Linn,

00 MOLLUSCA.

Trans, vol. vii. 175.) Now, to what does all this attention
of Linnaeus amount ? In all the species which he has de-
scribed, he has only noticed the animals of four of these,
and in a very slight manner ; and, with regard to the name
of the molluscous inhabitant which he included in his ge-
neric marks, we hesitate not to say, that by this union he
has betrayed carelessness. To many British ears these terms
may sound harsh, but the proof of their correct application
in the present instance will be abundantly evident, if we
examine the references to the animals of a few of his ge-
nera. The genus chiton is thus characterised ; " Animal
Doris. Testae plures, longitudinaliter gestae, dorso incum-
bentes." Are we not led to conclude from this character,
that the animals of the chiton exactly resemble the animals
of the doris genus, with the addition of the shells ? If this
be the case, how artificial is that system which places these
two genera in separate orders ! Upon turning, however,
to the genus doris among his vermes mollusca, we find the
following characters assigned to it ; " Corpus repens, ob-
longum, subtus planum. Os antice subtus. Anus postice,
supra cinctus ciliis. Tentacula duo, supra corpus antice
intra foramina retractilia." Now, the fine fringes around
the anus of the doris, which are the branchiae of the animal,
and form the essential character of the genus, are not to be
found in the animals of the chiton, whose branchiae are in
the form of leaves placed along the margin of the body, and
the anus is a simple pore.

According to the generic character of the mya, the ani-
mal is an ascidia, with the appendage of a shell. Upon
turning to the genus ascidia, we find it said, " Corpus fix-
urn, teretiusculum, vaginans. Aperturae binae, ad summi-
tatem ; altera humiliore." To prove the impropriety of re-

MOLLUSCA. 57

ferring the animal of the mya to the genus ascidia, we shall
only mention, that the former has a foot, and possesses a
locomotive power ; the latter has no foot, remains immove-
ably attached for life upon the substance to which it at first
adhered, and depends on the accidental bounty of the waves
for all its nourishment.

The animals of nearly all the univalves are represented
as belonging to the genus Umax. But, with the exception
of the restricted genus helix and bulimus, the animals of the
univalves are all genetically different from the Umax. Their
tentacula are generally two in number, with the eyes at the
base ; while the tentacula are four in the Umax, with the
eyes at the tips of the two longest. These examples will
suffice to establish a truth so palpably obvious.

The principal objection against this system of employing
the shell, to the exclusion of the animal, arises from the
fact, that nature has not drawn a line of distinction between
the mollusca and the testacea. Thus, many of the vermes
mollusca of Linnaeus include shells in their bodies, as the
aplysia ; and many of his vermes testacea likewise are soft
on the outside, the shell being inclosed by the integuments,
as the helix laevigata, now constituting the genus VELUTJNA.

We have another objection to this artificial system, and
one which we consider of great force ; that, wherever it
prevails, the form and habits of the animal are overlooked.
How fully is this truth illustrated in the works of the testa-
ceologists of this country ! We might examine all their
writings, from the Pinax of Merret to the Descriptive Ca-
talogue of Maton and Raket, including the works of Pen-
nant, Berkenhout, Da Costa, and Donovan, and learn little
more, besides the habitat, than that to every shell there is
an animal attached. Of this charge the names of Lister

58 MOLLUSCA.

and Montag.i stand acquitted. The former has given us
several good dissections, and the latter minute descriptions
of the testaceous animals.

Whilst, in the preceding remarks, we have objected to all
arrangements taken exclusively from the characters of the
shell, we also disapprove of those systems founded exclu-
sively on the characters of the animal. By the former class
of methodists, the simplicity of nature is sacrificed to their
peculiar views, and, by the latter, practical utility is disre-
garded. Devoting their whole attention to the animal, the
later naturalists have overlooked the house in which it
resides ; the roof which shelters it from the blast ; and the
walls which guard it from its foes. The former observ-
ers possessed very limited views of nature, and erected
systems obviously artificial. To the systems of the latter,
the same objections will apply. Thus, for example, among
the univalves of Adanson, the families are formed from the
position of the eyes chiefly. That the black points which
we witness at the tips or at the base of the tentacula are
actually eyes, we readily admit ; but what influence have
these eyes on the habits of the animal ? or rather, does a
change of position of these organs occasion a corresponding
change in the habits of the animal ? Unless this is answered in
the affirmative, we must consider such characters as equally
artificial with any employed by Linnaeus or his followers,
since they have no relation to any of the primary functions
of life.

The employment of characters taken exclusively from the
anrmal is attended with so many practical difficulties, that
it never can be introduced into general practice. If we find
a shell thrown ashore, the animal may be dead, or it may re-
fuse for a time to display its organs, and prevent us from

MOLLUSCA. 59

arriving at its name and history. This defect, however,
is partly remedied when we can call to our aid the charac-
ters furnished by the shell.

Another objection against this method arises from the well
known difficulties attending the preservation of the soft parts
of molluscous animals. To dry these, destroys their form and
texture ; to inject them is impracticable ; and when put
into spirits of wine, they generally appear a shrivelled mass.
But the coverings of these animals are durable, and, since
they form a part of the animal ; since they are produced at
first along with it, increase by the addition of new matter
from its body, and continue attached to it for life ; we must
condemn any classification from which the shell is excluded*

From these remarks, it will be obvious, that we consider
the mixed system as the most natural and the most useful.
It possesses all the advantages to which the other systems
lay claim, while it is free from their defects. It withdraws
part of our attention from the shell, because it is destitute
of peculiar vessels, and possesses no vital energy, to fix it
on those organs of the animal which are subservient to its
existence. It leads us to examine the whole animal, instead
of certain parts of it merely, and has a tendency to excite
us to become acquainted with the manners of a tribe, from
which, imperfect and artificial systems have hitherto with-
drawn our attention.

VALUE OF THE CHARACTERS EMPLOYED.

It is of the utmost importance in the formation of any ar-
rangement of natural bodies, to have an exact idea of the
relative value of the characters used, and of their true sub-
ordination. This is a subject of vast moment, and too little

60 MOLLUSCA.

attended to by naturalists. We do not here consider that
character as of the highest kind, which is the most general,
but that which has the greatest influence over the faculties
and instincts of the animal. Had this subject been studied
with greater care, the science of conchology would, at this
period, have been in a more flourishing condition. To as-
certain, in some degree, this subordination of character, is
the object of the following observations.

The division of the testaceous mollusca into three orders,
as adopted by Linnaeus, is confessedly artificial. The Mul-
tivalvia of that author possess no characters in common, nei-
ther can they boast of a general resemblance. The first
genus, Chiton, consists of animals which belong to the ce-
phalous and gasteropodous mollusca. The animals of the
genus Lepas approach more nearly to the Crustacea than
the mollusca ; while the animals, inhabiting the genus Pho-
las, belong to the acephalous mollusca, and are closely con-
nected with the Myae and Solenes. The shells of the first
genus are merely calcareous scales, arranged transversely on
the back of the animal. The shells of the second genus
are variously articulated, fixed, and either sessile or pedun-
culated. The shells of the third genus are bivalves, with a
few accessory calcareous plates. It is to be hoped that mo-
dern conchologists will avoid so incongruous a combination.

The two remaining divisions of Linnaeus, the bivalves
and univalves, are not only obvious, but natural. They in-
dicate the existence of certain forms peculiar to the animals
whose shells are thus separated in the system. The uni-
valve shells are inhabited by animals which possess a head,
and whose organs of motion are either tentacula situated on
the head, or a foot spread over the belly, as in the slug.
The animals of the bivalve shells, on the other hand, are

MOLLUSCA. 61

destitute of a head ; some of them have no locomotive
power ; and, in others, the organ of motion is a fleshy foot,
which the animal can protrude at pleasure. These circum-
stances point out the connection which subsists between
the organs of the animal, and the external forms of the shell;
a connection which, in every system, ought to be carefully
attended to.

It is somewhat difficult to point out, among the univalves,
the true subordination, or relative importance of the cha-
racters employed by conchologists in describing them. We
have much to learn of their anatomy, and hence we cannot
with certainty point out the relation of the parts of the shells
to the organs which those parts protect. The form and struc-
ture of the mouth of the shell, however, may be expected to fur-
nish characters of the first-rate importance, and have always
attracted the notice of the student of testaceous bodies. The
very shape of the animal, together with its ordinary habits,
must necessarily depend, in a great measure, on the form of
the mouth.

In many genera, the mouth of the shell towards the base
is produced, and terminates in a groove or beak. These
univalves are termed canaliculated, and are readily distin-
guished from those whose mouth is entire. The differences
in the form of the shell in these two divisions is an index of
equally remarkable differences in the form of the animals.
The canaliculated shells contain animals possessed of an
elongated tube for the purposes of respiration, and this canal
is destined for its reception and protection when expanded.
The animals whose shells are destitute of this canal, are
likewise destitute of this lengthened respiratory tube. Cir-
cumstances of this kind induce us to believe, that shells,
agreeing in external form, in general, contain animals of a

62 MOLLUSCA

similar organization. We consider this division of the uni-
valves into canaliculated and entire, as obvious and natural.

The next character, in point of importance, appears to
depend on the direction of the revolutions of the spire. In
general, when a spiral univalve is placed upon its base, or
mouth, with its summit towards the observer, the mouth
will open on the right side of its axis or pillar, and the
whorls will be observed to revolve from right to left, be-
ginning at the base, and ending at the summit. These
shells are termed dextral. In a few shells, however, this
order is reversed. The mouth^occurs on the left side of the
pillar in the above-mentioned position, and the whorls from
the mouth to the summit revolve from left to right. Shells
of this sort are termed sinistral, sometimes also heterostro-
phe or heteroclite, and are generally called by dealers unique.

In the dextral shells, the animals have the external open-
ings of the rectum, penis, and uterus, on the right side of
the body, and the heart on the left. In the sinistral shells,
these organs are placed on the opposite sides. Thus the
openings of the rectum and organs of generation are on the
left side, while the heart is situated on the right. Here
again we have an external character impressed on the shell,
which indicates certain arrangements in the organs of the
animals. We are aware that some conchologists consider
the sinistral shells as accidental varieties, and on that ac-
count regard the character which is indicated as of inferior
importance. Bosc, indeed, says, " La cause de cette varia-
tion dans la direction des spires, vient des circonstances
dans lequelles s'est trouve 1'animal au moment de sa nais-
sance, et d'un obstacle qu'il a trouve lorsqu'il a voulu tour-
ner sa tete du cote que la nature lui a indique." This ex-
planation might have been received, had such changes in

MOLLUSCA. 63

the direction of the whorls been confined to one individual
or two, of particular species. But when we observe all the
individuals of particular species, nay even of genera with
their whorls thus invariably reversed, we are disposed to re-
gard the occurrence as connected with the primary struc-
ture of the animal, and not as the result of accident. Be-
sides, the viscera of the animal of a reversed shell are not
placed in the same position in relation to its back or belly,
as the animals of the dextral species. A simple change of
direction in the spire, therefore, will not convert a dextral
into a sinistral species, and the character must be consider-
ed as of a higher order than those employed for the separa-
tion of the species merely. We consider sinistral shells as
belonging to distinct genera from those which are dextral,
it being inexpedient to make use of the character for higher
divisions.

Among many of the univalves, the animal is furnished
with a lid, by means of which it can close up the entrance
of the shell after it has withdrawn itself into the cavity. It
is in general corneous, sometimes also calcareous. It is
usually flat, and attached to the superior and posterior part
of the foot of the animal. The shells which possess this lid
are generally termed operculated shells. They must not
be confounded with those land shells of which the animals
form a temporary covering to the mouth, previous to winter,
for the purpose of protecting them from the vicissitudes of
the weather. This lid, in the former case, is permanent, in
the latter deciduous ; in the former it adheres to the ani-
mal, being in connection with it ; in the latter only to the
margins of the mouth of the shell.

This character was first employed by Adanson in the con-
struction of the second section of his class univalves, and

64 MOLLUSCA.

has been more or less attended to by succeeding concholo-
gists. It is certainly a very general character, and at first
sight might be supposed worthy of forming some of the
higher divisions. It appears but rarely in the land shells,
more frequently in fresh water shells, and generally in the
marine species. It does not, as yet, appear to be connect-
ed with any peculiar organization, although it must influ-
ence to a certain extent the economy of the animal. Were
we, however, to employ it in higher divisions than generic
ones, some confusion would certainly arise. It would cause
the separation of many genera which are nearly allied, and
even divide several natural families. Thus, for example,
among the porcellaneous shells, it would separate the olives
from cones, the former being destitute of an operculum,
while the latter possess one. These two genera, however,
belong to a natural family, the animals of both genera hav-
ing a respiratory tube upon the head, and the eyes placed
on the sides of the tentacula, instead of being situated, as
in the other gasteropoda, on the tips or at the base. This
circumstance is calculated to convince us of the necessity
of caution in the admission of characters. These may at
first appear to be of extensive occurrence, and well adapted
for the formation of families, but unless they exercise some
visible influence on the animal, they can never be employ-
ed with propriety in a natural system, however convenient
they may be in an artificial arrangement. Operculated
shells may be considered as generically different from those
which are destitute of that organ, without any injury to the
natural method. It would even, in many instances, be con-
venient.

Amongst univalve shells, considerable differences are ob-
servable in the shape and position of the cavity of the shell.

MOLLUSCA. 65

In some cases this cavity is simply conical, while in others
it is conico-tubular, either revolving horizontally round a
centre, or spirally twisted upon an axis or pillar. These
circumstances furnish characters of great importance in an
artificial system, as by means of them all testaceous bodies
may be arranged into two tribes, the one possessing a pillar,
round which the tube of the shell is twisted, while the other
is destitute of any pillar. The former have been termed
Sfulidia, the latter Astulidia. As a natural character,
however, these distinctions are of inferior importance, and,
if employed would occasion a separation between the genera
Planorbis and Lymnaea, which are demonstrated by Cuvier
to be nearly related. In the formation of genera, it may
be employed with advantage, even in a natural system, aided
by the structure of the pillar, and the direction of the whorl.
The last character which we have to notice while speak-
ing of the univalves, depends on the circumstance of the
cavity being entire, or divided into chambers, being unilo-
cular or multilocular. In the multilocular testacea there
are a number of transverse plates, in some species perfor-
ated, in others entire, which cross the cavity of the shell,
and, in general, divide the external cavity, in which the
animal resides, from the older and smaller ones, from which
it has receded. In an artificial arrangement, such distinc-
tions may. be employed with advantage, even in the forma-
tion of the primary divisions, but we entertain doubts as to
the propriety of using them in a strictly natural method.
We are in a great measure ignorant of the animals which
inhabit the multilocular shells, yet as far as our knowledge
goes, we are induced to regard the distinction as merely
conventional, and as unconnected with any peculiar order
of organization. Such a division may be useful in the pre-

66 MOLLUSCA.

sent state of the science, and may be permitted on that ac-
count; but in proportion as our knowledge of the mollusca
advances, this distinction will be deemed inexpedient. In.
deed, were this division adopted, the genera Argonauta and
Nautilus would be torn from each other, although they are,
by Cuvier and many others, regarded as members of a fam-
ily of cephalopodous mollusca. The Nautilus lacustris of
Lightfoot, now constituting the genus SEGMENTINA, would,
in that case, likewise be separated from the genus Planor-
bis, with which it is very closely allied. In the meantime,
until our knowledge of the multilocular testacea arrives at
a greater degree of perfection, such divisions may be em-
ployed as convenient, and of easy application.

The preceding remarks apply to those shells which belong
to the cephalous mollusca. Among the bivalve shells,
which belong to the acephalous mollusca, the characters
which they exhibit are of very different degrees of import-
ance. Here, as among the univalves, the appearance of the
shell enables us to form an idea of the organization of the
animal, so that the characters thus furnished by the shell
may be safely employed in a natural system.

The bivalve shells, in general, possess the faculty of mov-
ing from one place to another, or of attaching themselves
to rocks and stones, by means of temporary threads. These
are termed free shells. But there are others which secrete
at their birth a calcareous cement, which unites the shell
to the rock or stone immoveably for life. These last are
known by the name ofjixed shells. If we thus consider
the difference in the economy of these two divisions of bi-
valves, we may reasonably expect to find corresponding dif-
ferences in their organization. The free shells contain ani-
mals endowed with locomotion, and by consequence with

MOLLUSCA. 67

feet. In few of the- animals which inhabit fixed shells can
a foot be observed. They are more simple in their orga-
nization than the free shells, and are destitute of absorbing or
ejecting syphons, the place of these being supplied by holes
in the duplicature of the cloak. This last distinction, how-
ever, is not peculiar to the fixed shells, although found in
all of them.

Among the free shells, a very important circumstance
occurs, which we have already noticed, viz. that some of
these adhere to rocks and stones by means of temporary
threads produced by the animal. They are termed byssi-
ferce. Independent of the utility of this power of produc-
ing threads of attachment, to the economy of the animals,
the byssiferae must possess at least three organs of which
the other testaceous mollusca are destitute. The first of
these is a gland for the secretion of the substance of which
the threads are formed ; the second, a foot so constructed
as to be capable of spinning these threads and fixing them
to the rocks or other bodies to which they are intended to
adhere ; and the third is a muscle in the animal to which
the inner end of these threads may be attached, and which
muscle, in general, has the power of contraction and elon-
gation. This character, then, appears perhaps of the very
highest order, so that, in a natural arrangement, we might
divide the molluscous bivalves into such as spin threads of
attachment, and such as do not. We must, however, con-
fess, that the byssiferae have scarcely any other subordinate
characters in common, to warrant such an arrangement.

In general, the valves of which the shell consists close
upon each other in such a manner as to leave no opening.
In a few genera, however, the valves do not close upon
each other at one end, and sometimes at both ; the point

68

MOLLUSCA.

of union being at one side or in the middle. The former
are termed close shells, the latter gaping shells. The cha-
racter of gaping, so very obvious in the shell, is an index
of equally important distinctions which prevail in the ani-
mal. In the gapers, the syphons, or the absorbing and
ejecting pipes, are two in number, and very long, and fre-
quently united. The foot is contained in a sheath, from
which it issues at the pleasure of the animal. Besides, the
branchiae are always united, and equal in length to the tubes.
This character appears, therefore, equally important as the
former. It has hitherto been employed in the construction
of specific characters merely, rarely of genera.

When the two valves are of the same size and form, the
shell is said to be equivalve ; but when the one valve differs
from the other in these particulars, the shell is said to be
inequivalve. This character, so obvious and so commodi-
ous, is not the index of any peculiar organization of the ani-
mal. If employed in the higher divisions, it would separ-
ate closely connected genera, and destroy some natural
alliances. The inequivalves, however, are for the most
part irregular in their growth. The molluscous inhabitants
have no lengthened syphon nor foot.

When we examine the inner surface of bivalves, we ob-
serve some spots of a different colour and lustre from the
general surface. These are the places to which the muscles
adhered, which connected the animal with the shell, and are
termed muscular impressions. They are either separate
and lateral, subcentral, or simple, or composite. This cha-
racter was long employed by conchologists in their specific
distinctions, and sometimes in the formation of the genera.
It has been more recently employed by Lamark, as a character
of the first importance in the division of the bivalves. He

MOLLUSCA. O9

forms these shells into two sections, the first containing
those shells which have the muscular impressions separate
and lateral, and the second such as have only one subcen-
tral, simple, or compound impression. However highly we
respect the conchological labours of this naturalist, we can-
not join with him in the present instance, and elevate a sub-
ordinate character to a primary rank. If, by muscular im-
pressions, he means those marks impressed on the valves of
the shells by the muscles which serve to close it, then his
character is unconnected with any of the primary functions
of the inhabitant. For is it of much consequence whether
the valves be brought into contact by the action of one
muscle or by the assistance of two ? In so far, the charac-
ter is evidently artificial, when the impressions of the ab-
ductor muscles only are employed. But he evidently uses
the term in a more extensive sense, to refer to those im-
pressions left on the shell by some of the other muscles by
which the animal is attached to it. To the mere concho-
logist, these marks are of a very uncertain import, and
can never enable him to construct natural families, and the
student of the mollusca will employ more important distinc-
tions. If we are to take all the muscular impressions into
account, the arrangement of Lamark must undergo great
alterations. Let us take the common mussel as an exam-
ple. It is placed by the French Conchologist in the second
section, as having only one muscular impression, although
no less than four muscles adhere to each valve, destined for
the performance of very different functions. The largest
impression, which is situate near the obtuse end of the
shell and towards the posterior margin, belongs to the ab-
ductor muscle, employed in closing the valves. Connected

70 MOLLUSC A.

with this impression there is a tongue-shaped mark, reach-
ing nearly to the ligament. This mark is occasioned by
one of the lateral muscles for supporting the byssus, and by
one of the lateral muscles of the foot. The other muscle
for supporting the byssus, is inserted under the teeth which
occur at the beak. There is even another mark of adhe-
sion on the margin of the shell, irregularly denticulated,
occasioned by the fringed margin of the cloak, which is
there united with the shell. This mark may be termed the
marginal impression. To which of these marks then are
we to attach the greatest importance ? To the impression
of the one abductor muscle, which is common to all shells,
— .to the marks of the muscle of the byssus, or to the in-
dented mark of the fringed margin of the cloak. If we at-
tend farther to Lamark's arrangement, we shall find the
Camacea separated from the Ostreacea, although the two
families possess numerous external and internal points of
resemblance. We regard the muscular impressions as fur-
nishing a convenient character for the construction of genera,
and the discrimination of species, but it is not worthy to
occupy so high a rank as Lamark has assigned to it.

As intimately connected with the muscular impressions,
we may here notice the ligament. It is a horny elastic
membrane, which serves to open the valves, when the ad-
ductor muscle relaxes. It is placed on the exterior margin
in some shells, and is concealed in others. When external,
it is stretched when the shell is closed, and when it is inter-
nal, it is compressed in similar circumstances. This cha-
racter is very useful in the construction of genera, but it
ought never to be employed in any of the higher divisions.
It is not the index of any peculiar organization, neither does

MOLLUSC A. 71

it serve to unite natural families. Lamark, without due con-
sideration, regarded it as next in importance to the muscular
impressions.

The teeth of the hinge of bivalves, since the days of Lan-
gius, have been studied with care, and the characters which
they furnish have been employed, both in artificial and na-
tural arrangements, in the construction of the primary divi-
sions. It would have been of some advantage to the science,
had conchologists ascertained the use of the teeth in the
economy of the animal, before forming any divisions from
their presence, absence, or position. They do not appear
to be the index of any peculiar organization, neither can
they be employed to bring together naturally allied families.
The use of the adductor muscle is to close the shell ; the
ligament opens it;™andsthe teeth of the hinge seem destined
to modify and direct these movements. The characters
furnished by these three parts of the shell appear to be near-
ly of equal importance, and fit only to occupy a very subor-
dinate place. Were the circumstances connected with the
teeth of the hinge to become the foundation of the higher
divisions, many natural families would be broken. Thus,
the genus anodonta would be removed from the unio, al-
though they are both fluviatile, possess one long subulated
foot, one syphon in the form of a hole, the summit of the cloak
furnished with cirri, the branchiae in part re-united, vivipa-
rous, carrying the young in the branchiae. In short, it seems
to be a character fit only for] generic and specific distinc-
tions.

Bivalve shells have often been divided into equilateral
and inequilateral. These differences do not appear to be
the signs of any peculiar character of the animal, or any of
•its functions. They must influence, to a certain extent, the

72 MOLLUSCA.

relation between the different parts, but this influence is not
sufficiently obvious. The character thus furnished is of an
uncertain kind. It is influenced by the age of the indivi-
dual, and therefore can only be employed with caution in
specific distinctions.

The last character of the bivalves which we shall notice
is the power which some of them possess of piercing stones
and wood for the purpose of forming to themselves a retreat.
These are termed borers. It was supposed by many that
the animal secreted a liquor with which it dissolved the bo-
dies into which it penetrated, but the sagacious Reaumur
soon ascertained that the boring was performed by means of
a rotatory movement of the larger valves. M. Fleurieu-
Bellevue states, that the calcareous stone in which the ru-
pellaria lithophaga is found, is often discoloured in the im-
mediate neighbourhood of its recess. This may arise from
other secretions of the animal, or even from the stagnant
sea water in the hole, and not from the action of the phos-
phoric acid, or any other solvent supposed to be employed
by the animal. These would act'equally on the shell as on
the calcareous rock. But the borers are not confined to
calcareous rocks, they also lodge in slate-clay, and other ar-
gillaceous strata. This is very often the case with the Pho-
lades. But this character can never be extensively employ-
ed, as the same species which, at one time, may be found
imbedded in stone, will be observed at another seated among
the roots of sea-weed, or buried among gravel.

From the preceding remarks it will appear obvious, that
there are many characters furnished by the shell, which give
us indications of corresponding peculiarities in the structure
of the animal, and on that account ought to be employed in
every natural arrangement. These characters have this cir-

MOLLUSCA. 73

cumstance to recommend them, that they are obvious and
permanent. The objects which furnish them can be pre-
served in our cabinets, and serve to perpetuate our recollec-
tion of the appearances which the more perishable parts
have exhibited.

There is yet another class of characters to be considered,
very variously rated by different authors. These characters
are taken from the situation in which shells are found, whe-
ther on the land, in fresh water, or in the sea.

This mode of dividing testaceous bodies has not been
sufficiently attended to by conchologists, who have, in ge-
neral, condemned the plan, as founded upon an improper
principle, viz., the classification of animals from the places
which they frequent, instead of the forms which they exhi-
bit. Such a mode of arranging the higher divisions of the
different classes we would readily censure ; but when em-
ployed in the inferior subdivisions of the testacea, we regard
it as an important and a natural character. We ask the true
naturalist to say, which is the most important character, the
hinge having teeth or wanting projections, and the animal
residing in fresh water or in the sea? We anticipate with con-
fidence the preference which would be given to the latter,
although the decision might provoke a sneer in a mere col-
lector. Nature has evidently drawn a line of separation
between the three tribes, which it is not difficult to perceive.

The terrestrial testacea are destined to live on vegetable
matter. Their organs of respiration are suited to the me-
dium in which they reside. Their organs of feeling are, in
general, more numerous than those of the fluviatile or marine
shells. The tentacula of the latter seldom exceed two,
while in the land shells the tentacula are, in general, four in
number. The eyes are likewise differently placed ; in the

74 MOLLUSCA.

aquatic testacea they are situate on the head, at the base
of the tentacula; whereas the eyes in nearly all the terres-
trial species are placed on the tip of these organs. We might
also add, that no bivalve shells are found on the land ; they
belong exclusively to fresh water and to the sea.

The fluviatile shells, though destined to reside in a differ-
ent medium from the terrestrial, have in the greater number of
genera their organs of respiration (according to Cuvier) near-
ly the same, and are, therefore, compelled to come occasion-
ally to the surface to respire. They have usually two flat ten-
tacula, with the eyes placed at the base. They may, in general,
be distinguished from the marine kinds by the superior thick-
ness oftheir epidemics, their corneous colour, and semi-trans-
parency.

The marine shells are the most numerous, the most beau-
tiful, and the most highly prized of all the testacea. Many
of the univalves of this tribe possess a lengthened respira-
tory tube, with a canal in the shell for its protection, a cir-
cumstance not observed in the fluviatile testacea. There is
one circumstance which at once points out the difference in
structure between the fluviatile and marine testacea : the
fluviatile cannot live in salt water, nor the marine in fresh
water. This fact points out an arrangement in their orga-
nization to which conchologists ought to pay attention.

These remarks are calculated to persuade conchologists
to attend to the character furnished by the habitation of
shells. In the formation of genera, it ought to be respected ;
in the higher divisions it would be inconvenient. The care-
lessness of Linnaeus with regard to this character, is the prin-
cipal reason why his genus helix is such a confused and in-
digested mass. Were the distinction arising from habitation
to be observed in the distribution of the testacea, no confu-

MOLLUSCA. 75

sion could possibly take place. Some changes might be oc-
casioned by it, but much practical difficulty would be avoided.
Indeed, so useful is the distinction, that conchologists, with-
out avowing the propriety of the principle, have in many
instances observed it.

Having thus taken a short view of the different characters
employed by conchologists in the arrangement of the tes-
tacea, and endeavoured to ascertain their relative import •
ance, we shall conclude this part of the article by an appli-
cation of the principles we have established, to an examina-
tion of the Linnaean genera, and to an enumeration of those
genera which subsequent naturalists have formed, without,
however, attempting to give even an approximation to many
of the modern divisions, which have been multiplied beyond
all bounds ; as our present object is to convey to the reader
some farther remarks, illustrative of the history of the science,
rather than specific descriptions.

LINN^AN GENERA.

1. CHITON. — The only change which has taken place in
this genus, of any consequence, is its transference to the
naked cephalous mollusca, effected by Lamark. The inha-
bitants bear a near resemblance to those of the genus patella,
and belong to the order cyclcbranchia of Cuvier. The mar-
ginal ligament which connects the testaceous plates, even
after the extraction of the animal, is, in fact, the margin of
its cloak, and offers, in connection with the notches of the
plates, more certain and convenient distinctions for the dis-
tribution of the species, than the number or appearance of
the valves, a character exclusively employed by Linnaeus.

2. LEPAS — This genus has undergone several important

76 MOLLUSCA.

alterations since the days of Linnaeus. As originally con-
structed by that author, it contained shells which differ
widely from one another in habit and form. Bruguiere, the
celebrated French conchologist, separated the fixed shells
furnished with an operculum, under the name of Balanus,
and those which were seated on a peduncle, he retained un-
der the generic name Anatifer. He thus suppressed entirely
the Linnaean name of the genus. To the name of his first
genus, we have no objections, but the second, though it re-
cords a curious fact in the history of popular errors, lias been
injudiciously selected. The name Lepas has been retained
by the best British writers, who have described seven species
which live in our seas. These are distributed into two sec-
tions, according as the valves are five or more in number.
The Lepas anatifera is an example of the first division, and
the L. scalpellum of the second.

The genus balanus, as thus formed by Bruguiere, and re-
presented by the lepas balanus of Linnaeus, contained nine-
teen species. From these Lamark has separated the B.
diadema, testudinaris, and balanaris, to form his genus Co-
ronula. These shells are conical, and have the compart-
ments formed into twelve areae, six of these being depressed,
and six elevated. They chiefly inhabit the skin of the whale,
the base of the shell being placed in the fat. Lamark has
likewise formed another genus, from two species analogous
to the coronolulae, which he terms Tubicinella, and charac-
terises it thus : — " Testa univalvis, regularis, non spiralis,
tubulosa, versus basin attenuata, utrique truncata ; apertura
orbiculata terminali ; operculo quadrivalvi." The lepas stri-
ata of Pennant is now the representation of a new genus
termed Creusia.

M. Dufresne (Annales du Micseum, vol. i. p. 465), endea-

MOLLUSCA. 77

vours to prove by very inconclusive reasoning, that these shells
are formed posterior to the birth of the animal. He supposes
that, when they become too small to contain the inhabitants on
account of their increasing size, the old shells are forsaken, and
more commodious dwellings formed, until the animal reaches
its full size. Other proof, however, than what the author ad-
duces, is necessary to render the opinion probable.

Lamark, in his Systeme des Animaux sans vertebres,
placed these shells in a separate section at the end of the
bivalves, and among the acephalous mollusca. Afterwards
he considered them as constituting a particular division of
the crustaceous animals; and, lastly, he has assigned them
a place in his new class, which he terms CIRRHIPIDES.

3. PHOLAS. — This very natural genus was placed among
the multivalves by Linnaeus, in the twelfth edition of his
system. It is now united with the bivalves, the accessory
plates at the hinge being regarded as of subordinate import-
ance. In other respects it has stood the test of modern in-
novation, with the exception of the genus GASTROCIOSNA
of Spengler, in which the teeth are obsolete. This includes
the pholas hians of Chemnitz, and the mya dubia of Pen-
nant.

4. MYA — If we consider as definite the character as-
signed to this genus by Linnaeus himself, we shall find that
it excludes many species which differ from the M. truncata>
at present considered as the type of the genus. In this
shell, the valves gape at both extremities, the ligament is
internal, and placed on a thick erect tooth in one valve,jnot
inserted into the opposite side. As the M. vulsella of Lin-
naeus is close at both ends, and destitute of a tooth, it has
been separated from the true myae, and formed into a dis-
tinct, genus by Lamark, under the title VULSELLA. This

78 MOLLUSCA.

shell presented some difficulty to Linnaeus, as he placed it
at first among the Pinna, and afterwards among the Myce.
Even Bruguiere gave it a place among the oysters.

Another genus has been formed by Lamark from the mya
siliqua of Chemn. (Conch.vol.*i. p. 192, tab. 198, fig. 1934).
He calls it GLYCIMERIS. Though nearly related to the true
myae, by gaping at both extremities, yet it differs from them
in the hinge, which is destitute of teeth, and in the ligament
being external.

« A new genus was formed by M. M. Groye, (Annales du
Museum, vol. ix.), which he terms PANOPEA, and assigns
to it the following characters : — " Coquille transverse, bail-
lante inegalement au deux bouts, charniere semblable dans
Tune et dans Tautre valve, ayant une callosite ou grosse dent
allongee, placee en avant et sur le corselet ; decurrente sur
le bord interieur, relevee en arete, mousse et saillarit poste-
rieurement ; une dent cardinale conique un peu comprimee
et arquee, et sur le valve droit une fosette dans laquelle s'en-
grene la dent de la valve opposee ; ligament exterieur, cro-
chets peu protuberans, corselet large, deux impressions
musculaires dans chaque valve situees vers les extremites."
The type of this genus is the mya glycimeris of Gmelin first
noticed by Aldrovandus. It is inserted among the British
shells by Mr. Donovan upon very slight authority. In the
construction of the genus, we think, that M. Groye has acted
properly, but there was no necessity surely for changing the
trivial name (of the first described species) bestowed upon
it by the discoverer. He has added another species from
Monte Pulgnasco in Parma. In the trivial name of this
species, we consider that he has been guilty of an act of
injustice. He has called it P. Faujas, in honour of Faujas
St. Fond, the zealous Professor of Geology in the Museum

MOLLUSCA. 79

of Natural History at Paris. But the truth is, that it was
found by M. Cortezi, Counsellor at Parma, and a success-
ful investigator of the organic remains of that district. It
ought, therefore, to have obtained the name of P., Cortezi,
in honour of the discoverer, instead of the name of Faujas
St. Fond, who received it from M. Cortezi, and whose sole
merit in the subject consisted in his bringing it in safety
to Paris.

The principal error of Linnaeus in the construction of this
genus, consisted in the insertion of fluviatile shells among
his marine species. Bruguiere readily perceived this error,
and formed a new genus for their reception, which he called
UNIO. But this group, now denominated NAYADES by La-
mark, includes the genera unio hyria, anadonta tridina, and,
we may add, alasmodon.

5. SOLEN. — This genus has undergone few changes since
the days of Linnaeus. . The character has been somewhat
restricted, and those species have been removed, in which
the external margin is a little arcuated, and the cardinal
teeth articulated, and two in number, and formed by Lamark
into a new genus, which he terrns SANGUINOL.ARIA. The
animals of this genus, according to Poli, differ from the so-
lens, in having the tubes of the syphon separate, and of
unequal length and thickness. The 8. minutus of Linnaeus,
found in our seas, is referred to the genus HIATEKLA by
Cuvier, a genus very imperfectly defined, but nearly allied
to, if it be not identical with, the byssomia of the same au-
thor, which includes the mytilus rugosus of Linnaeus.

6. TELJLINA. — This extensive genus of Linnaeus, the es-
sential character of which is to have an anterior inflection
or fold in each valve, and lateral teeth, includes many shells
which differ greatly in form and habit, and which disagree

80 MOLLUSCA.

even with his own definition. Hence several important im-
provements have taken place in the distribution of the species.

The first change in the genus of any consequence con-
sisted in the separation of the fluviatile from the marine
species. This was accomplished by Scopoli, (Introd. ad
Hist. Nat. 397), who bestowed on them the generic name
of SpJuerium. Bruguiere afterwards wantonly changed the
name to CYCLAS, and this change has been embraced by
Lamark and other naturalists*

Another new genus of fluviatile shells, allied to the pre-
ceding, has been formed by Bruguiere and Lamark for the
reception of one species. The genus is termed GALATKEA,
and the species G. radiata. There are two approaching
hinge-teeth in the right valve, with a cavity in front, and
two distant hinge-teeth in the left, with an intermediate
large grooved callosity. The lateral teeth are of consider-
able size. The ligament is external, and the muscular im-
pressions are two in number, and lateral.

The Tellina incequivalvis presents characters which read-
ily distinguish it from the other species with which Linnaeus
placed it. The shell is inequivalve and inequilateral ; the
ligament is internal, and the lateral laminae are wanting.
Besides, the animal differs from the other inhabitants of the
tellinae, and is nearly related to the solens. Hence Brugu-
iere formed a new genus for its reception, which he termed
PANDORA.

There are several species of the genus telling and Venus,
which Bruguiere and Lamark have formed into a separate
genus called LUCINA, which is thus characterised : — " Testa
bivalvis. aequivalvis, orbiculata, vel ovato transversa ; nati-
bus arcuatis, postice versis. Cardo dentibus cardinalibus
1 . s. 2. variabilibus ; lateralibus 1 . s. 2. remotis, interdum

MOLLUSCA* 8 1

subnullis." To this genus Lamark brings the Tellina lactea
and divaricata of Linnaeus, and the muricata of Chemn.
(Conch, vol. xi. p. 209, tab. 199, fig. 1945-6), together with
the Venus fimbria ta, and Pcnsylvanica of Linnaeus, and the
Jamaicensis of Chemn. (Conch, vol. vii. p. 24, tab. 39, fig.
408-9). Cuvier, however, has restored the T. lactea to the
genus Loripes, which Poli instituted for its reception.

7. CARDIUM. — This is, perhaps, the best constructed
genus which Linnaeus formed. The characters are definite
and obvious, and all the species are naturally allied. Hence
few changes have taken place in their arrangement. The
animal constitutes a new genus in the system of Poli, which
he terms cerastis.

Cuvier is disposed to constitute a new genus under the
title HEMICARDIA, for the reception of the C. cardissa of
Chemn., commonly called the Venus-heart cockle. The
truncated appearance on the one side, and its being carin-
ated in the middle, point out a conformation of the inhabi-
tant different from the true cockles. Of this new genus we
possess some fossil species.

8. MACTRA. — The ligament, in the marine bivalves, is,
in general, placed on the outside, but in this genus, of which
Lamark has formed his family mactreacea, the ligament
is internal, and inserted in a cavity at the hinge formed for
its reception. This family, as it stands at present, contains
several well characterised genera.

In the restricted genus, MACTRA, as represented by the
M. stultorum of Linnaeus ; the shell gapes a little, and the
lateral teeth are strong, and lock into each other. ..Th-j
shells with age arrive at a considerable thickness. The in-
habitant belongs to the genus callista in the system of Pcli.

The genus CRASSATELLA of Lamark contains shells which

82 MOLLUSCA.

close exactly, and have the lateral teeth obsolete. He de-
scribes seven fossil species, and eleven recent ones, viz.
mactra glabrata, (Encyclopedic Meth. tab. 257. fig. 3) ; ve-
nus divaricata of Martini, (Conch, vi. p. 318. tab. 30. fig.
317, 318,) under the title Crassatella contraria ; and the
following new species, rostrata, Kingicola (from King's Is-
land!) donacina, sulcata, subradiata, erycincea, cycladea,
and strata.

The genus ERYCINA is composed entirely of fossil species.
Lamark has assigned it the following character : " Testa
bivalvis, equivalvis, inequilatera, transversa. Dentes car-
dinales bini, superne divergentes, cum foveola minima in-
termedia : laterales compressi oblongi. Ligamentum fove-
ola cardinal! insertum." From the situation of the ligament
being inserted in the small space between the teeth, the pit
or cavity is less than in any of the other genera. The mus-
cular impressions are two in number.

The transverse mactrae, which gape, but are destitute of
lateral teeth, such as the M. lutraria of Linnaeus, compose
the genus LUTRARIA of Lamark. The species already men-
tioned, and the mya oblonga of Gmelin, or mactra hians of
Montagu, occur on our coasts ; the former in great abund-
ance at the mouths of the European rivers.

The genus UNGULINA, formed by Daudin, contains only
one species, existing in the cabinet of Favanne. It is un-
certain from what country it came. It is a regular longi-
tudinal shell. The hinge is formed by one small tooth be-
tween two oblique pits. The muscular impressions are two
in number. It is figured in Deterville's edition of Buffon.
{Hist. Nat. des Coquil. torn. xx. f. 2, 3.)

Another genus established by the same author, and termed
ERODONA, is subtransverse, irregular, and gaping, the hinge,

MOLLUSCA. 83

in one valve, consisting of one hollowed tooth, and in the
other a depression between two eminences. It includes
two shells from the cabinet of Favanne. It is intermediate
between the mactrae and nayae.

9- DONAX. The shells of this genus are readily Imown
at first sight by their singular cuneiform shape. The hinge
teeth are two in number, and the lateral teeth are spread-
ing. The ligament is external, and, like the tellinae, it is
placed on the shortest side. This is a circumstance of rate
occurrence among the inequivalve testacea. The animal
belongs to the genus peronaea of Poli.

Lamark has instituted a genus nearly allied to the pre-
ceding, termed PETRICOL.A, the shells of which gape a little
at both «nds. There is one hinge tooth in one valve, and
a bifid one in the other. The ligament is external ; the
muscular impressions are two in number ; the structure of
the hinge teeth, and the absence of the lateral teeth, at once
distinguish this genus from the donax and venus. These
animals are likewise peculiar in their habits. Lamark quotes
the venus lithophaga of Retzius, Act. Acad. Tour. vol. iii.
p. 11, and the venus lapicida of Chemn. Conch, x. p. 356.
tab. 172, f. 1664-5. But Lamark's genus has been again
altered by Fleurieu-Bellevue, who has formed his genus
RUPELLAHIA, from the V. lithophagus of Retzius, and an-
other species termed striata. (Mem. de VAcad. de la Ro-
chelle, ii. tab. ii, fig. 9.) In this genus the shell is transverse
and inequilateral, compressed in the anterior part, and
swollen behind. There are two crooked hinge teeth on
each valve, one simple, the other bifid. The ligament is
external, and there are two muscular impressions. The
donax irio belongs to this genus. The same author has

84 MOLLUSC A.

formed two other genera of borers. The first he terms Ru-
PICOLA, having a transverse inequilateral shell) a little gap-
ing at the ends ; no teeth or callosities. In an internal
projection of each valve, there is a pit for the ligament.
The other genus is named SAXICAVA. It is transverse,
inequilateral, and gaping, without teeth, or callosity, or pit.
The ligament is external.

10. VENUS. This Linnaean genus contains so many
species, that there is considerable difficulty in studying it.
The formation of new genera, from its members, by dimi-
nishing their numbers, must prove highly acceptible to the
student of conchology. Lamark has succeeded so far by
previously restricting the character of the original as fol-
lows : " Testa bivalvis aequivalvis, binaequilatera transversa
vel suborbicularis. Dentes cardinales tres in utroque val-
va, ad nates basi convergentibus. Ligamentum externum,
nymphas labiaque obtegens." The three diverging hinge
teeth constitute the essential character of the genus, so that
Lamark has been able to form three other genera from dif-
ferent characters.

The genus CYTHEREA (the meretrix of Lamark's Sys-
teme des Animaux) is thus characterised : " Cardo dentibus
duobus tribusve approximatis, basi convergentes ; uno soli-
tareo remotiuscula sub ano." It must be confessed that the
insulated teeth under the lunule, in the absence of other
characters, is obviously artificial. This genus contains
many species requiring subdivision.

The genus VENEBICARDIA, formed for the reception
of some fossil species, is thus defined : " Testa bivalvis,
aequivalvis, inaequilatera, extus longitudinaliter costata. Den-
tes cordinales sub-bini crassi oblique secundi." The num-

MOLLUSCA. 85

her of hinge teeth, and the longitudinal ribs, readily distin-
guish it from the genus Venus. It is very limited in recent
species.

Another genus instituted by Lamark, and termed by him
CAPSA, has two teeth in one valve, and a bifid tooth in the
other, the type of which he considered to be the donax lavi-
gata of Gmelin,

It was in the construction of the characters of the genus
Venus that Linnaeus unfortunately indulged in obscene al-
lusions. It is now time that the pages of natural history
were freed from such pollution. Other names, more expres-
sive, can easily be substituted, alike advantageous to the in-
terests of science, and the reputation of the illustrious Swede.
11. SPONDYLUS — The shells which Linnaeus included
under this head are usually denominated prickly oysters.
The genus represented by the <S. gcederopus of Linnaeus.
The S. plicatula of the same author has been separated
from the spondyli, and placed in a new genus, under the
name PLICATULA. This genus differs from the former in
the valves wanting ears, and in the absence of the triangu-
lar unisulcated space at the teeth of the under valve, so
characteristic of the parent genus.

12. CHAMA. — This is by no means a well constituted
genus in the Linnaean system, as it includes shells possess-
ing very different characters. It has, accordingly, under-
gone several important alterations. Bruguiere proceeded
so far by establishing two new genera, and Lamark, follow-
ing the same plan, has added three more to the number.
Those shells, which now belong to the genus CHAMA, are
irregular, inequivalve, and adhere to other bodies. The
hinge contains only one thick oblique tooth. It is repre-
sented by the chama Lazarus of Linnaeus.

86 MOLLUSCA.

The genus CARDITA, of Bruguiere, represented by the
C.variegata, (Lister, tab. 344, fig. 84.,) consists of equivalve
free shells, with the hinge furnished with two unequal teeth,
the one situated under the beak, the other lateral, under
the anterior margin.

The chama cor of Linnaeus appeared to Lamark possess-
ed of sufficient characters to constitute a distinct genus,
which he has named ISOCARDIA. It is an equivalve, free,
regular, heart-shaped shell, with two cardinal teeth, and a
separate lateral one, with separate, diverging, involuted
beaks. It is an inhabitant of the British Seas.

To Bruguiere we owe the institution of the genus TRI-
DACNA, which is represented by the chama gigas of Lin-
naeus, the largest shell in nature. The shell is equivalve
and free. The hinge consists of two compressed teeth, and
there is a gape at the lunule.

From the preceding genus of Bruguiere, Lamark has se-
parated the chama hippopus of Linnaeus, and formed from
it a new genus, which he calls hijqpopus. In its hinge it
resembles the tridacna, but differs in the structure of the
lunule, which in this is closed.

The genus DICERAS of Lamark, which he formed from
the chama bicornis of Bruguiere, approaches the isocardia
in appearance, but the following character which he assigns,
is fully sufficient for their discrimination : " Testa bivalvis
inaequivalvis, adherens : natibus conicis, maximis, divergen-
tibus, in spiram irregularem contortis. Dens cardinalis
maximus, crassus, concavus, auricularis in valvula majore.
Impressiones duo musculares." It occurs only in a fossil
state.

Before dismissing this Linnaean division of shells, we must
notice another genus which has been added to it by Lamark,

MOLLUSC A. 87

from species brought from the Indian Seas. He terms it
etheria, and originally described its generic character in the
following words : " Coquille bivalve, inequivalve, irreguliere,
adherente, a crochets court, enfonces dans la base des
valves et deriges de cote. Charniere sans dent ; deux im-
pressions musculaires separees et laterales. Ligament demi-
interieur, enveloppant une callosite oblongee, et sortant en
dehors par une fissure recourbee." He has described four
species which are very rugged on the outside, but finely
nacred within, and has placed the genus in his family ca-
macea, while in external aspect, and in the absence of
teeth, the species make a near approach to the ostreacea.

\ 3. ARC A. Linnaeus assimilated, under this genus, every
shell the hinge of which presented numerous mutually inserted
teeth. The shells which were thus united, have numerous re-
lations, and constitute a very natural family. But in this family
there are several groups of which Bruguiere formed sections
and Lamark genera. The genus area is now restricted to
those shells in which the hinge is in a straight line, and
composed of numerous small lamelliform teeth, without la-
teral ribs. They have obtained their name from their re-
semblance to a ship, when the shell is inverted. Many
species of this genus gape a little at the superior margin, to
enable the animal to send out those tendinous threads by
which it adheres to the rocks. The A. lactea, note, tetra-
gona, barbata, andfusca, are natives of the British Seas.

The Linnaean arcae, which have the hinge line broken
and angular, belong to the genus NUCULA. In this genus
the beaks are contiguous and turned a little backwards. The
nucula, nuclea, minuta, rosfrata, and tenuis, are found on
our shores.

In the genus PECTUNCULUS, the hinge teeth are situated

88 MOLLUSCA.

on a curved line, the shell is nearly orbicular, and the mus-
cular impressions, which are two in number, form each a
callous projection with a sharp margin. The area pilosa> a
native of Britain, is referable to this genus.

In the genus CUCULLJEA, the teeth of the hinge are simi-
lar to the arcae, but at each extremity there are three or
four transverse parallel ribs. It is represented by the area
cucullata of Chemn. (Conch, vii. p. 174. tab. 55. f. 526-528,)

To the family arcacea, Lamark, at one period, added
the genus which he terms TRIGONIA. The hinge teeth are
only two in number, diverging and compressed, but they
are transversely grooved on each side. The muscular im-
pressions are two in number in the recent species, T. pec-
tinata, but in some of the fossil shells referred to in this ge-
nus, Mr. Sowerby could observe only one. The trigonia
now forms along with castalia, the small family of Trigonees
formed by Lamark at the suggestion of M. Valenciennes.

14. OSTREA. — Linnaeus, in the construction of this ge-
nus, brought together many shells totally dissimilar in form,
character, and habit, and hence it has undergone great al-
terations in the hands of succeeding conchologists. To as-
sociate in one genus shells which remain immoveably fixed
to the rocks and stones from their birth, and which exhibit
few other signs of vitality than the opening and shutting of
their valves, with those which possess a locomotive power ;
to unite such as are irregular in their form and imbricated
in their structure, with such as are of regular gro wth and
solid texture, might surely be regarded as a violation of all
the laws of a natural or an artificial system. Yet of such
incongruous materials is the Linnaean genus ostrea compos-
ed, which, in spite of all its imperfections, has still its ad-
mirers in this country. (See Descriptive Catalogue, Lin.

MOLLUSCA. 89

Trans.) The first important improvement in the reforma-
tion of the genus, consisted in the separation of the pec-
tens, which was executed by Pennant, and afterwards by
Bruguiere and Lamark. Since new characters have been
assigned to the genus ostrea, other separations must take
place. It is thus defined : " Testa bivalvis inaequivalvis,
rudis adhaerens ; cardine edentulo. Fossula cardinalis ma-
joris valvae setate crescens. Ligamentum semi-internum.
Impressio muscularis unica." The genus may be divided
into two sections ; the first having the margin of the valves
simple, as the common oyster ; and in the second the mar-
gins are plaited, as in the O. crista-gallL

In consequence of this change in the generic character,
the ostrea malleus of Linnaeus, (Lister, tab. 219, f. 54.,) has
been formed into the genus MALLEUS. The shell is free,
gapes a little at the beaks, produces a byssus, has no teeth
in the hinge but a conical pit for the insertion of the liga-
ment, placed obliquely on the margin of each valve. It
was for a long time highly prized by collectors.

The genus PECTEN is one of the best characterised, most
natural, and most beautiful, in the system. The shell is
inequivalve and regular, the hinge is destitute of teeth, and
the internal ligament is fixed to a triangular cardinal cavity.
There are fourteen species natives of our shores.

From the ostrea perna, ephippium^ and isogonum, Bru-
guiere formed the genus PERNA. The hinge is linear, and
cut into a number of lengthened parallel veins, which re-
ceive the ligament. The interstices are formed into teeth,
which simply oppose those of the* other valve. In the an-
terior side of the valve, near the beaks, there is a callosity,
and an opening for the byssus of the animal.

Lamark has constituted another genus, nearly allied to

90 MOLLUSCA.

the pernae, which he styles CRENATULA. The hinge in this
genus presents only a row of pits for the ligament, which
makes it appear crenulated. The intermediate spaces are
not formed into teeth, neither is there any callosity, or
opening for the byssus. He has figured two new species,
which he terms avicularis and mytiloides, and a third is the
ostrea picta of Gmelin, (Chemn, Conch, vii. p. 243. tab. 38.
f. 575.)

Nearly related to the pectens is the genus LIMA of Bru-
guiere. The species differ, however, in the ligament being
in a great measure on the outside. They are all of a white
colour. The ostrea lima is considered as the type of the
genus.

The genus PEDUM of Bruguiere differs from the preced-
ing in the ligament being external, a»d attached to a long
straight fissure. The ostrea spondiloidea of Chenin. { Conch.
viii. t. 72. fig. 669? 670,) is considered as the type of the
genus.

To this family we must add two genera, possessed of very
singular characters. They have neither hinge nor ligament.
The first, instituted by the celebrated botanist, Commer-
son, is termed ACARDO. The valves are depressed and
nearly equal, and held together by the adductor muscle.
The species at present known come from the eastern coast
of Africa. The second is termed radiolites, and was insti-
tuted by Lamark. It differs from the former in the form
of the valves, the inferior being turbinated, and the supe-
rior convex or conical. The species occur only in a fossil
state, and Irave been long known to geognosts under the
title ostracites.

15. ANOMIA. In the Linnaean system, this genus is equ-
ally faulty as the last. It contains many species, which

MOLLUSCA. 91

differ greatly from one another and from the generic char-
acter. Some are found recent on our shores, while others
occur only in a fossil state. Lamark, having rectified the
Linnaean character of the genus, has separated many species,
now grouped, into distinct genera. In the restricted genus
ANOMIA, the under valve has a hole or groove near the
beak, which is closed by a testaceous operculum. This ap-
pendage is fixed to rocks or stones, and has a ligament at-
tached to it.

In the genus CRANIA, represented by the Anomia crano-
laris of Linnaeus, the under valve is pierced by three holes,
which are oblique and unequal. The genus GRYPHJEA was
constituted from the Anomia Gryphus of Linnaeus. The
inferior valve is concave, terminating in a spirally involuted
beak, projecting upwards ; the upper valve is small, and re-
sembles a lid. A transversely striated pit at the hinge con-
tains the ligament. The only recent species known is called
G, angulata. Many species are found in a fossil state in
the rocks of this country.

Among the Anomia, Linnaeus placed the shells which
compose the genus TEREBRATULA, the characters of which
are so obvious and distinct. In this genus, which is inequi-
valve and regular, the beak of the larger valve is produced,
and pierced with a hole, through which the ligament of ad-
hesion passes. From the great extent of this genus in fossil
species, several subdivisions have been proposed.

From the Anomia placenta of Linnaeus, Lamark has form-
ed his genus PLACUNA. The hinge is remarkable for two
teeth on the one valve, placed like the letter V, the base
toward the beak, and two impressions on the other valve.
It occurs in the Indian Seas. The natives polish it for or-
naments.

92 MOLLUSCA.

To Lamark we are also indebted for having formed the
genus CALCEOLA from the anomia sandalum of Linnaeus.
The largest valve is sandal-shaped, and has at the hinge two
or three small teeth. The other valve is small, flat, semi-
orbicular, and resembles an operculum. It is frequent in a
fossil state in Germany.

Mr. Sowerby, in his valuable work on British Mineral
Conchology, has made us acquainted with several new
genera of fossil shells, which, by the older naturalists, would
have been inserted in the genus Anomia. The genus PEN-
TAMERUS is an equal-sided inequivalve bivalve, with one
valve, divided by a longitudinal internal septum into two
parts, the other by two septa into three parts or valves. Beaks
incurved, imperforate. He has figured three species of this
curious genus.

The genus PLAGIOSTOMA of Sowerby, is represented by
the Pectenites Plagiostomus of Luid, (tab. 10, f. 639,) and
is thus defined : " An oblique eared bivalve, hinge destitute
of teeth or internal pit. Line of the hinge straight in one
valve, in the other deeply cut by an angular sinus." He
gives figures of two species in his first volume, the gigan-
tea and the spinosa ; and many others have been subse-
quently detected.

The genus DIANCHORA is nearly related to the preced-
ing, but in this the shell is fixed, and the attached valve has
an opening in place of a beak. The other valve is beaked
and eared.

The anomia spinosa of Linnaeus probably belongs to Mr.
Sowerby's genus PRODUCTUS, which he thus defines : " An
equilateral unequal-valved bivalve, with a reflexed, more or
less cylindrical margin ; hinge transverse, linear ; beak im-
perforate ; one valve convex, the other flat or concave ex-

MOLLUSCA. 93

ternally." But many new genera must be instituted, to
embrace all the fossil species which would have been re-
ferred by Linnaeus to the genus Anomia.

16. MYTILUS. Before proceeding to notice those new
genera which have been formed from the Linnaean mytili,
we may state, that the three parasitical species of the Sys-
tema Naturce, belong to the genus Ostrea, to which they
have been transferred by late authors. But improvements
of a more important kind have been effected. Linnaeus had
associated together in this genus both fluviatile and marine
shells- The former now constitute a very natural genus
termed ANODONT A, formerly referred to, of which the British
rivers furnish several species. The muscular impressions
are three in number.

It was easy to perceive that the mytilus hirundo of Lin-
naeus did not belong to the true mussels, it being an in-
equivalve shell. Accordingly Lamark has constituted a new
genus for its reception, which he terms AVICULA. The
mytilus margaritiferus of Linnaeus is of this genus.

Lamark, by restricting the characters of the genus myti-
lus to include such species as have the beak terminal, has
in this manner separated the transverse species to form the
genus MODIOL.A. The mytilus modiolus of Linnaeus is the
type of the genus. It is common on the British shores,
together with the modiola discors and discrepans. We are
at a loss to account for the scruples of Lamark (Annales
de Museuss, vol. x.) about considering this genus as byssi-
ferous. Had he ever examined the figure of the type of
the genus in tab. 53 of Zoologia Danica, all his doubts
would have been removed.

17. PINNA. No changes have taken place in this Lin-
naean genus, except that a few new species have been added.

94 MOLLUSCA.

' In the course of our review of the Linnaean genera of
bivalves, we have exposed some of those errors which the
Swedish naturalist committed in associating discordant spe-
cies under the same genus. Perhaps our examination of
the univalves will make us better acquainted with the im-
perfections of that system, and dispose us to prize those im-
provements which subsequent naturalists have introduced.

18. ARGONAUTA. This genus, which contains but few
species, is highly prised by collectors, who call the princi-
pal species by the name of paper nautilus. By restricting
the characters of this genus, so as to embrace only those
species in which the opening is interrupted by the involu-
tion of the spire, and in which the dorsal ridge is double,
Lamark has been able to form the genus CARINARIA. In
tli is the mouth is entire, and the dorsal ridge single. It is
represented by the argonauta v.itrea of Gmelin.

1 8. NAUTILUS. Since the days of Linnaeus, our know-
ledge of the multilocular testacea has been greatly enlarg-
ed. He contented himself with arranging all the species
with which he was acquainted under one genus, but, in con-
sequence of modern industry, even the genera exceed the
number of Linnaean species. Many recent species have
been discovered by the aid of the microscope, among the
sand on the sea shore, and a still greater number in a fossil
state among the calcerous strata. These newly discovered
kinds exhibit many different characters, and have compell-
ed conchologists to institute so many new genera for their
reception, that the genus Nautilus of Linnaeus appears rather
as the head of a family or order, than as a separate genus
of univalve shells. In this department the names of Bru-
guiere, Lamark, Montfort, Parkinson, and Sowerby, deserve
respectful notice ; and it is from their writings that the fol-

MOIXUSCA. 95

lowing remarks concerning the multiloeular testacea have
been extracted. The multiloeular testacea may be divided
into three sections ; the first including those which are ob-
viously spiral ; the second, those which are produced ; and
the third, those which are of a globular or lenticular form.
These sections are merely provisional, and are only intend-
ed to render more obvious and intelligible our notices of
the genera.

1 . The spiral multiloeular testacea. At the head of this
first division stands the modern genus NAUTILUS, in which
the turns of the spire are contiguous, and the last whorl in-
closes the others. The partitions are perforated by a tube.
We possess on our shores several species of this genus, of
which the N. crispus is the most common.

In form, the genus LENTICULINA is nearly related to the
former. The margin of the mouth reaches to the centre
of the shell on both sides, and the partitions are destitute
of a syphon. Lamark is in possession of a recent shell of
this species from the sea near Teneriff.

The shells which Mr. Sowerby, in his Mineral Concho-
logy, has figured under the genus ELLIPSOLITHES, have the
whorls conspicuous, although the mouth clasps the body
whorl. But it is easily distinguished from the other genera
with which it is related by its elliptical form.

The genus DISCORBIS of Lamark (formerly called by him
Planulites) bears a considerable resemblance to the nauti-
lus in form, but the whorls are all apparent, and the parti-
tions entire.

In the genus ROTALIA, the spires approach to a conical
shape, and the marginated trigonal aperture is reflected to-
wards the base of the shell. It consists of shells which are
now found in a fossil state*

96

MOLLUSCA.

The nautilus spirula of Linnaeus has afforded characters
for the construction of a new genus termed SPIRULA. The
whorls are separate, the mouth orbicular, the partitions per-
forated by a tube, and the last turn of the spire prolonged
in a straight line. This last character was unknown to Lin-
naeus, who had only seen the spiral body of the shell.

The genus SPIROLINA has the last turn of the spire pro-
duced like the preceding, but the whorls are contiguous.
The partitions are perforated by a tube.

The genus LITUOLA is allied to the spirula and spirolina
in the production of the last whorl. The spires of the body
are contiguous, and the partitions are pierced by a number
of holes.

In the preceding genera the inner walls of the cavity are
simple ; but in the two following, the walls are formed into
joints by sinuous sutures. The first of these is the AMMO-
NITES, including those shells which have been termed cor-
nua ammonis. The origin of this name is, by some, sought
for in their resemblance to the horns of a ram ; by others,
to their having been found near the temple of Jupiter Am-
mon in Upper Egypt. By the Indians, the ammonites
sacer is considered as a metamorphosis of the god Vishnu,
and termed by them salgram or salgraman. It is found
among the peebles of the Gandica where it joins the Gan-
ges. In this genus the whorls are contiguous, spiral, de-
pressed, and obvious. '

The ORBULITES of Lamark differs from the ammonites
in the circumstance of the last whorl embracing and con-
cealing the others. In both the syphon is marginal.

Nearly allied to the preceding is the TURRXLITES of
Montfort. It is similar in internal structure, but while the
shells of the former are spirally discoid, those of the present

MOLLUSCA. 97

genus are spirally turreted, resembling a Turbo or Turri-
cula. Several species are figured by Sowerby in his Mine-
ral Conchology.

The genus SCAPHITES, formed by Parkinson^ possesses
very peculiar characters. It commences with a depressed
volution, the last turn of which, after being enlarged and
elongated, is diminished and reflected inwards.

2. Multilocular testacea with the shell produced. It
must be confessed, that the genera of this section are but
imperfectly understood. The recent kinds are too small to
admit of any investigation of the animal, so that we are
left entirely to conjecture.

The genus HIPPURITES is of a conical form, and either
straight or crooked. Within it is transversely chambered,
and furnished with two lateral, longitudinal, obtuse, con-
verging ridges. The last chamber is closed by an operculum.

In the ORTHOCERA the shell is straight or slightly bent,
and conical. The chambers are distinct, and pierced with
a tube. We possess on our shores many minute species of
this genus,

The genus BACULITES of Faujas St. Fond possesses a
structure similar to the ammonites, the inner walls being
articulated with sinuous sutures, and the partitions perfor-
ated. The shell is fusiform or bent into two parallel limbs.
Mr. Parkinson has contributed greatly to our knowledge of
this genus, and has termed it Hamites. We prefer the name
of the original discoverer to that of our English naturalist,
which is very faulty. For, according to Pliny, " Hammites
ovis piscium similis est."

In the BELEMNITES the shell is straight, conical, pointed,
solid at the summit, and furnished with a lateral gutter.
There is seldom more than one of the cells apparent, of a

93 MOLLUSC A.

conical form, the older ones having been effaced in succes-
sion. The genus Tulaxodes of Guettard is not, perhaps,
entitled to be considered as distinct.

The AMPLEXUS of Sowerby belongs to this division. It
is nearly cylindrical, divided into chambers by numerous
transverse septa, which embrace each other with their re-
flected margins. It contains one species from the limestone
rocks of Ireland, but we may add that it has been supposed
to belong to the zoophytes rather than the mollusca.

3. Multilocular testacea of a globular form. The first
genus of this section is the MILIOLA. The shell is com-
posed of three or four oval cells, turning round an axis pa-
rallel to their longest diameter. Many recent species of
this genus are common on our shores ; they were included
by Montagu in his genus vermiculum.

In the RENULINA the cells are narrow, linear, unilateral,
curved into a part of a circle, and all situate on the same
plane. The smallest cell forms a little arch round a mar-
ginal axis, and the others are placed contiguous to this on
the same side, The species are all fossil.

The GYROGOXA was for many years viewed as a shell of
a spheroidal form, composed of linear, curved, grooved,
pieces, terminating in two poles, the external surface obliquely
spiral, the spires terminating at each pole, and as found only
in a fossil state. But more recent observations have con-
nected it with the seed vessel of the genus chara.

The shells of the genus NUMMULITES are remarkable for
their lenticular form. The external surface is smooth, and
the cells concealed, but internally the transverse shells are
disposed in a spiral discoid form. The cells are imperfor-
ate ; they are the camerinae of Bruguiere, the helecites of
Guettard, and the discolithes of Fortis. This last author

MOLLUSCA. 99

supposes, that they are formed in the interior of an animal
analogous to the sepia. The same opinion may, with pro-
priety, be entertained of many other genera of multilocular
testacea. Faujas St. Fond found a recent specimen of a
nummulite among the fragments of the corallina officinalis,
brought from the island of Corsica.

It is probable that the genus LAGENA, formed from the
serpulae lagence of Walker's Testacea minuta Rariora, be-
longs to the multilocular testacea ; as in some of the species
we have observed the appearances of internal, divisions.

As connected with this division of the Linnsean genera,
we may take notice of the British shell called by Lightfoot
Nautilus lacustris, (Phil. Trans. Ixxvi. tab. 1). The very
circumstance of its being a fresh water shell, distinguishes
it sufficiently from all those which we have been consider-
ing, and its other characters are likewise peculiar. The
partitions are distant, and consist of three testaceous plates,
not united, which leave a sufficient opening between them
to allow the animal to protrude and withdraw itself. It con-
stitutes a distinct genus, which has been termed SEGMEK-
TINA, from the trivial name bestowed on it by Solander,
which refers to the structure of the septa. Its place in the
system is next to the genus planorbis.

These genera of multilocular shells which we have enu-
merated, are those which have been established with the
greatest attention. Many other genera might have been
enumerated, particularly those formed by Montfort, but the
character given of them by Cuvier will satisfy the curiosity
of the reader. When speaking of the Conchyliologie $ys-
tematique of that author, in reference to this subject, he
says, " Ou presque toutes les especes et meme des varietes
sont erigees en genres."

100 MOLLUSCA.

19. CONUS. — Tliis genus is so very natural, that it has
undergone no changes since the days of Linnaeus, except by
the addition of new species. That author was acquainted
with thirty-five species and a few varieties ; but M. Hawss
communicated to Bruguiere descriptions of one hundred and
forty-six, from specimens existing in his own cabinet. We
cannot boast of any British species.

20. CYPRJEA. — This genus is equally natural as the for-
mer. It has undergone no change since the days of Major.

21. BULLA. — This genus presents to the mere conchologist
a source of great perplexity. It displays at once the absurdity
of dividing the molluscous'animals in to testaceous and naked,
since no such distinction is observable in nature. Many of
the shells which were formerly included in this genus are
found to be contained writhin the common integuments of
the animal. It was this circumstance which induced Lin-
naeus to separate the limax and the aplysiafrom the vermes
testacea. Both of these have shells, but they are concealed.
In imitation of the same principle, Lamark has formed a new
genus among the naked mollusca, called BULLJEA, for the
reception of those bullae in which the shell is concealed.
The bulla aperta is the type of the genus. The bulla plu-
mula of Montagu is another shell included in the animal,
which is very closely connected with the genus Pleuro-
branchia of Cuvier. (Annales du Mus. v, 269). It may be
asked, are all the other bullae found in similar situations, and
consequently do they belong to the naked mollusca ? La-
mark considers, and apparently with reason, that all those
which are distinctly spirally involuted, and ornamented with
colours, are not entirely inclosed in the cloak of the animal,
and ought therefore to be ranged with the testaceous mol-
lusca. How few British species does this character include.

MOLLUSCA. 101

As originally constituted, the genus of Linnaeus contain-
ed species of very different characters, so that many new
genera have been formed. To Bruguiere, Lamark, and Dra-
parnaud, we owe all the improvements which have taken
place.

The modern genus BULL A includes those shells which cor-
respond with the following character : — " Testa univalvis,
convoluta, ovato-gibbosa vel cylindracea : spira non exserta,
apertura longitudine testae, labro acuto." The B. ampulla
is the type of the genus.

The genus O VUL.A, instituted by Bruguiere, is more nearly
related to the cyprea than to the bulla. It differs, however,
from the former, in the left margin of the lip being smooth ;
and from the latter, in the edges of the mouth being'rolled
inwards, and in the shell being produced at both ends. The
B. ovum of Linnaeus is the type of the genus; the B. patula
of Pennant.

" The bulla terebellum has been employed by Lamark to
constitute his genus TEREBELLUM. The canal at the base
of the mouth, and the truncated pillar, furnish the generic
characters.

Linnaeus was for some time uncertain where to place those
shells which he at last inserted in the genus bulla, under the
trivial names ficus and rapa. These, with a few of the mu-
rices of the same author, constitute the genus PYRULA of
Lamark. Its canaliculated base removes it from the bullae,
while the short spire, the swelling of the last whorl, thp
smooth pillar, and pyriform shape, distinguish it from all
those with which it is apt to be confounded. It is more
nearly allied to the Fusus than to any other.

The preceding genera consist of species which live in the
sea. The B. virginea is a terrestrial shell, and ought to

102 MOLLUSC A.

form a distinct genus next the bulinius. The B. fontinalis,
hypnorum, and rivalis, reside in fresh water. They have,
with much propriety, been formed into a distinct genus by
Draparnaud, which he calls PHYSA. They are all sinistral
shells, and will require further division when the form of the
animal shall become the basis of generic distinction. The
fontinalis and hypnorum are natives of Britain.

In the genus ACHATINA of Lamark, the pillar is trun-
cated as in the terrebellum, but the base of the mouth is
entire. It is represented by the bulla achatina of Linnseus.
To this genus we may refer theSuccinum acicula of Miiller,
which is found in England, and the Helix octona of Lin-
naeus, erroneously considered as a native of Britain.

22. VOLUTA. — This genus, as originally formed by Lin-
naeus, depended, as he informs us, on the plicae of the pillar,
" volutae genus facillime distinguitur columella piicata." But
as this character belongs to many shells otherwise very dif-
ferent in form, succeeding conchologists have separated
many species from the genus, and reduced it within more
natural limits. As it now stands it is thus denned, " Testa
univalvis, ovata, subventricosa, apice papillari ; basi emargi-
nata. Columella piicata ; plicis inferioribus, majoribus, vel
longioribus." The type of the genus is the voluta musica.

Bruguiere removed from the Linnaean genus those species
which are destitute of a groove at the base of their mouth,
and of which Lamark formed the genera AURICULA, TOK-
NATELLA, and VOLVARIA. In the latter the spire is not
produced ; in the former it is produced. To the genus au-
ricula, which contains land-shells, the V. auris-midce and
auris-judce belong. The V. tornatilis is the type of the
genus tornatella. In his reference to the genus volvaria,
Lamark quotes the bulla cylindracea of Pennant and Da

MOLLUSCA. 103

Costa, as if they were one and the same. But Pennant's
shell is a true bulla, while that of Da Costa is regarded as
the voluta pallida of Linnaeus, and probably belongs to this
genus.

In the genus OJLIVA, the turns of the spire are separated
externally by a very distinct gutter or canal, and the pillar
is obliquely striated. The valuta oliva of Linnaeus contains
many different species of this genus, which are remarkable
for the smoothness of their surface and the brilliancy of their
colours.

The ANCTLLA, which, like the former, is of a sub-cylin-
dric form, is destitute of the groove which separates the
whorls, and is characterised by an oblique callous ring at
the base of the pillar.

In the genus MITRA of Lamark, the spire is pointed in-
stead of ending in a small knob, as in voluta, and the plicae
of the pillar increase in size from the base upwards, which
is the re verse in that genus. The V. episcopalis of Linnaeus is
the type of this genus, which contains many species much
sought after by collectors,

In the COLUMBELLA, the shell is oval, the spire short,
and the inner edge of the right lip is swollen. The V.
mercaloria is the type of the genus.

Th.e MARGINELLA is very distinctly marked by the pro-
minent callous collar which surrounds the outside of the
right edge of the shell. The opening of the mouth at the
base is scarcely grooved. The V. glabella is the type of the
genus.

The CANCELLARIA is nearly related to the genus colum-
bella, but the absence of the swelling of the lip, and the
presence of the compressed sharp plicae of the pillar, furnish

104 MOLLUSC A.

sufficiently obvious characters of distinction. The V. can-
cellata of Linnseus is the type of the genus.

In the genus TURBINELLUS the shell is turbinated, sub-
fusiform, and canaliculated at the base, having from three
to five transverse compressed plicae on the pillar. The V.
pi/rum is the type of the genus.

23. BUCCINUM. — This is another of the Linnsean genera
of shells, which has undergone great alterations. As origi-
nally constructed, it embraced many distinct groups of shells,
which Bruguiere and Lamark have since formed into ge-
nera. The restricted character of the genus Buccinum is
thus defined by the last mentioned author : " Testa unival-
vis, ovata vel elongata. Apertura oblonga, basi emargina-
ta, nudata, canali nullo. Collumella convexa pi ana."

Bruguiere separated the genus CASSIS, in which the
opening is oblong and denticulated on the right side, with
a short canal towards the back of the shell. The right
margin has a callous border. The Buccinum cornutum of
Linnaeus is the type of the species.

The genus TEREBRA was likewise formed by the same
author. It is remarkable for its turreted form, the spire
being at least twice as long as the mouth, and the pillar at
the base twisted.

In the genus NASSA the groove in which the mouth ter-
minates is reflected as in Cassis, but the left edge of the
mouth is callous, and forms upon the pillar a transverse fold.

The PURPURA is readily distinguished from the Buccinum
and Murex, with which it has often been associated by its
naked compressed pillar, ending in a point at the- base.

The genus DOLIUM is distinguished by its bellied forms
and transverse rings, together with The margin on the right
side being denticulated its whole length.

MOLLUSC A. 105

The genus HARP A is well known, and is distinguished by
its sharp parallel longitudinal ribs. The pillar is smooth
and pointed at the base.

In the genus EBURNEA, the shell is smooth, and the pil-
lar umbilicated and subcanaliculated at the base. The
buccinum glabratum is the type of the genus.

24. STROMBUS. This Linnasan genus is now converted
into a family, distinguished by the right margin changing
its form with age, and having towards the base an inden-
ture or sinus. It contains four gerfera, strombus, rostel-
laria, pterocera, and hippocrenis.

In the genus STROMBUS, the canal is short, the right
margin is simple, and ends in a sinus. The S. pugilis of
Linnaeus is the type of this genus,

In the ROSTELLARIA the canal is produced into a long
beak, the right edge of the mouth is entire, and rests above
on the spire, and is sometimes decurrent. The sinus is con-
tiguous to the canal. The R. cornuta of Mart. (Conch, iv.
tab. 158. f. 1495,) is the type of the species.

In the PTEROCERA the canal is also lengthened, but the
right margin is dilated and digitated with a sinus near the
base. The strombus pes-pelicani of our shores is of this genus.

25. MUREX. The modern genus of this name is thus de-
fined by Lamark : " Testa univalvis, ovata vel oblonga ;
basi caniculata ; suturis varicose- tumudis, sub aspens, lon-
gitudinalibus, et persistentibus." In consequence of this
restriction, the following genera, among others, have bten
instituted.

In the genus FASCIOLARIA, the spires are destitute of
those longitudinal ribs which the murices always exhibit,
while the pillar is furnished with two or three oblique folds.
The murex tulipa of Linnaeus is the type of this genus*

106 MOLLUSCA.

The shell of the genus Fusus is lengthened, generally
fusiform, destitute of longitudinal ribs, and bellied in the
middle or lower part with a smooth pillar and lengthened
canal. The F. longicauda, (Lister, tab. 91 8, f. 1 1 . A.) is the
type.

The PLEUROTOMA is distinguished from the preceding
by a sinus or groove, which appears on the margin of the
right edge of the mouth, near its summit. It is represented
by the M. Babylonicus of Linnaeus.

The genus CLAVATULA differs from the former, in pos-
sessing a short canal, and ought never to have been separ-
ated.

In the genus CERITIIIUM, the mouth is oblique, termi-
nating below in a short truncated or recurved canal, and
having at the upper part a gutter more or less produced.
The Tympanotonos asper of Mart. (Conch. 4. p. 314. Tab.
156. f. 1473,) is the type of the genus.

26. TROCHUS. This is a very natural genus in the Lin-
naean system, and has undergone few alterations in the
hands of modern conchologists. The T. perspectivus has
given rise to a new and very obvious genus, termed SOLA-
RIUM, characterized by the internal spiral edge of the um-
bilicus being crenulated. Another species, the T. labio, is
the type of the genus MONODONTA, which contains shells
of an oval form, with a rounded mouth, furnished with a
tooth, formed by the truncated projecting base of the pil-
lar: the two margins are separated. The turreted trochi
of Linnaeus constitute the genus PYRAMIDELLA.

The T. terrestris of British writers is so imperfectly de-
scribed and figured, that it is impossible to assign it a place
in the system. It is nearly allied to the helix.

27 . TURBO. This very extensive genus has been greatly

MOLLUSCA. 107

dismembered by modern conchologists, in consequence of
Lamark having restricted the character in the following
terms : " Testa univalvis, conoidea vel subturrita. Aper-
tura integra rotundata, edentula ; marginibus superne sem-
per disjunctis; columella basi planulata." Our T. littoreus
is now considered as constituting the genus LITTORINA.

In the genus SCALARIA, the mouth is circular and bor*
dered, with the margins united. The spires are covered
with raised edged, slightly oblique, longitudinal ribs. The
famous wentletrap is the type of the genus.

Lamark thus defines his genus DELPHINULA : " Testa
univalvis subdisco'idea vel abreviato conica, solida, margari-
tacea, umbilicata ; anfractibus subasperis. Apertura rotun-
data, marginibus orbiculatim connexis." The T. delphinus
is the type of the genus. There are many species of tur-
bines common on our shores, which are excluded by the
preceding characters from the genera turbo and delphi-
nula, such as the striatus, cingellus, bryereus and others.
They are distinctly turreted, with the margins of the moutli
united, and constitute a genus termed CINGULA.

The Turbo terebra of Linnaeus serves as the type of an-
other genus, termed TURRITELLA, in which the margins of
the mouth are disjoined, the spire regularly turreted, and
the lip emarginated by a sinus. Nearly allied to the pre-
ceding is the genus PHASIANELLA, which Lamark thus de-
fines : " Testa univalvis, ovata vel conica, solida. Apertura
longitudiiialis, ovata, integra ; labro simplici acuto. Colu-
mella laevis basi attenuta. Operculum calcareum vel cor-
neum animali adherens."

Perhaps a rigorous examination of the turbines of British
writers might justify the formation of one or two new gene-
ra. In the genus ODOSTOMIA, the columella is furnished

108 MOLLUSC A.

with a tooth. The Turbo interstincta, unidentata, plicata,
Sandivicensis and insculpta of Montagu, are of this genus.
They have no resemblance in their structure to the Lin-
naean volutae ; although they have been inconsiderately as-
sociated with them by the authors of the Descriptive Cata-
logue. The preceding genera are formed of marine shells ;
those that follow live on the land.

In the genus CYCLOSTOMA, the mouth is circular, with
united, and often reflected margins. The animal is furnish-
ed with an operculum. The T. elegans of Montagu is the
only British species of the genus.

The species which are related to the Turbo bidens per-
versus and muscorum of Linnaeus, constitute a very natural
family, which may be termed PUPACEA, distinguished by
the mouth being furnished with teeth or testaceous lami-
nae, and the last whorl nearly the same or less than the pre-
ceding. Perhaps the most convenient way of dividing them
is into two sections, the first including the dextral, and the
second the sinistral shells.

The dextral pupacea form two genera. The PLTA, as
originally constructed by Lamark, was equally faulty with
many of the old Linnaean genera. As it has .been restrict-
ed to include dextral shells, with the animal possessing four
tentacula, with eyes at the tips of the two longest, it can
embrace the muscorum, sexdentatus, tridens, and juniperi
of Montagu. In the genus CAKYCHIUM, formed by Miil-
ler, the tentacula are only two in number, with the eyes
placed at the base. It is represented by the T. carychium
of Montagu.

The sinistral pupacea form likewise two genera. The
first, which is the Clausilia of Draparnaud, contains sinistral
shells, with the animal furnished with four tentacula, with

MOLLUSCA, 109

eyes at the tips of the two longest. This contains the fol-
lowing British species, viz. bidens, perversa, biplicata, plica -
tula, and labiata. The other genus, called VERTIGO, was
formed by Miiller. The animal possesses only two tenta-
eula, with the eyes on their tips. The T. vertigo is the
type of the genus.

28. HELIX. Linnaeus, in constructing this genus, at-
tended only to the character of the mouth being contract-
ed or lunated, without regarding the habits of the animals,
or even the other forms which the shells exhibited. Hence
he has united globose, discoid, and turreted, terrestrial, flu-
viatile, and aquatic shells ; animals with two and with four
tentacula, with and without an operculum, oviparous and
viviparous.

The marine species of Linnaeus are few in number. The
genus JANTHINA of Lamark, has been formed from the H.
janthina of Linn, a species of which has lately occurred at
several places of the Irish coast. The opening is triangu-
lar, and there is an angular sinus at the right edge. The
shell, which Linnaeus terms H. haliotoidea, is completely
concealed in the animal. There are many marine shells
inserted in the genus Helix by British writers, which either
belong to the restricted genus Turbo, or to the Vermicu-
laria.

The further reduction of the Linnaean helices depends
on the separation of the terrestrial from the fluviatile shells,
and subdividing these according to the characters furnUh-
ed by the different groups.

Among the terrestrial shells, the restricted genus HELIX
is by far the most extensive. It contains those shells which
are subglobose, with a convex spire ; the opening entire,
wider than long, and diminished in its upper part by the

1 10 MOLLUSCA.

projection of the last turn but one of the spire. The ani-
mal is furnished with four tentacula, with eyes at the tips
of the two longest. The H. pomatia is the type of the
genus.

The genus BULIMUS, as originally constructed by Bru-
guiere, was faulty in the extreme, but Lamark has new
modelled it so as to include those land shells which are tur-
reted or conical, with the mouth larger than broad, and hav-
ing, in general, the margin reflected with age. Like the
Helices, they have no operculum, and possess four subu-
lated tentacula.

From the Helix succinea of Miiller (the putris of Mon-
tagu and Donovan, not of Linnaeus) Draparnaud has form-
ed the genus SUCCINEA. The mouth is large in propor-
tion to the size of the shell, and effuse at the base with the
outer lip thin, and the pillar attenuated. The H. succinea,
although found in damp places, is not amphibious. It
never enters the water voluntarily. Indeed, Miiller says,
" Sponte in aquam descendere nunquam vidi, a contra quo-
ties eum aquae immisi, confestim egrediebatur." The same
remark is made by Montagu, and we have often witnessed
its truth.

The Helix pellucida of Miiller has been formed into a
new genus by Daudebard, which he termed Helico-limax,
but which Draparnaud, to avoid the use of a hybrid name,
changed for the term VITRIXA.

The fluviatile shells, included by Linnaeus in his genu&
Helix, may, for the sake of present convenience, be con-
sidered as forming two sections, viz. those with and those
without an operculum. To the former belongs the very
natural genus LIMNEA, containing conical or turreted shells,
with the right lip joined to the left at the base, and folding

JKOLLUSCA. Ill

back on the pillar. The H. stagnalis of Linnaeus, is the
type of the genus, of which we possess many British spe-
cies. Two of these are truly amphibious, the octona and
fbssaria.

The genus PLANORBIS, instituted by Geoffroy or rather
by Petiver, is remarkable for its discoid form, the spire re-
volving nearly in a horizontal line, so that all the whorls
are obvious on both sides. Cuvier observed that the P.
cornea was a sinistral shell, and it remains to be ascertained
whether the whorls in the other species have a similar di-
rection. We possess several British species of this genus.

The operculated divisions of fluviatile helices, is more
numerous than the preceding, containing at least six genera.

The genus VALVATA v/as instituted by Muller to include
depressed shells with an orbicular mouth, the animal, fur-
nished with three tentacula and a plumose appendage, con-
sidered as the branchiae. The V. cristata (Helix crist, of
Montagu), and piscinalis (the Turbo fontinalis of Montagu, )
are natives of this country.

The genus, now denominated PALUDINA, instituted by
Geoffroy, and afterwards employed by Montfort, is repre-
sented by the H. vivipara of Linnaeus. The shell is ovate
or oblong, with a regularly elevated rounded spire. The
aperture is entire, with the two lips united angularly at the
summit. The type of the genus, together with P. tentacit-
lata and acula, are natives of Britain.

In the genus AMPUIXAKIA of Lamark, the shell is glo-
bose, the base umbilicated, and the mouth longer than broad.
The H. ampullacea is the type of the genus.

In the genus HELICINA of Lamark, the mouth is semi-
lunar, the pillar callous and compressed below. The..//.

112 MOLLUSCA.

neritella, (Lister, Conch, tab. 61. fig. 59), is the representa-
tive of the genus.

In the genus MELANIA of Lamark, the shells are turret-
ed, longer than broad, effuse at the base, with a twisted
solid pillar. The H. amarula is the type.

The genus MELANOPSIS was instituted by Daudebard to
include the shells termed melanias by Olivier in his voyage
to the Levant. The mouth is lanceolate, the pillar trun-
cated and emarginated above with a callosity at the base.

29. NERITA. — This genus has been subdivided by Ad-
anson and Bruguiere into NERITA and NATICA. In the
former there is no umbilicus as in the N; exuvia, and, in the
latter, there is an umbilicus, as in the N.^anrena. Of the
restricted genus nerita, we possess two species; the littoralis,
common on our shores, and N. virginea. There are several spe-
cies of natica of British growth, the largest of which is the
glaucina. The fresh water species have been formed by
Lamark, with great propriety, into a distinct genus, under
the title Neritina. The N. jftuviatilis occurs in the English
rivers.

30. HALYOTIS. — This genus has been dismembered of
those species which are destitute of the perforations on the
disc. These have been formed into a new genus termed
STOMATIA.

31. PATELLA. — This genus, which at first sight appears
so very natural, contains shells which exhibit considerable
differences, both in form and structure, when narrowly ex-
amined. Geoffroy, with great propriety, separated the flu-
viatile species under the generic title ANCYLUS, a genus af-
terwards employed by Miiller. The animal is essentially
distinct from the marine patellae. There are two species

MOLLUSCA. 113

of this genus, the lacustris andftuviatilis, natives of Bri-
tain.

The genus PATELLA, as circumscribed by Lamark, has
been already sufficiently noticed. The common limpit may
serve as the type of this genus.

In the genus FISSURELLA, established by Bruguiere,
there is always an opening like a key-hole, near the summit
of the shell. The F. grceca and apertura are found on our
coasts.

The genus EMARGINULA is readily distinguished by the
slit or indentation which occurs on the posterior margin of
the shell.

In the genus CAPULUS of Montfort, the shell is conical,
with the summit produced into a beak, more or less recurv-
ed, and twisted. The P. hungarica of Lister is the type.
. The genus CONCHOLEPAS is furnished with an opercu-
lum, and in form and habits approaches the buccinum. It
is represented by the P. Integra of Da Costa's EL tab. 2.

fig. .7.

In the genus CREPIDULA, the cavity of the shell is par-
tially interrupted by a simple diaphragm. The P. parcel-
lana is the representative of this genus. The C. chinen-
sis inhabits the British seas.

In the preceding genus, the first approach to the turbi-
nated shell makes its appearance, which becomes more ob-
vious in the genus CALYPTR^A, in which the cavity is fur-
nished with a spiral diaphragm. The C. equestris is tht
type of the genus, which is related in part to the trochi.
From this genus of Lamark, Montfort has separated the IN-
FUNDIBULUM, as possessing a central spiral pillar. Sow-
erby has figured several species of this last genus in his

1 14 MOLLUSCA.

Mineral Concholoyy as occurring in a fossil state in Bri-
tain.

The patella unguis now ranks as a bivalve, and consti-
tutes the genus LINGULA in the acephalous family brachi-
opoda of Lamark. Linnaeus, who never saw more than one
valve, placed it among the patellae. Chemnitz, who ex-
amined both valves, considered it as a pinna. These writ-
ers had overlooked the figure of the perfect shell, with its
tube or stalk, as given by Seba, vol. iii. fig. 16. No. 4. This
specimen, which belonged to Seba, passed into the museum
of the Stadtholder, and afterwards reached, in company with
the spoils of the other Continental collections, the museum
of Paris. Here Lamark examined it, and formed his new
genus. And the same specimen enabled Cuvier to inves-
tigate its anatomical structure, which he has explained in
detail in the first volume of the Annales de Museum. Science,
in this instance, as well as several others, profited by the
successes of the late emperor of the French. This genus
is destitute of a hinge. The valves are supported on a pe-
duncle, and the shell is opened partly by the relaxation of
the adductor muscle of the animal (and not by the external
membrane, as stated by Mr. Sowerby), and partly by the
issuing forth of its spiral arms, which push asunder the
valves like a wedge.

Another genus was constituted and termed ORBICUL.A,
from the Patella anomala of Miiller, ZooL Dan. vol. i. p.
1 4. t. 5. The under valve is very thin, and fixed ; the up-
per is orbicular, and depressed. It is a member of the same
timiily as the preceding in the system of Lamark.

32. DENTALIUM. — This very natural genus of Linnaeus
has undergone no alterations, nor has our knowledge of the

MOLLUSC A, 115

inhabitant been satisfactorily enlarged. The Dentalium im-
perforatum, trachea, and glabrum of Montagu's Testacca
Britannica, do not accord with the essential character of
the Linncean genus in being "utraque extremitate pervia."

33. SERPULA. — This genus has undergone several changes
in the hands of modern conchologists. The S. seminulum
has been transferred to the genus miliola, and the S.filo-
granum to the tubipora. Besides these trivial alterations,
the character has been greatly circumscribed, so as only to
include shells which adhere to other bodies, and are tubu-
lar, entire and flexuous, with a simple mouth, as represent-
ed by the S. contortuplicata of Linnaeus. The species
which are regularly spiral, discoid, and fixed, as the S. spi-
rorbis, now constitute the genus SPIRORBIS. But as there
are both dextral and sinistral shells with this character,
the dextral species may form the genus Spirorbis, while
the HETERODISCA may receive the reversed species.

The genus VERMICULARIA is formed from those species
which, in appearance, resemble the spirorbis, but are not
adherent, such as the S. lumbricalis. The shell at the
mouth is, in general, somewhat produced. There are two
or three minute British shells of this genus.

The genus SILIQUARIA, represented by the S. anguina,
is distinguished from the serpula by a longitudinal, lateral,
subarticulated fissure, which extends the whole length of
the shell.

The genus PENICILLUS is formed from that curious shell
the S. penis, and well known by the name of the watering-
pot. The disk is perforated by a number of small holes.

34. TEREDO. — From this genus, now considered as a bi-
valve (the tube being regarded as an accessory covering),
the FISTULANA, of which T. clava of Gmelin is the

116 MOLLUSCA .

sentative, has been separated. The external tube in this
genus is closed at the posterior extremity, while in teredo
it is open. The S. polythalamia forms, according to La-
mark, the genus SEPT ARIA, and the two genera XYLOPH A -
GA and CLAVAGELLA have more recently been instituted.
35. SABELLA. This last genus of the Linnaean vermes
testacea has been degraded from its rank in conchology.
The covering consists of agglutinated particles of sand and
fragments of shells, and bears no resemblance to the testa-
ceous coverings of the true mollusca. It is now placed in
company with the terebella, and the three preceding Lin-
naean genera among the ANNELIDES.

In the preceding brief review of the Linnaean genera of
shells, the reader will probably have been astonished at
those changes which have taken place. In this country we
are so much accustomed to the artificial method both in
zoology and botany, that we often reject, without sufficient
consideration, the improvements which the study of the natu-
ral method has suggested. In the time of Linnaeus, per-
haps, the genera of the shells, with a few exceptions, were
sufficiently numerous and commodious to embrace all the
known species ; but since the science has been cultivated
with more zeal, in consequence, we must say, of the intro-
duction of the natural method, the number of species has
increased tenfold. New genera and orders, and other
conventional divisions, have been formed, suited to the
state of improvement of the science. The merit of all
these improvements did not originate with Bruguiere or
Lamark, whose names we have so often had occasion to
mention. Many of the modern genera may be traced to the
systems which prevailed before the days of Linnaeus ; sys-

MOLIAJSCA. 117

terns which the Swedish naturalist, in his desire to simpli-
fy, when simplicity was impracticable, too incautiously dis-
regarded.

1 1 8 MOIXUSCA.

CHAPTER III.

SYSTEMATICAL DISTRIBUTION OF TKE MOLLUSCA.

THE successful methodical disposition of molluscous ani-
mals, could not have been accomplished previous to labours
similar to those of Cuvier and Lamark ; or until the shell
and the contained animal were studied as connected objects.
When thus contemplated, molluscous animals admit of ar-
rangement into two great classes, or divisions, which may
be distinguished from each other by well-defined characters*
In the one, the presence of a head may be recognised, to-
gether with eyes, and even ears in some of the groups. In
the other, containing animals much less perfect in their or-
ganization, there is no head, neither vestige of eyes or ears
in any of the species. The former have been termed Mot-
lusca Cephala, the latter Mollusca Acephala. This ar-
rangement was first employed by Baron Cuvier, and after-
wards by Lamark and other modern systematical writers.
In the last work of the former naturalist, this method is de-
parted from, and the six classes to which we have already
referred, are constituted of equal rank, instead of being
placed in subordination to the two primary divisions under
which they can be suitably distributed.

MOHLUSCA. 1 1 9

DIVISION I. MOLLUSCA CEPHALA.

Head distinct from the body, bearing the lips or jaws.

The head, or the anterior part of the body on which
Zoologists have bestowed that denomination, possesses more
or less freedom of motion, and, on the dorsal aspect, sup-
ports either tentacula or eyes, frequently both. The ani-
mals of this division exhibit so many modifications of form
and structure, in all the series of organs, that the positive
characters which they possess in common are few in num-
ber. They easily admit, therefore, of subdivision into in-
ferior groups which exhibit well-marked characters of dis-
tinction. Two of these groups occupy a primary rank, and
admit of the others being included under them as subordi-
nate sections. In the first of these, the animals are all in-
habitants of the water, and perform their progressive mo-
tion through that element by organs fitted for swimming.
They are destitute of any ventral disc on which to crawl.
In the second group, including animals which inhabit the
land, as well as those which live in fresh water and in the
sea, progressive motion is performed by means of crawling
along the surface of objects, the body resting on a ventral
disc termed a foot.

SECT. I. — NATANTIA. — Organs of progressive motion
fitted for swimming*.

The organs of motion are situate near the anterior ex-
tremity of the body, and consist either of flexible tentacula
or membranaceous expansions. All the species reside in
the sea. They are nearly of the same specific gravity with

120 MOLLUSCA.

the surrounding fluid in which they float about, having their
motions in a great measure regulated by its changes. It is,
however, probable, that, by means of some Contractile
movements, they are capable of varying their density, and
of rising or sinking in the water. They swim slowly, even
with their utmost efforts. The animals of this section be-
long to the classes which Cuvier has termed Cephalopoda
and Pteropoda.

CLASS I. — CEPHALOPODA.

Fins in the form of -tentacula, surrounding the mouth.

The Cephalopoda, in reference to their external appear-
ance, may be regarded as consisting of two parts ; the tunic
or sac, which contains the viscera, and the head, surround-
ed by the tentacula. The skin is usually mottled with
minute coloured spots, the colour varying in in tensity in differ-
ent spots, and even in different parts of the same spots. These
are confined to a thin layer on the outer surface of the true
skin. In a living state these spots change their colour in
rapid succession as if a coloured fluid was expelled from
them or replaced in variable quantity. The sac is, in some
species, in the form of a purse, destitute of any appendages,
while in others, it exhibits fin-like expansions. It varies
considerably in its consistence : in some, it is strengthened
on the back internally, by corneous ribs or testaceous plates,
and in others, it is protected externally by spiral shells. In
some species, it is connected with the head by an interven-
ing space, which may be regarded as a neck, but in others,
the tunic and head are continuous behind. In all, it ex-
hibits, after death, great changes of colour.

On the summit of the head there is a flattened disc, in

MOLLUSCA. 121

the centre of which is seated the mouth. Round the mar-
gin of this oral disc, which is strengthened by a band of
muscular fibres, are placed the arms or tentacula. Beyond
this circle of arms, in some species, there are situated two
organs, larger in their dimensions than the arms, which may
be denominated feet. Both the arms and feet are covered
on their central aspect with numerous suckers, by which
they are enabled to attach themselves to different bodies,
and to seize their prey ; and in their axis, both a nerve and
artery may be observed. These arms and feet are capable
of being moved, at the will of the animal, in every direc-
tion, and are the organs by which progressive motion is per-
formed. In the space between the head and tunic in front,
there is an opening or funnel with a projecting aperture.
This funnel opens into the cavity of the sac, and serves
both to convey water to the gills, and to carry off the differ-
ent excreted matters.

The brain in the Cephalopoda is contained in an irregu-
lar hollow ring, in the cartilaginous border of the oral disk.
This cartilage is thickest on the dorsal aspect, and contains
the parts which have been denominated cerebrum and cere-
bellum, the remaining part of the canal being occupied with
the collar, which surrounds the esophagus. The nerves,
which proceed directly from the brain to the parts which
they are destined to influence, are few in number. From
the cerebrum a few small nerves issue, which go to the
mouth, and the base of the feet, while some proceed U,
form ganglia at the mouth, and others supply the feet. The
cerebellum, besides furnishing the collar which encircles
the gullet, contributes to the formation of the large ganglia
which supply the arms, the optic and auditory nerves,
those for the funnel, the tunic, and the viscera. From the

122 MOLLUSCA.

size of the animals, the ganglia of the nerves are very dis-
tinctly displayed. The anastomosing branches of the nerves
of the arms are likewise conspicuous. Each nerve, at the
base of each arm, sends out two filaments, one to the nerve
of the arm on each side. In this manner a chain of nerves
is formed round the base of the arm, probably calculated to
enable them to act more readily in concert. From the
abundant distribution of nerves to the different parts, it ap-
pears probable that the sense of touch exists in a tolerably
perfect manner. There is no proof of the development of
organs for the display of the senses of smell and taste.

The Cephalopoda are furnished with two eyes, one on
each side of the head. The external membrane on the
inner side, which may be compared to the sclerotica, differs
in many particulars from the covering of the same name in
the eyes of the vertebral animals. While it surrounds the
contents of the eye from the entrance of the optic nerve to
the pupil, it is greatly separated from the choroides. Im-
mediately within its cavity, there is a bag, with a peculiar
membranaceous covering, which contains numerous glan-
dular bodies, similar to the milt of fishes, by which the eye
is supported, and which probably act as secreting organs
(although M. Cuvier could not detect any excretory canals),
and likewise an expansion or ganglion of the optic nerve.
The concave or anterior surface embraces the choroides.
This membrane, after enclosing the vitreous humour, forms
a zone or diaphragm, which may be compared to the ciliary
processes, with an aperture in the centre for the reception
of the crystalline lens. The circular margin of this aperture
is lodgedina circular groove of the lens, andintimately united
with it, so that the lens is divided into two unequal hemis-
pheres. Its central surface is coated, as in the higher

MOLJLUSCA. 123

classes of animals, with the coloured mucous pigment which
has been denominated pigmentum nigrum. In the cepha-
lopoda, however, it is of a purplish-red colour.

The optic nerve, after entering the sclerotica, expands
into a large ganglion, from the peripheral surface of which,
issue numerous nervous filaments. These pierce the cho-
roides by as many holes, and go to form, by their reunion,
the retina. This important membrane extends to the cili-
ary zone, and, like it, appears to unite itself with the groove
of the lens.

The vitreous humour is contained in a peculiar vesicle,
having the lens seated in a concavity on its external sur-
face. The lens divides easily into two parts, the line of
separation being the groove which receives the ciliary liga-
ment. The separated surfaces are flat, and the outer por-
tion is in the form of a planoconvex lens. Each portion
consists of a number of concentric layers of variable thick-
ness, composed of radiated fibres, becoming less and less
distinct towards the centre, near which the laminated and
radiated appearances cease to be perceptible. An imper-
fect representation of this structure is given by Sir E. Home,
probably from preparations by Mr. John Hunter, in the
Phil. Trans, vol. Ixxxiv. tab. 5. p. 26.

The conjunctiva supplies the place of a cornea, and covers
directly the crystalline lens, as there is no aqueous humour.
This membrane, in some, is continuous with the skin, but
in others, there are imperfect eye-lids formed by its dupli-
cature, previous to passing over the lens. The skin, at the
opening of the pupil, formed by the sclerotica, in the ab-
sence of an uvea and iris, is strengthened by a membrane
which appears to be muscular, and probably assists in the
contraction or enlargement of the aperture.

124 MOLLUSC A.

The animals of the cephalopodous class, besides contain-
ing complicated eyes, are likewise furnished with ears. These
are situate in the annular cartilage which supports the arms.
In this cartilage, there are two cavities, in each of which
there is a bag filled with a gelatinous, transparent fluid, and
containing a calcareous substance, differing in its consis-
tence according to the species, from the brittleness of starch
to the hardness of bone. The auditory nerve penetrates
the walls of this labyrinth, and ramifies on the membran-
ous bag which it contains. There is no external opening,
nor any apparent alteration in the thickness of the invest-
ing integuments.

The digestive system of the Cephalopoda exhibits seve-
ral appearances by which it may be distinguished. The
arms which surround the mouth, seize the animals which
are to serve as food, and bring them to the mouth. The
mouth is situated in the centre of the disc, round which the
tentacula are arranged. It is surrounded with a slight fold
of the skin, which may be compared to lips, and which is
rough on the central aspect. Within the lips are the two
mandibles, of a deep brown colour, hard, horny consistence,
and in form resembling the beak of a parrot. Where free,
they are conico-tubular, but where covered, they are open
at the central side. The under beak, unlike the same
organ in birds, is the largest, the most crooked, and em-
braces the upper, or the one on the dorsal margin of the
mouth. These jaws are merely able to open and shut, as
they possess no lateral motion. They are supported by the
muscular bed of the mouth, which serves as a mould to fill
the cavity towards the point. The tongue is situate be-
tween the beaks, and is armed with reflected teeth. These
teeth, in consequence of the undulatory motion of the sub-

MOLLUSC A. 125

stance of the tongue, expedite the progress of the food into
the gullet.

The salivary glands are four in number, and are placed in
pairs. The glands of the first pair, seated on each side of the
muscular bed of the mouth, are divided into numerous lobes,
the excretory ducts of which pour their fluid into the beginning
of the gullet. The second pair, seated lower down and be-
low the eyes, are not so much divided, and send out separ-
ate canals, which unite and pour their contents into the
mouth.

The gullet is furnished with a lateral expansion, not un-
like the crop of gallinaceous birds. The stomach is mus-
cular, like the gizzard of fowls, and the cuticle is thick, and
separates easily from the other membranes. At the pyloric
opening of the stomach, there is another aperture equally
large, which leads into the spiral stomach, or caecum, as it
has been improperly termed by some anatomists. It may
with greater propriety be denominated the duodenum, as it
performs some of the offices of that part of the gut in the
higher orders of animals. This stomach is conical, closed
at the distal extremity, and performs about a turn and a
half, like a spiral shelL Its inner surface is covered with a
ridge, which traverses it in a closely spiral direction. The
bile flows into it near the apex, and towards its base glan-
dular orifices, pouring out a thick, yellow fluid, may be ob-
served. The intestine, after leaving the pylorus, in some
species, makes one or two turns, in others, it proceeds di-
rectly to the anus. This opening is seated at the base of
the funnel, on its posterior or dorsal side.

The liver is of considerable size, of an orange-yellow co-
lour, and of a soft and spongy texture. It gives rise to two

1 26 MOLLUSCA.

hepatic ducts, which proceed to the extremity of the spiral
stomach, where, by a common orifice, they empty the
orange-coloured bile which they contain.

The organs of circulation consist merely of veins and ar-
teries. The veins which have their origin in the feet, mouth,
and annular cartilage, coalesce, and form two branches,
which afterwards unite into a common trunk. This vessel,
after descending through part of the viscera into the abdo-
men, divides into two branches, each of which may be con-
sidered as a vena cava, conveying the blood to the lateral
hearts. Each vena cava, at its origin, is joined by an equal-
ly large vessel, which empties its contents in a direction
nearly at right angles with the former. These veins arise
in the stomach, intestines, liver, and organs of generation.
The vena cava receives a second large vessel, nearly in the
same direction as the first, which has its origin in the tunic
and the supports of the branchiae. From the size of the
vena cava, in consequence of the union of these two branches,
and the appearance of muscular ridges on its inner surface,
it has been compared by some to an auricle.

On each side, in the common cavity of the tunic, and
near the gills, an aperture may be observed, the entrance
to a bag or cavity. Each cavity is traversed by the vena
cava of that side, and in its passage exhibits a curious con-
formation. The surface of the vein is covered with spongy,
glandular bodies of different shapes. These, upon being
pressed, pour out an opake, yellow, mucous fluid. Within,
these glands communicate by very wide ducts with the ca-
vity of the vein. Indeed, when air is blown into the vein,
it readily passes through the glands into the bag, and thence
into the cavity of the tunic ; and when air is blown into

MOLLUSCA. 127

the bag, it likewise penetrates the gland, and passes into
the veins. The arteries with which these glands are fur-
nished are comparatively minute.

It appears probable that these glands separate some prin-
ciple from the blood, and that this is conveyed away by the
ejection of the water from these venous bags into the com-
mon cavity. Were it practicable to analyse the yellow
mucus which these glands contain, some light might be
thrown on the subject. Indeed, it appears not improbable,
that this arrangement is analogous in its functions to the
urinary system in the most perfect classes.

Each vena cava enters its corresponding lateral heart or
ventricle, through an intervening valve. Each lateral heart
is situate at the base of each gill, is pear-shaped, black, and
moderately thick, with numerous pits on its inner surface.
Its narrow end terminates without any valvular structure
in the pulmonary artery. In the genus octopus, the lateral
hearts are naked ; but in the genera Loligo and Sepia, there
is suspended from each, by a slender footstalk, a spongy
round body, which is concave beneath. The footstalk con-
sists of fibres, which are attached to the surface of the heart,
but there is no communication by ducts or vessels. The
use of this organ is unknown.

The animals of this class continually reside in the water,
and respire by means of gills or branchiae. These are
double, one on each side, corresponding with the lateral
pulmonic ventricles. Each gill is connected at its opposite
sides to the tunic, by means of fleshy ligamentous bands.
Between these, the double leaves of the gills are arranged
in an alternate series. Each leaf is supported by a foot-
stalk from the band, and is subdivided into smaller leaves,
to expose a greater surface to the water.

128 MOLLUSC A.

The pulmonary artery passes along this band, sends a
branch into each footstalk, which, penetrating the substance
of the gills, conveys the blood to its different divisions.

The systemic veins depart from the gills at the opposite
extremity. These unite at the inferior band, and from each
gill a vessel proceeds to the single central or systemic heart
or ventricle. In some of the animals of this class the sys-
temic veins are somewhat enlarged, and assume the appear-
ance of auricles. The two pulmonary, or rather the sys-
temic veins, enter the heart at the opposite side, each at the
termination being furnished with a valvular organization.

The systemic heart is white and fleshy, and differs ac-
cording to the genera, in its form, being in the Octopus se-
micircular, but in the Loligo and Sepia lobed. Besides
giving rise to a large aorta, Qr principal artery, two smaller
ones likewise proceed from its cavity. These arteries are
furnished at their entrance with valves.

The sexes in the Cephalopoda are distinct, the male and
female organs being found on different individuals. There
is not, however, any external mark by which they may be
distinguished. M. Cuvier found that the males of the Oc-
topus were scarcely a fiftn part so numerous as the females.

The male organs of generation consist of the following
parts : The testicle is a large white glandular purse, con-
taining numerous fringed filaments, from which the seminal
fluid is secreted. This fluid passes out of the testicle by a
valvular opening, into the vas defer ens. This canal is slen-
der, and greatly twisted in its course, and opens into a ca-
vity which has been compared to the seminal vesicle. The
walls of this last cavity are strong and muscular, and dis-
posed in ridges. Near the opening at the distal extremity
of this sac is an aperture leading into an oblong glandular

MOLLUSCA. 129

body, regarded as exercising the functions of a prostate
gland. Beyond this lies a muscular sac, divided at the top,
where it opens by two ducts, but connected at the base. In
this sac are numerous white thread-like bodies, terminated
by a filament, but unconnected with the sac. In the in-
terior they consist of a spiral body, connected at each ex-
tremity with a glandular substance. When these bodies
are put into water, they twist themselves in various direc-
tions, and throw out at one of their extremities an opake
fluid. These motions are not excited by placing them in
oil or spirit of wine, but they may be exhibited by immers-
ing in water those which have been kept for years in spirits.

These bodies, first observed by Swammerdam, and after-
wards by Needham, have been regarded by some as de-
monstrating the truth of the vermicular theory of genera-
tion ; by others, they have been considered as analogous to
the pollen of plants, their tunic is in part soluble in water,
and when they are thrown into that fluid, they speed-
ily burst, and spread their impregnating contents over the
eggs of the female. Although this last conjecture is plau-
sible, and countenanced by the circumstance that these ver-
micular bodies are only found at the season of reproduction,
the subject is still involved in obscurity. Are these bodies
produced in the testicle, and only brought to this bag when
nearly ready for exclusion ; or, if the product of the bag
itself, by what means are they nourished ?

The male organs terminate in a cylindrical fleshy body
termed the Penis. This is hollow within, and ribbed with
muscular bands. Near its base it receives one of the ducts
of the vermicular sac, continuous with the one from the pros-
tate gland, forming its canal, and toward the apex the other
duct. It projects but a short way into the cavity of the

1 30 MOLLUSCA.

great bag, into which it empties its contents. These pass
out of the body at the funnel-form opening in the throat.

The female organs of generation consist of an ovarium
and oviduct. The ovarium is a glandular sac, to which the
ova are attached by footstalks. The opening by which they
issue from the ovarium is wide, and the oviduct (in the Oc-
topus vulgaris and Loligo sagittata,) after continuing a
short way simple, divides into two branches, each having
its external aperture near the anus. The oviducts are fur-
nished within with muscular bands and a mucous lining, and
encircled with a large glandular zone, destined, probably,
to secrete the integuments of the eggs. In the Loliga vul-
garis, and the Sepia, the oviduct continues single. Be-
sides these organs, the Loliga vulgaris and sagittata, and
the Sepia, have two large ov#l glandular bodies, divided by
transverse partitions, with their excretory ducts terminating
at the anus, the use of which is unknown. The eggs, of
the peculiar form already noticed, pass out of the funnel,
after which they are supposed to be impregnated by the
male, according to the manner of fishes.
- The inky fluid now remains to be considered, as the most
remarkable of the productions of this tribe of animals. The
organ in which this 0uid is secreted is spongy and glandu-
lar. In some species it is contained in a recess of the liver,
which has given rise to the opinion, that the coloured fluid
which it secreted was bile. In other species, however, this
gland is. detached from the liver, and either situate in front
or beneath that organ. The excretory canal of this gland
opens in the rectum, so that the fluid escapes through the
•funnel. It mixes readily with water, and imparts to it its
own peculiar colour. When dried, it is used as a pigment,
and is considered as the basis of China ink. It is regarded

MOLLUSCA. 131

by Signior Bezio as a peculiar substance which he has de-
nominated Melaina. It is obtained by digesting the ink
with very dilute nitric acid, until it become yellowish, wash-
ing it well, and separating it by the filter ; it is then to be
frequently boiled in water, one of the washings to be a lit-
tle alkalized ; and, finally, with distilled water. The me-
laina is a tasteless, black powder, insoluble in alcohol, ether,
and water, whilst cold, but soluble in hot water ; the solu-
tion is black. Caustic alkalis form with it a solution even
in the cold, from which the mineral acids precipitate it un-
changed. It contains much azote. It dissolves and de-
composes sulphuric acid. It easily kindles in the flame of
a candle. It has been found to succeed as a pigment in
some respects, better than China ink. (Dub. Phil. Trans.
Nov. 1825.)

The Cephalopoda are all inhabitants of the sea. They
are widely distributed, occurring in the arctic as well as the
equatorial seas. In the latter, however, they grow to the
largest size. It is reported, that in the Indian seas, boats
have been sunk by these animals affixing to them their long
arms, and that they are dreaded by divers.

The two Linnaean genera, Nautilus and Sepia, compre-
hend all the animals which are at present considered as be-
longing to this class.

ORDER I. — NAUTILACEA.

Furnished with a multilocular shell.

This order is involved in the greatest obscurity. None
of the recent species have been subjected to an accurate
examination, so that their connection with the order Sepia-
cea may still be considered doubtful. Enough is known of

132 MOLLUSCA.

the animals of two of the genera, to furnish some hints for
those who are fond of classifying animals from their analo-
gies. These genera are SPIRULA and NAUTELUS.

In the Spirula, the shell, which is concealed under the
skin of the back, is spiral, with the whorls separate, the
mouth orbicular, the chambers perforated by a pipe, and
the last cell produced into a tube. The position and use
of this terminal tube are unknown. The S. vulgaris is the
most common species, and inhabits the seas in the West
Indies. In the restricted genus Nautilus, the shell is sup-
posed to be external, and the body of the animal to be lodg-
ed in the last chamber, and to be fixed by a ligament which
descends into the central pipe. In the shell itself, the turns
of the spire are contiguous, and the last whorl embraces the
others on the sides. The N. P-ompilus of RUMPHIUS is the
only species in which the animal has been detected.

The other genera which have been formed in this order
depend exclusively on the characters furnished by the shells ;
and the resemblance which these bear to the preceding
genera, constitutes all their claim to be included in the pre-
sent order.

ORDER II. — SEPIACEA*

Destitute of a multilocular shell.

The sac is strengthened by horny or testaceous plates,
unless where the habits of the animal render such support
unnecessary.

1. Head surrounded with eight arms and two feet.

The two feet are nearly similar in their structure to the
arms, or tentacula, but considerably larger in their dimen-

MOLLUSCA, 133

sions. They have their origin on the ventral side of the
mouth, between that organ and the funnel. The suckers
are pedunculated, with their margin strengthened by a corn-
eous ring, furnished with teeth. The sac is furnished with
fin-like expansions, and strengthened internally by corneous
or testaceous ribs or plates. The head is divided from the
sac on all sides by a neck. The margin of the anus is sur-
rounded with tentacula.

GENUS SEPIA. The sac is furnished on each side through-
out its whole length with a narrow fin.

The suckers are irregularly scattered on the arms and
feet. The back is strengthened by a complicated calca-
reous plate, lodged in a peculiar cavity. This plate has
been long known in the shop of the apothecary under the
name Cuttle-fish bone, which was formerly much prized in
medicine as an absorbent, but is now chiefly sought after
for the purpose of polishing the softer metals. It is some-
what ovate, flatly convex on both sides, and thickest where
broadest. The superior half, or the one next the head, is
the longest, rounded at the extremity, and thin. The in-
ferior portion becomes suddenly narrow, and ends in a point.
It may be considered as consisting of a dermal plate, con-
cave on the central aspect, having uits concavity filled up
with layers which are convex on their central aspect.

According to our observations, the dermal plate appears
to consist of three different laminae, arranged parallel to one
another. The external or dorsal layer is rough on the sur-
face, and marked by obscure, concentric arches towards
the summit, formed by minute knobs, which become larger
towards the base, where they appear in the form of inter-
rupted transverse ridges. It is uniform in its structure, and
the tubercles possess a polish and hardness equal to porcel-

134 MOLLUSC A.

laneous shells, although they blacken speedily when put
in the fire, and contain a good deal of animal matter. On the
central side of this layer there is one flexible and transpa-
rent, similar to horn, and smooth on the surface. The third
layer is destitute of lustre ; and, in hardness and structure,
resembles mother-of-pearl shells.

The layers which fill the concavity of this dermal plate
are slightly convex on the central aspect, and are in part
imbricated. Each layer is attached to the concave surface
of the dermal plate, by the upper extremity and the two
sides, while the inferior or caudal extremity is free. The
inferior and first formed layers are short, occupy the base
and middle, and rise from the plate under a more obtuse
angle than the new formed layers, which are both the long-
est and the broadest.

Each layer, which is about one-fiftieth of an inch in dia-
meter consists of a very thin plate, the dermal surface of
which, when viewed with a magnifier, exhibits numerous
brain-like gyrations. From the ventral surface of this plate
arise numerous perpendicular laminae, which, when viewed
laterally, appear like fine parallel threads, but when examin-
ed vertically, are found to be waved, and fold upon them-
selves. Next the plate they are thin, and not much fold-
ed ; but towards their other extremity they become thicker,
striated across, and more folded, with irregular margins.
On the thick, tortuous even ends of these lamina?, the suc-
ceeding plate rests, and derives from them the peculiar
markings of its surface. These laminae are closely set, ir-
regularly interrupted, and occasionally anastomose. M.
Cuvier states, erroneously, (Mem. sur la Seiche, p. 47.)
that these laminae are hollow pillars disposed in a quincunx
order.

MOLLUSCAc, 135

The term bone has been improperly applied to this com-
plicated plate ; " for," according to Mr. Hatchett, (Phil.
Trans, vol. Ixxxix. p. 321.) " this substance, in composition,
is exactly similar to shell, and consists of various mem-
branes, hardened by carbonate of lime, without the small-
est mixture of phosphate."

The most remarkable species of this genus is the Sepia
officinalis, which is distinguished from the others by its
smooth skin. It inhabits the British seas, and although
seldom taken, its bone is cast ashore on different parts of
the coast, from the south of England to the Zetland isles.

GENUS LOLIGO. Calamary. Sides of the sac only fur-
nished partially with fins.

The suckers are disposed on the arms and feet in a
double row. The dorsal plate is flexible and corneous, im-
bedded in the substance of the sac, and is multiplied with
years. Dr. Leach has described three new species of the
genus Loligo, which were collected by Mr. Cranch during
the voyage to the Congo, in that unfortunate expedition
under the direction of Captain Tuckey. These species be-
long to a group which have the suckers produced into hook-
ed processes. In two of these species, L. leptura and
Smithii, the suckers on the arms, as well as the feet, are
produced into hooks, while, in one species, L. Banksii, the
feet only are armed with hooks.^

The same distinguished naturalist has instituted a new
genus nearly allied to Loligo, from two species collected
during the same voyage. The following characters are as-
signed to it.

" GENUS CRANCHIA. — Body oval, sac-shaped ; fins ap-
proximating, their extremities free; neck with a frenum

136 MOLLUSCA.

behind, connecting it with the sac, and with two other
frena, connecting it with the sac before.

"Sp. 1. Cranchia scabra. — Sac rough, with hard, rough
tubercles.

" Sp. 2. Cranchia maculata. — Sac smooth, beautifully
mottled with distant ovate spots." (Narrative of an Ex-
pedition to explore the river Zaire, usually called the
Congo in South Africa, in 1816, under the direction of
Captain J. K. Tuckey, R. N. London, 1818, p. 410.)

Head surrounded with Eight Arms without Feet.

The suckers have soft margins. The sac is destitute of
fin-like expansions, and is either simple or strengthened in
the interior by two short corneous processes. The head is
united with the sac behind, without the intervention of n
neck.

a. Arms all equal in Size.

GENUS OCTOPUS. — Suckers arranged in a double row.

The suckers are sessile. The oviduct is double. The
margin of the anus is simple. The Sepia octopodia of Lin.
is the type of the genus.

GENUS ELEDONA. — Suckers on the arms disposed in a
single row.

M. Lamark has figured and described two species of this
genus, in the Mem. de la Soc. (THist. Nat. One of these is
a native of the Mediterranean, and is remarkable for giving
out an odour like musk.

b. Arms unequal.

GENUS OCYTHOE. — Two of the arms at their inner ex-
tremities furnished with membranaceous expansions.

In this genus, which was instituted by M. Rafinesque,
the suckers are in a double row, and supported on foot-

MOLLUSC A. 137

stalks. In the specimens of the Ocythoe Cranchii, pro-
cured during the expedition to the Congo, Dr. Leach ob-
served " four oblong spots on the inside of the tube, re-
sembling the surfaces for the secretion of mucus, two in-
ferior and lateral, and two superior, larger, and meeting an-
teriorly. On the rim of the sac, immediately above the
branchiae, on each side, is a small, short, fleshy tubercle,
which fits into an excavation on the opposite side of the
sac." (Phil. Trans. 1817.)

This animal was long considered as the fabricator of the
shell termed Argonauta or Paper Nautilus. The observa-
tions of Mr. Cranch, the zoologist to the Congo expedition,
were supposed to have demonstrated that the shell is merely
the temporary residence of this animal, which it quits at
pleasure. The body of the animal does not conform in
shape to the cavity of the shell, nor to all its irregularities
of surface ; neither is there any muscular attachment be-
tween them. " On the thirteenth of June," (says Dr. Leach,
when publishing the notes of Mr. Cranch,) " he placed two
living specimens in a vessel of sea-water ; the animals very
soon protruded their arms, and swam on and below the sur-
face, having all the actions . of the common Polypus (oc-
topus) of our seas ; by means of their suckers, they adhered
firmly to any substance with which they came in contact,
.and when sticking to the sides of the basin, the shell might
easily be withdrawn from the animal. They had the power
of completely withdrawing within the shell, and of leaving
it entirely. One individual quitted its shell and lived seve-
ral hours swimming about, and showed no inclination to re-
turn into it ; and others left the shells as he was taking them
up in the net. They changed colour, like other animals of
the class Cephalopoda ; when at rest, the colour was pale

138 MOLLUSC A.

flesh-coloured, more or less speckled with purplish ; the
under parts of the arms were bluish-grey ; the suckers whit-
ish." The specimens which furnished an opportunity for
making the preceding observations, were met with in the
Gulph of Guinea, and afterwards on the voyage, swimming
in a small argonauta, on the surface of the sea. The reader,
who is desirous of farther information on this subject, may
consult Dr. Leach's Observations on the Genus Ocythoe of
Rafinesque, Sir E. Home on the Distinguishing Characters
between the Ova of the Sepia, and those of the Vermes Tes-
tacea that live in water, in the Philosophical Transactions
for 1817, art. xxii. and xxiii., (both of which are added to
the appendix of Captain Tuckey's Narrative,) and a paper
by Mr. Say, on the genus Ocythoe, in the Phil. Trans.
1819? art. vii. More recently, however, naturalists seem
disposed to reunite the Ocythoe with the Argonauta, though
the question cannot be considered as determined.

CLASS II. — PTEROPODA.

Fins formed of membranaceous expansions.

This class was instituted by Cuvier, for the reception of
a few genera, the peculiar characters of which indicated the
impropriety of suffering them to remain in any of those
categories which had been previously established. All
the species are small in size ; and the attempts hitherto
made to investigate their internal structure, have, in a great
measure, failed in explaining the functions of the organs
which are exhibited. The valuable papers of Cuvier, on
the Clio, Pneumodermon and Hyalea, include nearly all the
accurate information on the subject, of which naturalist-
are in possession.

MOLLTJSCA. 139

The general form of these animals is somewhat ovate.
The tunic appears in some genera, as the Clio and Pneumo-
dermon, to be double, the external one soft and thin, the
internal exhibiting a fibrous structure, corresponding to the
muscular web of the skin of the higher classes. In these
animals, however, the two layers are unconnected through-
out the greater part of their expansion. In some, as the
Cymbullia, the tunic is cartilaginous, while in others it is
strengthened by a shell. In these last, the shell in the Li-
macina is a spiral univalve, covering the abdominal viscera,
and in the Hyalea, where it serves the same purpose, it ap-
proaches in character a bivalve shell. It is, however, des-
titute of a hinge, the two valves being united together at
their caudal margins, and there is no appearance of a trans-
verse adductor muscle.

The organs of motion in all the genera consist of two fins,
or membranaceous expansions, one being seated on each
side of the head. They have no foot wherewith to crawl,
nor any suckers by which they can adhere to objects. They
are, therefore, free animals moving about in the water by
means of their fins, and probably possessing, at the same
time, a power of varying their specific gravity, as they are
capable of varying, to a certain extent, the form of their
bodies, and of enlarging or reducing their dimensions. There
is nothing peculiar in their nervous system.

The organs of digestion differ greatly from those of the
Cephalopoda, which we have already considered. They are
generally regarded as destitute of eyes and ears. Their
tentacula are either seated on the head, forming two com-
plicated branches of filaments, or spread along the margin
of the tunic. There are no arms for seizing the food. The
mouth, however, is furnished with lips ; and in some there is

140 MOLLUSCA.

an appearance of a tongue at the entrance of the gullet. The
salivary glands are two in number, lengthened, descending
a considerable way into the abdomen, and pouring their
contents, by means of their excretory canals, into the cavity
of the mouth. The gullet, after being encircled by the ner-
vous collar, suffers an enlargement, which has been termed
a crop, contiguous to which is the stomach. Both these
cavities exhibit muscular ridges on the inner surface. The
liver surrounds the stomach, is intimately united with its
contents, and pours in its bile by numerous pores. The in-
testine is short, and, after making one or two turns, ascends
and terminates in the neck near the mouth.

The circulating system in this class has been but very
imperfectly investigated. The pulmonic vessels are un-
known, but systemic veins, a single auricle, ventricle, and
aorta, have been detected. The heart, in some, is situate
on the left, in others, on the right, side of the body.

The aerating organs exhibit very remarkable differences.
In the Clio they are in the form of a fine net- work on the
surface of the fins ; in the Pneumodermon they are conjec-
tured to form leafrlike ridges on the caudal extremity of the
body ; or if these ridges are to be considered as particular
kinds of fins, the gills may be sought for on the membrana-
ceous expansions of the neck. In the Hyalea the branchiae
form a complex band on each side of thejbody, at the lateral
opening of the shell.

The animals of this class are all hermaphrodites. There
is a common cavity, a vesicle, penis, vas deferens, and tes-
ticle, together with an oviduct and ovarium. These open
near the mouth on its ventral margin. There is nothing
known with respect to the appearance of the eggs, the pe-
riod of propagating, or the form of their young.

MOLLUSCA. 141

All the animals of this class inhabit the sea. Some, as the
Clio and Limacina, frequent the arctic regions, and afford
the whale a great part of its sustenance. None of the spe-
cies have hitherto been detected in the British seas.

M. Cuvier divides the animals of this class into cephalous
and acephalous. In the latter division he places the genus
hyalea. The head of the animal of this genus, with its in-
ferior neck, may, however, be sufficiently recognised to re-
move all doubt of its existence.

The characters which may be employed in the classifica-
tion of this group are numerous ; but the influence which
their different forms exercise on the habits of the species is
still unknown. The following disposition of the genera,
though it has no claims to a natural division, may be useful
to the student in his investigations.

(1.) Tunic Strengthened by a Shell.

GENUS LIMACINA. — Posterior extremity of the body co-
vered by a spiral shell.

The shell, which is very tender, makes one turn and a
half, is flat on one side, with a large pillar cavity on the
other. The fins are two in number, one on each side of the
neck. When the animal swims, the head with the fins are
protruded.

This genus was instituted by Cuvier, for the reception of
the Clio helicina of Captain Phipps, or Argonauta arctica
of Fabricius. According to Mr. Scoresby, it is found in
great quantities near the coast of Spitzbergen.

GENUS HYALEA. — Posterior extremity of the body pro-
tected by two connected shelly valves.

In the animals of this genus, the body is lodged between
two plates or valves, united at the base, where they inclose
the caudal extremity. The ventral valve is nearly flat, with

142 MOLLL'SCA.

an uneven margin, narrow anteriorly, but expanding behind,
and terminating in three projecting points. From the mid-
dle point four ribs diverge forward, and a muscle arises,
which, fixed in the superior viscera, enables the animal to
withdraw into the shell. The dorsal valve is shorter than
the preceding, the margin flat and circular, and the middle
convex outwardly. The branchiae are situate in the space
between the lateral margin of the two valves, on each side,
in a duplicature of the tunic, the sides of which are furnished
with filaments. The fleshy neck supports the two mem-
branaceous expansions ; between which and the base the
mouth is situate, surrounded by two lips, and strengthened
within by two fleshy cheeks. The opening of the anus and
oviduct are at the base of the right fin.

The Hyalea tridentata, the best known species of the
genus, was first noticed by Forskal, in his Descriptions Ani-
malium, p. 124, as an Anomia, and inhabiting the Mediter-
ranean. The same species was likewise taken in abundance
in the Gulf of Guinea, by the expedition under Captain
Tuckey.

(2.) Tunic destitute of a Shell.

A. Fins double.

Posterior extremity with leaf-ltike ridges.

GENUS PNEUMODERMON* — Head with two bundles of ten-
tacula.

The body is oval, with a narrow neck, and a fin on each
side. The mouth is nearly terminal, furnished on each side
with a fleshy lip, and beneath, with a fleshy chin. Each
tentaculum consists of a filament, with a tubercle at the end,
pierced by a small hole, and considered as exercising the
office of a sucker. Cuvier, in his Memoire sur FHyale et
le Pneumoderme, considered the leaf-like ridges which oc-

MOLLUSC A. 143

cur on the caudal extremity of the body, as the branchiae,
and even describes the pulmonary vein which conveys the
blood from these to the heart. But, in his Regne Animal,
he states it as the opinion of M. Blainville, that the fin-like
expansions of the neck contain the branchiae on their sur-
face, as in the case of Clio. The rectum and oviduct ter-
minate under the right wing. Cuvier has figured and de-
scribed the only known species, which he terms Pneumo-
dermon Peronii, the trivial name being in honour of the
discoverer, M. Peron.

Posterior extremity simple.

GENUS CLIO — Body ovate, with the tunic elongated and
membranaceous.

The head is divided into two lobes, the summits of which
are furnished with tentacula. The existence of eyes has
not been ascertained. The mouth is transverse, with two
lateral longitudinal lips. On each side of the neck arise two
blunt, conical, fin-like expansions, with a fine reticulated
surface, considered as serving the double purpose of fins
and branchiae. The anus and orifice of generation termi-
nate under the base of the right branchia. The viscera do
not fill entirely the cavity of the inner bag. The gut makes
only one fold.

The genus Clio was originally instituted by Brown in
his Natural History of Jamaica. It was afterwards em-
braced and modified by Linnaeus and Pallas, in such a man-
ner as ultimately to exclude the species for the reception of
which Brown originally formed it. It contains two species,
the most remarkable of which is the Clio borealis. Mr.
Scoresby, in his valuable work on the Arctic Regions, states,
(vol. i. p. 544), that it occurs in vast numbers in some situ-
ations near Spitzbergen, but is not found generally through-

144 MOLLUSCA.

out the arctic seas. In swimming, it brings the tips of the
fins almost into contact, first on one side and then on the
other.

GENUS CLEODORA. — Body covered with a triangular py-
ramidal tunic.

The fins are membranaceous. The mouth is situate be-
tween these, and is furnished with a semicircular lip. This
genus was instituted by Peron, for the reception of the Clio
of Brown. The C.pyramidata is the best ascertained spe-
cies. Brown's Jamaica, p. 386, tab. 43, f. 1. Two other
species were taken by the Congo expedition, in S. lat. 2. 14.,
and E. long. 9- 55., and S. lat. 2.41., E.long. 9. 16., "both
having a spinous process on each side of their shell, near its
opening. One species is beautifully sulcated transversely,
and the other but slightly so." — Tuckey's Narrative, p. 412.

B. Fin single.

GENUS CYMBULIA — Tunic cartilaginous and trough-
shaped.

The fin is single, divided into three lobes, one of which
is small, with two tubercles, and a minute fleshy beard.
This genus was instituted by Peron, in Annales du Museum,
t. xv. t. 3, f. 10, 11.

SECT. II. — GASTEROPODA. — Organs of Progressive Mo-
tion fated for Creeping.

This is one of the most extensive groups of molluscous
animals. The marks by which it is distinguished are well
defined, and the external and internal characters of the spe-
cies have been successfully illustrated.

The Gasteropoda may be considered as having the body
protected dorsally by the cloak, and ventrally by the foot.

MOLLUSCA. 145

The cloak is either continuous, and usually more or less
arched, for the reception of the viscera underneath, or it is
interrupted by a projecting bag, in which are contained the
principal digestive and reproductive organs. This project-
ing bag is tapering and spiral, and always protected exter-
nally by a shell. When the cloak is continuous, the surface
is variously marked, and frequently exhibits a particular
portion more elevated than the rest, in some cases conceal-
ing a testaceous plate, which has been termed the shield.

The foot situate on the ventral aspect, and in opposition
to the cloak, exhibits a flat, soft surface, consisting of inter-
laced muscular fibres. Its central surface serves as a sup-
port to the viscera, while externally it constitutes the organ
of progressive motion. It is a sucker rather than a foot,
and enables the animal to adhere to objects when at rest,
and to crawl from one place to another by a succession of
adhesions, not unlike the leech. It is also used as a fin in
swimming.

By the union of the cloak and foot laterally and posteri-
orly, a sac is formed, which is open in front for the protrusion
of the neck and head. The line of junction between the
cloak and foot is marked, in general, by peculiarities in the
condition of the margins of both.

The neck is usually divided from the cloak by a collar, or
thickened margin belonging to the cloak, or rather to the
shield;, while in other cases it is continuous. Underneath,
the neck is frequently attached to the foot.

The head supports the tentacula and eyes, is free dor-
sally, but frequently intimately connected with the foot on
its ventral side. The portion between the tentacula and
the mouth is termed the snout, (le mufle of the French, and
its margin le chaperon). The mouth exhibits various mo-

146 ! MOLLUSCA.

difications of.fleshy lips and corneous jaws. The inside oi
the cheeks are covered in some species with reflected teeth,
to aid deglutition. The tongue can scarcely be detected in
some of the genera; while, in others, it is a simple tubercle,
or a strap-shaped, spiral organ, armed with transverse rows
of teeth. This spiral tongue, where it is fixed to the base
of the mouth, is broadest, and there also the spinous pro-
cesses are strongest. The spiral part is narrowest and soft-
est, and folded up behind the pharynx. M. Cuvier conjec-
tures, and apparently with plausibility, that the spiral portion
comes forward into the mouth to act as a tongue, in propor-
tion as the anterior part is worn by use and absorbed. (See
his Memoir e sur la Vivipare tfeau douce, p. 12; and Mem.
sur laPatelle, p. 17).

The organs of respiration exhibit the two modifications
of lungs and gills, to enable us to divide the Gasteropoda
into two classes, which we have termed Pulmonifera and
Branchifera. M. Cuvier appears to have been in some mea-
sure aware of the importance of the distinction, when he
instituted his order Pulmones; but he afterwards suffered
himself to be more influenced by the presence of an oper-
culum, the shape of the aperture of the shell, and the sup-
posed separation of the sexes, than by the characters of the
respiratory organs. '

Some shells are simply tubular or conical ; but the greater
part are variously convoluted, the volutions being termed
whorls or spires. These whorls are in general visible and
distinct, the boundary between each being termed the line
of separation. The whorls in some species are simply placed
in a lateral position, while in others the whorls are formed
upon a pillar, or columella, which runs in the direction of
.the axis of the shell, the inferior whorl in this case embrac-

MOLLUSCA. 147

ing the superior one. The pillar is in some cases nearly
solid, in other instances tubular, with its base either open
or covered. When the base of the tube of the columella is
uncovered, the opening is termed the pillar cavity, or um-
bilicus.

In general, when a spiral shell is placed upon its base or
mouth, with the apex towards the observer, the mouth will
be found situated on the right side, and the whorls will be
observed revolving in a direction from right to left, or cor-
responding with the motion of the sun. These shells are
termed dextraL A few species have this order reversed, as
the observer will readily perceive. For upon placing the
shell in the above-mentioned position, the mouth will be
found situated on the left side, and the whorls will revolve
from left to right. These shells are termed sinistral, hete-
rostrophe, or heteroclite.

CLASS I PULMONIFEBA.

The pulmonary cavity is single and lateral. Its orifice is
capable of being closed at the will of the animal. The
bloodvessels are spread, chiefly on the walls and roof, like
delicate net-work. The opening of the cavity is usually on
the right side, with the anus behind it, and the sexual ori-
fice is in the front near the head. In some of the genera,
these openings are situate on the left side. The shells of
the former are denominated dextral, of the latter sinistral.
This change in the position of the external openings is ac-
companied by a corresponding alteration in the arrangement
of the internal organs* The heart, for example, is always
placed on the side opposite the pulmonary cavity. In the
dextral shells, therefore, it is sinistral. In both kinds, how-

148 MOLLUSCA.

ever, all the organs preserve the same relation to the back
and belly, the head and tail. It is impossible, therefore, to
conceive a dextral animal changed into a sinistral, by any
circumstance which could take place at the period of hatch-
ing, as M. Bosc was inclined to believe. This arrangement
of the organs must have been not merely congenital, but
coeval with the formation of the embryo. In some species
all the individuals are sinistral, while in others the occur-
rence is rarely met with in a solitary example. The former
are in their natural state, the latter ought to be regarded as
monsters. Where the character is permanent, it should
constitute a generical difference.

The reproductive system of the animals of this class ex-
hibits the sexual organs, in general, united in the same in-
dividual. Mutual impregnation, however, is necessary. All
the species are oviparous. The eggs are either naked, as
in the terrestrial genera, or enveloped in a gelatinous mass,
like the aquatic kinds. The embryo acquires nearly all its
members while in the egg, and the shell is of a proportional
size previous to hatching. Sir Everard Home, when treat-
ing of the distinguished characters between the ova of the
sepia, and those of the vermes testacea that live in water,
(Phil. Trans~> 1817, p. 297), and when referring to the ova
of the vermes testacea, says, " If the shell were formed in
the ovum, the process of aerating the blood must be very
materially interfered with, for this reason, the covering or
shell of the egg, first drops off, and the young is hatched
before the shell of the animal is formed ; this I have seen
take place in the eggs of the garden snail, but in the tes-
tacea that live in water, the young requires some defence in
the period between the egg being hatched and the young
acquiring its shell, which is not necessary in those that live

MOLLUSC A. 149

on land ; for this purpose the ova are enclosed in chambers
of a particular kind." The assertion here made, and found-
ed on a priori considerations, that the shell is not formed
until after the egg is hatched, is opposed by every observa-
tion which we have been able to make on the subject; and
what is more surprising, it is at variance with his own ob-
servations on the garden snail, the very example produced
in its confirmation. The eggs of a snail, laid on the 5th of
August 1773, were hatched on the 20th of that month,
and their condition at this time distinctly stated. "On the
20th," he says, "the young were hatched, and the shell
completely formed/' It is much more becoming in a phi-
losopher to observe how nature operates, than to pronounce
what she must do-

ORDER I — TERRESTRIAL.

The animals of this order reside constantly on the land.
When by accident they fall into the water, they appear to
be incapable of using their foot as a sucker or as a fin, and
die after a few writhings. The species in general prefer
moist places, and are seldom very active in dry weather.
After a shower they speedily leave their hiding places, and
at this time they may be readily collected. The eggs are
hatched on land,

1st Subdivision.

Cloak and foot parallel, and containing the viscera between
them.

In this group are included those animals denominated
slugs in this country. They possess four retractile tenta*
cula, of unequal length, though in some cases one pair is

150 MOLLUSCA.

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 cartilagino'us 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 caecum 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 venae cavse, which
give out numerous branches to the pulmonary cavity. The
aerated 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 rruscu-
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.

MOLLUSCA. 151

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.

GENUS ARION. — A mucous orifice at the termination of
the cloak.

This genus was instituted by M. le Baron D'Audebard de
Ferussac, in his Histoire Naturelle Generale et Particuli-
ere des Moftusques 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 Limax ater (together with its variety rufus)
of British writers may be regarded as the type of the genus.
The genus PI^ECTROPHORUS, distinguished by a conical
protuberant shell at the termination of the cloak, was like-
wise instituted by M. Ferussac, and nearly resembles the
preceding in form. Three species have been described

152 MOLLUSCA.

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. Ferussac, 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 appears as 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 PARMACELLA. — 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 TESTACEULA. — Tail 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.

MOLLUSC A. 153

The foot extends on each side beyond the body. From the
manner in which the blood is aerated, the auricle and ven-
tricle are placed longitudinally, the latter being anterior.

GENUS ONCHIDIUM — 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 Lin. Trans., vol. v. p. 132, for the
reception of a species which he found in Bengal, on the
leaves of Typha Eiephantina. 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 anus and 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
SNAILS. 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 i«,
{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.

154 MOLLUSC A.

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 CYCLOSTOMA. — 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
mouth is formed into a kind of proboscis, and the upper lip
is deeply emarginate.

GENUS HELIX 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

MOLLUSC A. 155

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 subservient to any other purpose, can scarcely
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 bidens per-
versus and muscorum of Linnaeus, constitute a very natural
family, which may be termed PUPAD^, distinguished by the
mouth being, in general, furnished with teeth, or testaceous
laminae, 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 VITRLNA. — 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.

GENUS SUCCINEA. — Termination of the pillar rounder!.
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 Dtaparnaud and named SUC-
CINEA. Afterwards Lamark proposed the term Amphibu-
lina, but latterly adopted that of Draparnaud. The name first
employed indicates one of the most striking characters of the

156 MOLLUSCA.

type of the genus; whereas thetermAmphibulina,is founded
on a mistake, and is apt to mislead. The Helix #uccinea,
(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 aquae immisi, confestim egredie-
batur." The same remark is made by Montagu, and we
have often witnessed its truth.

ORDER 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, is deposited on aquatic
plants under water. Previous to hatching, the foetus must
be aerated by means of some branchial arrangement.

GENUS LIMNEA. — 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

MOLLUSCA. 157

the pulmonary cavity. In consequence of this arrangement,
the individuals of L. stagnates have been observed by Geof-
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 quote his own words :
" L'animal est pourvu de quatre filamens ou tubes qui par-
tent de la partie superieure du cou, pres du manteau ; ce sont
destraehees. Ces tubes sont longs, blancs et tres transparens,
et on ne les distingue bien qu' a la loupe. Leur surface est
comme rugueuse, et leur extremite est un peu renflee. Us
sont retractiles. L'animal les fait sortir a volonte, 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 presume que par ce movement ces organ es sepa-
rent de 1'eau 1'air que y'est contenu et 1'absorbent. Get
animal est tres sujet, ainsi que les autres gasteropodes flu-
viatiles, a etre infeste par le nais 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

158 MOLLUSCA.

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 L.
auricularia possesses, like those which it resembles in other
characters, a pulmonary cavity.

GENUS PHYSA. — Pillar-lip destitute of a fold, and the
whorls are sinistral. (Zool.Journ. vii. 363.) The external ap-
pearance of the animal is similar to the Limnea; but the mar-
gin of the cloak is loose, divided into lobes, and capable of
being reflected over the surface of the shell near the mouth.
This genus was instituted by Draparnaud. The Bullafonti-
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 Butta 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 PLANORBIS. — Cavity of the shell entire. This is
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, between the foot
and the margin of the cloak.

GENUS SEGMENTINA — 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
triradiated apertures. It is uncertain whether the animal
is to be considered as dextral or sinistral. This genus was
instituted by us several years ago, for the reception of the
Nautilus lacustrisof Lightfoot, first described and figured ia
Phil. Trans, vol. Ixxvi. p. 160. tab. 1. f. 1, 8.

MOLLUSCA. 159

GENUS PERONIA. — The body is destitute of the external
protection of a shell. The head is furnished with two long
retractile tentacula. The snout is divided into two broad ap-
pendages. Between the tentacula, towards the right side, is
the opening for the penis. The anus is terminal, immediately
above which is the entrance to the pulmonary cavity ; and on
the right is the opening to the female organs, from which a
groove runs towards the right lobe of the snout. The mouth
is destitute of a proboscis or jaws. The tongue is merely
a cartilaginous plate grooved transversely. The gullet is
long in proportion, with a villous surface. There are three
stomachs, each distinguished by its peculiar characters.
The first is a true gizzard, covered internally with a carti-
laginous cuticle, and its walls formed of two strong muscles,
with connecting ligaments. The second stomach is funnel-
shaped, with prominent ridges both on its external and internal
surface. These ridges, at their origin internally, are high-
est, and project considerably into the cavity, acting like a
valve in retarding the progress of the food. The third
stomach is short and cylindrical, covered internally with
equal longitudinal fine ridges. The intestine is nearly of
equal thickness throughout, and upwards of twice the length
of the body. The salivary glands are much branched, and
pour their contents into the entrance of the gullet. The
liver, in the animals of this genus, is distributed into three
separate portions, each of which may be regarded as a dif-
tinct liver, an arrangement which is not known to take place
in any other animal. The first liver is situate near the mid-
dle of the body, on the right side ; while the second is
placed near the posterior extremity. The ducts enter the
cardiac opening of the stomach, each by a separate aperture,
and seem to occupy the place of the zone of gastric glands

160 MOLLUSC A.

observed in birds. The third liver is placed at the posteri-
or end of the gizzard, into which it pours its contents by a
short duct.

The most remarkable feature of the circulating system,
is the position of the lungs at the posterior extremity of the
body, which occasions a corresponding arrangement in the
connecting organs. The entrance to the pulmonary cavity
is immediately above the anus. The vessels in which the
blood is aerated, are distributed on the roof and sides of
the cavity. The pulmonic veins consist of two receptacles,
one on each side, extending nearly the length of the body,
which may considered as venae cavae. These receive the
blood by numerous vessels, and convey it directly to the
lungs. The aerated blood is conveyed by a systemic vein
into a large auricle, seated in'front of the lungs, of consider-
able size, with the walls fortified on the interior by branch-
ed ligaments. The ventricle is placed at its anterior ex-
tremity, and separated by two valves. The aorta arises
from the opposite side of the ventricle, its main trunk pass-
ing on towards the head.

The male and female organs of generation, although oc-
curring in the same individual, appear to occupy different
parts of the body. The opening of the male organs is at
the tentacula, which leads to a cavity terminating in two
unequal recesses. The anterior is the smallest, and receives
the termination of a vessel three or four times longer than
the body, which takes its rise at the external base of the
cavity, apparently from the cellular substance, and, after a
variety of convolutions in the neighbourhood of the mouth,
opens into the recess. The second recess is the largest, and
the vessel connected with it is most complicated. Its ori-
gin is in a mass which occupies a considerable portion of the

MOLLUSC A. 161

abdominal cavity, and which consists of a vessel forming a
great number of complicated convolutions, liberally suppli-
ed with bloodvessels. The duct proceeds from this mass,
undergoes for a short space a sudden thickening of its walls,
after which it again contracts, and, before it terminates in a
perforated glandular knob in the recess, it contains a pe-
dunculated fleshy body, with a sharp-pointed corneous ex-
tremity, probably capable of being protruded into the recess
and cavity. The parts which are considered as forming the
female organs, or those which are connected with the sexu-
al cavity on the right side of the anus, consist of an ovari-
um, divided into two lobes, each of which may be perceived
to be again minutely subdivided. The oviduct is tortuous,
and passes through a glandular body, which, in the other
gasteropoda, is regarded as the testicle. The pedunculated
vesicle gives out two ducts, one of which goes to the testi-
cle, the other to the uterus. It is difficult to form even a
conjecture regarding the uses of all this complicated sexual
apparatus. The subject can only be elucidated by an at-
tentive examination of the condition of the organs at differ-
ent seasons of the year, and by studying, at the same time,
the habits of the animals.

The preceding description of the characters of the genus
is taken from the anatomical details of a species found
creeping upon the rocks under water in the Mauritius, by
M. Peron, which Cuvier referred to the genus Onchidiun*
of Buchanan, already noticed. We have ventured to insti-
tute the genus, and to name it in honour of the discoverer
of the first ascertained species. Cuvier conjectures that it
breathes free air, and has accordingly inserted it among the
pulmones aquatique. Some doubts, however, may reason-
ably be entertained as to the truth of this supposition. It

162

MOLLUSCA

would certainly be an unexpected occurrence, to find a mar-
ine gasteropodous mollusca obliged to come to the surface,
at intervals, to respire. It will probably be found that it is
truly branchiferous.

CLASS II! — BRANCHIFERA.

The molluscous animals of this class are more numerous
than those of the preceding. They chiefly inhabit the wa-
ters of the ocean, a few genera only being met with in fresh
water lakes and rivers. The branchiae which constitute their
aerating organs, exhibit numerous varieties of form, posi-
tion, and protection, and furnish valuable characters for their
methodical distribution.

ORDER I — BRANCHIAE EXTERNAL,.

The branchiae are pedunculated, and more or less plu-
mose. They are moveable at the will of the animal, and,
in general, are capable of great alteration of form.

GENUS DORIS. — Oral tentacula two ; vent without scales.
The cloak is covered with retractile papillae, and separated
from the foot by a distinct duplicature. Towards its ante-
rior margin are placed the two superior tentacula. These
are retractile, surrounded at the base with a short sheath,
and supported on a slender stem, having an enlarged com-
pound plicated summit. The neck is short, and above the
mouth there is a small projecting membrane, connected at
each side with the oral tentacula, which are in general mi-
nute, and of difficult detection. The mouth is in the form
of a short trunk, leading to 'fleshy lips, within which the
tongue is placed. This last organ is covered with minute

MOLLUSCA. 1 63

reflected hairs, and, from its motion, appears to be destined
exclusively for deglutition. The gullet is a simple mem-
branaceous tube, terminating in a stomach, which presents on
the interior a few longitudinal folds. It is furnished with a
small caecum, the extremity of which receives the bile from
the liver. The stomach likewise receives the secretion of
another gland, which is not connected with the liver, in the
form of a small bag, the inner surface of which is covered
with numerous papillae. The intestine is lodged in a groove
on the surface of the liver, and proceeds directly to the
anus. The liver itself is divided into two lobes, and gives
rise to numerous biliary ducts, which proceed to the sto-
mach. But it likewise gives rise to a duct which proceeds
to a small bag plaited on the inside, and afterwards opens
on the surface at a small hole near the anus. It yet remains
to be determined, whether the fluid carried off by this con-
duit be excrementitious matter, separated by the liver, or
whether the gland which produces it be distinct from that
organ? but so interwoven therewith as to elude the obser-
vation of the anatomist.

It is obvious, from the structure of the digestive organs,
that the species subsist on soft food, requiring neither cut-
ting nor grinding, and in this respect, differ remarkably
from the species of the genus Tritonia, which were formerly
arranged along with them.

The organs of generation differ little from the other her
maphrodite gasteropoda. The vesicle furnishes two canals,
one of which goes to the testicle, the other to the penis.
There is likewise a minute bag connected with the canal of
the latter. The spawn is deposited on sea-weeds and stones.
It is gelatinous, of a white colour, and in appearance resem-
bles the sponge denominated Grantia compressa.

164 MOLLUSC A.

GENUS TRITOXIA. — Branchiae destitute of basilar sheaths.
The branchiae are in the form of plumes, or imbricated pro-
ductions, placed in a row on each side the back. The ten-
tacula, which are partially retractile, have a sheath at the
base. In some of the species there are indications of eyes.
The mouth consists of two lips, which are placed longitudi-
nally, and open into a short canal. The jaws consist of two
corneous plates, united at the upper dorsal edge, slightly
arched, and meeting at their upper margin, for the purpose
of cutting. Within these is the tongue, which differs re-
markably from the same member in the doris. In the lat-
ter, the spines with which it is beset are reflected, and draw
the food to the gullet, while in the former, the spines are
deflected, and serve to keep the food within the reach of
the jaws. The tongue of the doris, therefore, serves for
deglutition, that of the tritonia for mastication. M. Cuvier
describes the functions of both as similar. The salivary
glands are placed on each side the gullet, and empty their
contents behind the jaws. The gullet has a few longitudi-
nal folds ; the stomach is simple, scarcely differing from the
gullet ; and the intestine proceeds almost directly to the
anus, situate on the right side. The liver is small, and situ-
ate behind, enveloping the stomach, and intimately united
with the ovarium. The organs of generation exhibit no-
thing remarkable. The pedunculated vesicle has a simple
canal. The external opening of the organs of generation
is situate a little before and beneath the anus. The T.
Hombergii arborescens, pinnati/ida, and bifida, are exam-
ples of British species.

GENUS SCYLLEA. — Branchiae seated dorsally on the fins.
Tentacula two. On each side of the back are two mem-
branaceous expansions, and one on the tail, supporting on

MOLLTJSCA. 165

their dorsal surface scattered plumose branchiae. Each of
the tentacula is furnished with a large funnel-shaped sheath.
The foot is very narrow, with a mesial groove, used in
climbing up the stalks of sea- weeds. The mouth is placed
at the base of the tentacula, and surrounded with a semi-
circular lip. The tongue is in the form of a tubercle, with
reflected points. The gullet is plaited longitudinally. The
stomach is short and cylindrical, with a ring of hard, longi-
tudinal scales. The liver consists of six unequal globules,
and the bile is poured into the cardiac extremity of the gul-
let. The Scyllea pelagica has been long known to naturalists,
and appears to be very common in the equatorial seas, ad-^
hering to the stems of the Fucus natans.

GENUS THETHYS. — Branchiae forming a row on each side
of the back, consisting of fringed processes, alternately larg-
er and smaller. The body is ovate, with the cloak and foot
continuous. The neck is distinct from the foot, and is nar-
row. Above, the neck is continuous with the cloak, from
which arises a large semicircular expansion, used probably
as a fin. The margin of this expansion is fringed with nu-
merous filaments, and on the upper surface, within the
border, is a row of conical tubercles. The true tentacula
are placed towards the base of this fin near the neck. Each
of them consists of a small fleshy cone, striated across, with
a semicircular sheath behind. The branchiae consist of a
tapering, fleshy stalk, spirally twisted towards the summit
with a series of filaments on one side. They are fourteen in
number on each side,alternately and oppositely small and large.
The anus opens in front of the third branchia on the right
side. The orifice of generation is exhibited under the first
branchia of the same side. In front of each of the larger
branchiae, is a small cavity with a .small filament in the cen-

166 MOLLUSCA.

tre. The mouth is situate underneath the tentacula. It
consists of a large funnel, covered within with soft papillae,
destitute of jaws or tongue. The gullet is short, the sto-
mach simple, fleshy, and covered with a thick cuticle. The
salivary glands are slender and branched, and open into the
gullet. The intestine is likewise short, and proceeds di-
rectly to the anus. The liver pours the bile into the canal
at the pylorus ; and likewise sends out another duct, which
opens externally near the anus. The organs of generation
are similar to the Doris. The T.fimbria is the type of the
genus, a figure of which, with its anatomical details, is given
by M. Cuvier, in his Memoire sur le Genre Thetys.

GENUS VALVATA. — In this genus are included several
species which resemble in aspect the aquatic pulmoniferous
gasteropoda. The branchiae appear in the form of a fea-
ther, with a central stem, and a row of compound branches
on each side, decreasing in size from the base to the free
extremity. This stem issues from the neck near the middle,
a short way behind the anterior tentacula. Near this plume,
but towards the right side, is a single simple filament, like
a tentaculum. The anterior tentacula occupy the usual
position, are setaceous, and have the eyes placed at the base
behind. The spiral shell is capable of containing the body,
and the aperture can be closed by a spirally striated oper-
culum attached to the foot. The internal structure is un-
known.

GENUS PATELLA — Shell entire. Mouth with tentacula.
This genus differs from the others of the order to which it
belongs. The back is covered by a conical shell, within
the cavity of which the animal is capable of withdrawing
itself. The cloak is large, covering both the head and foot.
It is united with the shell along its superior margin. The

MOLLUSC A , 167

foot is fleshy, and furnished with numerous muscular fila-
ments, which unite, in the superior part of the cloak, to
form a strong muscle, by which the body adheres to the
shell. The action of this muscle brings the shell close to
the surface to which the foot adheres, or removes it to a
distance. The head is furnished with a large, fleshy snout,
supporting at the base two pointed tentacula. The eyes
are placed on a small elevation at the external base of the
tentacula. A little way behind the head, and below the
cloak, on the right side, are two apertures, being the anus
and orifice of generation. The gills occupy the same po-
sition as in the preceding genera. In some, the branchiae
form a complete circle ; in others, the circle is interrupted
anteriorly at the head.

Within the trunk, the mouth is fortified by two cartila-
ginous cheeks, which, at their union anteriorly, support the
base of the tongue. This last is a most singular organ. It
is longer than the whole body, narrow, and covered with
three rows of short reflected spines, interrupted longitudin-
ally and transversely. Its fixed end only can be exercised
in deglutition, its free end being coiled up the abdomen.
On the upper side of the mouth is a semicircular osseous
plate, or upper jaw. The gullet is furnished with a dilat-
able pharynx. The stomach is elliptical, with the cardia
and pylorus at opposite extremities. The intestines are
variously folded, and are several times longer than the body.
The salivary glands are minute. The liver is intimately
united with the stomach and intestines. The heart is situ-
ate on the left side, in the anterior part of the body. The
auricle receives the aerated blood from one vein when the
circle of the gills is complete, and by two when interrupted.
This auricle is placed on the anterior side of the heart. An

168 MOLLUSC A.

aorta arises from each side, to convey the blood to the body-
The ovarium is placed underneath the liver ; and, as it ex-
hibits some differences of organization, M. Cuvier infers
that it likewise contains the male organs. The species be-
longing to this genus are numerous, and appear to admit of
distribution into sections ; the first having the branchial
circle complete, the second interrupted.

GENUS CHITON. — Shell constituting a series of imbri-
cated dorsal plates. The body is elliptical. The cloak
is firm and cartilaginous, and variously marked on the mar-
gin. The dorsal plates are arched, and occupy the middle
and sides of the back, where they are implanted in the
cloak, in an imbricated manner, the posterior margin of the
first valve covering the anterior margin of the second. The
foot is narrow. The mouth is surrounded with a semicir-
cular curled membrane, and is destitute of tentacula. The
anus consists of a short tube, placed at the posterior ex-
tremity of the cloak. The external orifice of generation
has not been detected.

The mouth is capable of forming a short proboscis. The
tongue is short, and armed with strong, reflected spines.
The gullet is short, and the stomach, which is lengthened
and folded, is membranaceous. The intestine is several
times longer than the body, and much folded. The liver
is divided into numerous lobes, and intimately united with
the stomach and intestines. The heart is situate at the pos-
terior part of the body. The auricle is placed posteriorly,
and receives the aerated blood from two veins. Each vein
descends along the base of the gills, collecting the aerated
blood from the particular side of the body to which it be-
longs ; and, what is most remarkable, when opposite the
ventricle, it is suddenly enlarged, and sends off a branch

MOLLUSC A. 169

which communicates with it, and again contracts and unites
with its fellow from the opposite side, to form the auricle.
A single aorta arises from the anterior side. The ovarium
is conical, and divided into numerous lobes. Behind, two
ducts seem to arise, and to proceed one to each side ; but
it has not been determined whether they open externally.
No male organs have been detected ; nor is there any thing
accurately known with regard to the peculiar nature of their
hermaphroditism.

GENUS PHYLLIDIA. — Anus placed dorsally near tiie ex-
tremity of the cloak. The body, in the animals of this
genus, is ovate. The foot is narrow in front. The cloak
is broad, coriaceous, and destitute of a shell. Towards its
anterior extremity are two cavities, from which issue the
retractile superior tentacula, as in the genus Doris. Nearly
at the posterior extremity is another cavity, containing the
anus. This opening, though similar in situation to that of
the Doris, is merely a short simple tube. The head is im-
mediately above the anterior margin of the foot, above which
is the mouth, having a small conical feeler on each side.
Under the margin of the cloak on the right side, and about
half way between the mouth and the middle of the body,
are two openings, in a tubercle, for the organs of genera-
tion. The branchiae consist of slender complicated leaves,
which surround the body between the foot and the cloak.
The circle is interrupted at the head and at the tubercle 'if
generation. The mouth is destitute of jaws. The gullet is
simple, ending in a membranaceous stomach. The pylorus
is placed near the cardia, and the intestine goes directly to
the anus. The salivary glands are small, and placed near
the mouth. The liver is large in proportion. The heart is
situate in the middle of the back. The auricle is simple,

170 MOLLUSCA.

placed on the side next the tail, and supplied by the two
systemic veins which collect the aerated blood from the
branchiae on each side. There is a simple aorta arising from
the opposite side of the heart. The organs of generation
appear to be similar to those of the preceding class ; but
they have not as yet been minutely examined. The exist-
ence of eyes is not satisfactorily determined. The animals
of this genus appear to be inhabitants of the tropical seas.
Cuvier has given descriptions and figures of three species,
which differ remarkably from one another in the protuber-
ances of the cloak.

GENUS APLYSIA — Branchiae with a corneous lid. The
body of the Aplysia is ovate, acuminated behind, and pro-
duced before to form a neck. The foot is narrower than
the body. In the middle of the back is a corneous plate
inclosed in a bag in the skin, and on each side, and be-
hind, there is a fold by which this part may be concealed.
The head is slightly emarginate, with a feeler on each side.
The superior feelers are situate on the neck. In front of
each of these is a small black point or eye. The branchiae
are situate underneath the dorsal plate, on the right side,
and exhibit a complicated plumose ridge, capable of expan-
sion beyond the edge of the plate. The anus is situate im-
mediately behind the branchiae, and before these is the ori-
fice of generation, from which proceeds a groove along the
neck to the inferior base of the fore feeler, on the right side,
where there is an opening for the penis. Within the longi-
tudinal lips there are two smooth, corneous plates, the sub-
stitutes for jaws ; the tongue is rough, as in many of the
other gasteropoda. The gullet is short, and suddenly ex-
pands into a large subspiral crop, with membranaceous walls.
To this, a gizzard with muscular walls succeeds, the interior

MOLLUSC A. 171

of which is armed with numerous pyramidal teeth, with ir-
regular summits, of a cartilaginous nature. The connection
between these teeth and the integuments is so slender, that
they are displaced by the application of the smallest force.
They, however, project ,so far into the cavity, as to offer re-
sistance to the progress of the food. There is yet another
stomach, armed on the one side with deflected, pointed, car-
tilaginous teeth. At the pyloric extremity are two mem-
branaceous ridges, between which are biliary orifices, and
the opening into a long narrow caecum, with simple walls,
which is contained within the liver. The intestine is sim-
ple, and after two turns ends in a rectum. The salivary
glands are very long, and, as usual, empty their contents
into the pharynx. The liver is divided into three portions
by the folds of the intestine, each of which consists of seve-
ral lobes. The biliary vessels are very large, and open at
the mouth of the caecum into the last stomach. The food
of the Aplysia consists of sea- weeds and minute shells.

The circulating organs are remarkable. On each side
the body, in the region of the dorsal plate, there is a large
vessel, which receives blood from different parts of the body,
and which likewise, by various openings, has a free com-
munication with the cavity of the abdomen. In this respect
there is a resemblance to the spongy, glandular bodies of
the venae cavae of the Cephalopoda. These two vessels, or
vence cavce, unite posteriorly, and transmit their contents *o
the gills. The aerated blood is now conveyed to an auricle,
of large dimensions, and uncommonly thin walls, situate be-
neath and towards the front of the dorsal plate, and empty-
ing its contents through a valve, into the right side of the
ventricle. The aorta, which issues from the left and an-
terior side, divides into two branches, the smallest of which

172 MOLLUSCA.

proceeds to the liver on the left. The larger branch is again
divided, the smaller branch proceeding to the stomach. The
largest trunk that remains, before it leaves the pericardium,
has two singular bodies attached to it, consisting of com-
paratively large vessels, opening from this aortic branch.
The use of these glands is unknown. The organs of gener-
ation likewise exhibit some remarkable peculiarities. The
ovarium is situate in the posterior part of the abdomen. The
oviduct is tortuous in its course, passes along the surface of
the testicle, and, after uniting with a clavate appendage,
opens into a common canal. The testicle is firm, apparently
homogeneous in its texture, of a yellow colour, with spiral
ridges on its surface. The vas deferens arises from a com-
plex, glandular body, and unites with the common canal.
This common duct, before it reaches the external orifice,
receives the contents of the pedunculated vesicle, and has
attached to it a botryoidal, glandular organ, the use of which
is unknown, but which some suppose to be employed to se-
crete an acrid liquor regarded as venemous. It is obvious
from this structure, that the seminal fluid and eggs must
come in contact in the common canal, and at the single ori-
fice, provided they are both ejected at the same time. From
the orifice to the right fore-feeler there is a sulcus, leading
to the pore containing the retractile penis. This organ,
like those of the other mollusca, is solid. It terminates in
a small filament. The external groove is the only connec-
tion between it and the other sexual organs.

There is a peculiar secretion of a purple fluid which here
deserves to be recorded. It issues from a spongy texture,
underneath the free side of the dorsal plate. Connected
with this cellular reservoir is a glandular body of a consider-
able size, which is supposed to secrete the coloured fluid.

MOLLUSC A. 173

This gland is supplied by a large branch of the glandular
aorta, and gives out two very large veins to the left vena
cava. The fluid itself has never been carefully investigated.
It is not altered by the air after drying, nor is its colour de-
stroyed by acids or alkalis, although the tint is a little
changed, and rendered less pure. Both these reagents pre-
cipitate white flakes from the fluid. This liquor is poured
out by the animal when in danger or constrained, and co-
lours the water for several yards around. It ejects it readily
when put in fresh water ; and when entangled in a net, se-
veral yards of it in the neighbourhood are sometimes stain-
ed, greatly to the amazement of the unsuspecting fishermen.

The Aplysia has been long known in the records of su-
perstition under the name of the Sea Hare. Its flesh, and
the inky fluid it pours out, have been regarded as delete-
rious to the human frame. Even to touch it was supposed
to occasion the loss of the hair ; while the sight of it would
not fail to subdue the obstinacy of concealed pregnancy.
The progress of science has exposed the errors, or perhaps
tricks, of the earlier observers, and proved the innocence of
an animal formerly invested with every repulsive and noxi-
ous attribute. The A. depilans, the type of the genus, is
of frequent occurrence on the British shores. The A.punc-
tata of Cuvier may be regarded merely as a variety.

GENUS DOLABELLA. — Dorsal plate a solid shell.

This genus differs from Aplysia, in the dorsal plate being
calcareous and hard. The fore part of the body is narrow ;
behind it is larger, and obliquely truncated. The disc thus
formed is circular, surrounded with a fringe of fleshy fila-
ments. From the centre of this disc, a longitudinal slit ex-
tends forward, a little way beyond the anterior margin, and

174 MOLLUSCA.

contains the branchiae. The position and structure of the
other organs are precisely similar to those of the Aplysia.
This genus was instituted by Lamark, from characters de-
rived exclusively from the dorsal plate or shell. Cuvier
afterwards examined a species brought from the Mauritius
by Peron, which he considers as the one figured by Rum-
phius in his Amboinshe Rariteitkamer, tab. x. No. 6, and
which he has consecrated to his memory, naming it Dola-
bella Rumphii.

GENUS PLEUROBRANCHUS. — Tentacula two in num-
ber. Cloak and foot expanded, between which, on the
middle of the right side, the branchiae are placed. The cloak
is strengthened in the middle, above the branchiae, by a thin
expanded subspiral shell. The neck is short, and in some
contracted, with the front emarginate, exhibiting the com-
mencement of the inferior tentacula. The upper tentacula
are tubular and cloven. The gills occur at the edge of the
dorsal plate. In front ofohese are the orifices of the organs
of generation, and the anus is situate immediately behind
the gills. The mouth is furnished with a short retractile
proboscis. The tongue occupies both sides of the mouth,
and is covered with spines. The gullet is enlarged into a
kind of crop before it enters the stomach ; this is folded, and
is divided by contractions into three parts. The first sto-
mach has muscular walls of moderate thickness, with a single
longitudinal band. The second has membranaceous walls,
with longitudinal internal ridges, and the third has thin and
simple walls. The gut is short. The salivary glands are
situate at the folds of the stomach, and by two canals empty
their contents into the mouth. The liver is placed on the
stomach, and empties itself into the lower part of the crop.

MOLLUSC A. 175

The heart is nearly in the middle of the back. Its auricle
is on the right side, at the base of the branchiae ; and the
ventricle sends out at the opposite side three arteries.

M. Cuvier has figured and described the P. Peronii with
its anatomical details. Two species likewise appear to be
known as natives of the British seas.

GENUS BULLA. — The head is destitute of tentacula and
the body of the animal, protected by a convoluted shell, is
oblong, becoming a little narrower in front. Below, the foot
is broad, thin, and waved on the margin, expanded on each
side behind, and capable of being turned upwards. At the
posterior part of the foot, but separated from it by a groove,
there is a broad, membranaceous appendage, a part of which
is folded upwards, and a part spread over bodies, like the
foot. It assists in closing the mouth of the shell, and in its
position and use is analogous to the operculum, in the fol-
lowing order. Above the foot, in front, also, but separated
from it by a groove, there is a fat, fleshy expansion, which
Cuvier terms the tentacular disc, considering it as formed
by the union of the inferior and superior tentacula. In the
centre of the disc, in the .Bulla hydatis, (Lin. Trans., vol.
ix. tab. 6, f. 4), Montagu observed two eyes. Between this
portion of the back and the posterior extremity, is the dorsal
plate or shell, forming the genus Bulla of conchologists. In
some species, this shell is covered by the integuments, while
in others it is exposed. But in all, the part containing it is
partially concealed by the animal, by means of the reflected
margins of the foot, and its appendage. Along the right
side of the body there is a groove, formed by the foot and
its appendage, on one side, and the dorsal plate and tenta-
cular disc on the other. The branchiae are situate in a
cavity under the shell or dorsal plate, and resemble those of

176 MOLLUSC A.

the Aplysia. Behind the gills, in the lateral groove, is the
anus ; and in front of these, the orifice of the united organs
of generation. The penis is removed as in the Aplysia, and
connected by a similar slit.

The mouth is, as usual, in front, above the foot and be-
neath the tentacular disc, both of which serve as lips. The
cheeks are strengthened on each side by a corneous plate.
The tongue is well developed in some, as the B. ampulla,
while in the B. qperta it is reduced to a small tubercle.
The gullet is large, and in the B. lignaria makes two folds
before entering the gizzard. This last organ is fortified by
three testaceous plates, convex and rough on the inner sur-
face, and attached to strong, muscular walls. These plates
exhibit in the different species considerable varieties of form
and markings. The intestine, before terminating in the
anus, makes several convolutions in the substance of the
liver. The salivary glands exhibit considerable differences.
In the B. ampulla they are long and narrow, and their in-
ferior extremity fixed to the gizzard. In the B. aperta and
lignaria, they are short, with the extremity free. In the
B. hydatis they are long, unequal, and the extremity of the
one, belonging to the left side, is forked. The liver forms
a part of the contents inclosed in the spire of the shell. It
envelopes the intestine, and empties the bile into its pyloric
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 branchiae. A gland is ob-
served in the Bulla lignaria, similar to the Aplysia, in
which it is probable the fluid is prepared.

MOLLUSCA. 177

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 bear no 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
Bullcea, from such as have the shell in part exposed, which
he retains in the genus Bulla. The shells of the genus
Bullcea 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 DORIDIUM (of Mekel). Destitute of a dorsal plate
or shell. There is a cavity in the cloak, with a spiral turn.
The branchiae, 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.

ORDER II. — BRANCHIAE INTERNAL.

V

The aerating 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 Pectinibranehia of Cuvier, in
eludes nearly all the marine Gasteropoda, which have spiral

178 MOLLUSCA.

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-
taculum. The body of the animal is attached to the shell

MOLLUSC A. 179

by means of two muscles, which adhere to the pillar near
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.

1st 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-

180 MOLLUSCA.

naeus, 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 VELUTINA. — Foot simple. This genus was form-
ed by us for the reception of the Sulla velutina of M tiller,
(Zool. Dan. tab. ci. f. 1, 2, 3, 4), the Helix Icevigata 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.

MOLLUSCA, 181

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.

Family 1. Conusidce. — -Furnished with a long proboscis,
and produced tentacula, with the eyes near the summit on
the outside. The lid is placed obliquely on the foot, and
is too small to fill the mouth of the shell. The genera Co-
nus and Terebellum form this family.

Family 2. Cypreadce. — Cloak enlarged, and capable of
folding over the shell. There is 110 lid. The genus Cy-
prea is the type.

Family 3. Oimladce. — Both extremities of the aperture
canaliculated. The inhabitants of all the genera, Ovula,
Calpurna, and Volva, are unknown. The last genus in-
cludes the Sulla patula of Pennant.

Family 4. Volutadce — Canal of the aperture abbreviated.
Pillar-lip plaited. The foot appears to be destitute of a lid.
The genera are numerous ; Voluta, Oliva, Cymbium, Mar-
ginella, Cancellaria, Mitra, Ancilla, Volvaria, and Torna-
tella. The last genus contains the Voluta tornatilis of Bri-
tish writers.

2. Shell turreted. — The whorls of the shell, the revolving
spire of which is subconical, scarcely embrace one another,
but are merely united at the margins. Three families may
here be established.

Family 1. Buccinidce. — Canal short, scarcely produced
beyond the anterior margin of the lip, and bent towards the
right. The tentacula are remote, and the head is destitute
of a hood. The mouth has a retractile proboscis. The fol-

182 MOLLUSCA.

lowing genera belong to this family : Buccinum, Eburna,
Dolium, Harpa, Nassa, Purpura, Cassis, Morio, Ricinula,
and Monoceros.

Family 2. Muricidce. — Canal produced, and straight.
The tentacula approach the head and mouth as in the pre-
ceding family. The genera are Murex, Typhis, Ranella,
Fusus, Pleurotoma, Pyrula, Fasciolaria, Terebra, Triton-
alia, and Turbinella.

Family 3. Cerithiadce — Canal short and recurved. Head
with a hood. This family contains the marine Cerithium
and Strutheolaria, and the fluviatile Potamidum, Melanop-
sis, and Pirena.

Family 4. Strombusidce — Canal short, and bent towards
the right. The outer margin of the aperture becomes pal-
mated with age, and exhibits a second canal, generally near
the former, for the passage of the head. The following are
the genera : Strombus, Pterocera, Hippocrenes, and Ros-
tellaria.
2d Tribe.
Shell internal.

This tribe consists at present of only one genus, termed
SigaretuS) two species of which are natives of Britain. The
foot of the animals belonging to this genus, or rather of the
species which constitutes the type, is oval, with a duplica-
ture in front. The cloak is broad, with an indentation on
the left side, in front, leading to the branchial cavity. A
ring of transverse muscles unites the cloak with the foot.
On the back is placed the shell, which does not appear on
the outside, as it is covered by a thick cuticle. It is lodged
in a sac, and united by a muscle, which adheres to the pil-
lar. The hood is produced, at each side, into a flattened
tentaculum, with an eye at the external base. The anus is

MOLLUSCA. 183

situate at the branchial indentation on the left side. The
penis is situate on the right side of the neck ; it is external,
with a crooked, blunt, lateral process near its extremity.

The mouth is in the form of a short proboscis. The
tongue is armed with spines, and is long and spirally folded.
The salivary glands are large. The stomach is membrana-
ceous, giving off the intestine near the cardia. The intes-
tine makes two folds. The liver, with the testicle in the
male, and the ovarium in the female, occupy the posterior
part of the body, under the spire of the shell.

2d Subdivision.

Heart traversed by the rectum.

This group includes the order Scutibranchia of Cuvier.
In general form, and in the structure and position of the
branchiae, the resemblance to the genera of the preceding
subdivision is very great. The animals differ, however, in
many particulars. The heart is furnished with two auricles,
and is perforated by the intestine. The sexes appear to be
incorporated in the same individual, or rather the male or-
gans are unknown. The body is protected by a shell, the
aperture of which is wide, and never closed by a lid.

1st Tribe.

Shell ear-shaped, flat, with a lateral, and nearly concealed
spire.

Family Haliotidce. — The genera of this group exhibit well-
marked characters in the shell. In the Haliotis, the left mai -
gin of the shell is pierced by a row of holes. In Padola these
holes are nearly obliterated ; but there is an internal groove and
external ridge in the line of their direction. In Stomatia,
there are neither holes nor ridges. In the Halyotis, the
foot is oval and large. The sides of the body, all round, are
ornamented with one or more rows of simple or branched fila-

184 MOI/LUSCA.

ments. The shell is placed on the back with the spiral part
behind, and the row of holes on the left side, through which
some of the filaments are protruded. The animal is attached
to the shell by a single large muscle. The entry to the
branchial cavity, which likewise contains the termination of
the rectum and oviduct, is on the back. The gills are in two
ridges, consisting of complicated branched filaments. At
the entrance of the cavity, the cloak is furnished with a slit,
the left margin of which rests upon the pillar of the shell.
The edges of this slit are furnished with filaments, which
pass through the anterior holes of the shell. The use of
this singular arrangement is unknown. The branchial ca-
vity likewise contains the viscous organ, in common with
the Pectinibranchiae.

The hood is emarginate, with a long tentaculum on each
side, behind which, towards the side, is a cylindrical protu-
berance, bearing the eye at the top. The mouth is in the
fdrmof a short proboscis, with two corneous plates as cheeks,
and a long narrow tongue extending backwards, and co-
vered with spines. The pharynx is dilatable, with internal
folds. The salivary glands are very small. The gullet is
very short. The stomach is divided into two portions, the
first of which is striated longitudinally with a glandular struc-
ture, and receives a biliary duct. The second is separated
from the former by a valve, is smaller, with transverse striae,
and a double ridge. It likewise receives bile through two
apertures. There is another valve at the pylorus ; and the
intestine, after making some turns, is surrounded by the
heart. There is an auricle on each side, receiving the aer-
ated blood from each of the gills.

2d Tribe.

Shell conical, simple, or slightly revolute at the apex.

MOLLUSCA. 1 85

. Cavity of the shell interrupted by a testaceous plate.
This division consists of five genera, each of which may
be regarded as the type of a family, although, for the pre-
sent, they are all included in one. In the Crepidula, the
gills form a transverse ridge on the roof of the cavity, con-
sisting of filaments extending beyond the margin. The eyes
are at the base of the tentacula. There is only one fluvi-
atile genus, termed Navicella.

B. Cavity of the shell entire.

In the Capulus, the shell is entire, the foot is complicated
on its anterior margin. The shell adheres to the animal by
a circular muscle, leaving an opening in front, for the issue
of the head and entrance to the branchial cavity. The gills
form a single ridge across the roof. The mouth is in the
form of an extended proboscis, with a deep groove above.
The tentacula, which are two in number, have the eyes at
the external base. The anus is on the right side of the
branchial cavity. In the Carinaria, the foot appears to be
compressed, and formed for swimming. The head is co-
vered with a group of tubercles. The mouth is furnished
with a proboscis. Near the middle of the body the shell is
attached. The surface of the body above is closely covered
with small tubercles. It is probable that the species here
alluded to is the same with the Pterotracheq, coronata of
Forskal.

Fissurellada. Shell with a slit or perforation. In the
Fissurella, the apex of the shell is perforated, and united to
the cloak by a circular muscle open in front. The cloak
forms a duplicature in front for the branchial cavity, which
extends to the perforated apex of the shell. The gills con-
sist of two ridges ; at the dorsal extremity of which is the
anus. It is probable that the excrements are ejected at the

1 86 MOLLTJSCA.

perforation in the apex of the Shell, and likewise the water
which enters the branchial cavity in front. The head is fur-
nished with two tentaculae, bearing the eyes at the external
base. The Patella gr&ca and apertura may be quoted as
British examples of the genus.

The genus Emarginula differs from the former in the apex
of the shell not being perforated. Its place, however, is
supplied by a slit on the anterior margin, which is the en-
trance to the branchiae and anus. The foot is surrounded
with a row of filaments, and the eyes are supported on short
footstalks, characters in which it approaches the genus Hal-
yotis. The Patella Jissura of conchologists is considered
,as the type of the genus.

DIVISION II. MOLLUSCA ACEPHALA.

Destitute of a distinct head, or neck.

The animals of this group are much more simple in
their organization than those of the preceding division. In
none of the species are there any rudiments of organs of
hearing or of sight. They are destitute of jaws or other
hard parts about the mouth. They all inhabit the water,
and possess branchiae. The organs of the two sexes are in-
corporated in the same individual, and reciprocal union is
unnecessary. They are either oviparous, or ovoviviparous.
The presence or absence of a shelly covering, furnish cha-
racters for a twofold distribution of the groups.

SECT. 1. — Acephala Conchifera.

The shell in all cases is external and bivalve ; and ex-
hibits very remarkable differences in the form, relative size,

MOLLUSCA. 187

and connection of the valves. The cloak is likewise in the
form of two leaves, corresponding with the valves which
protect it.

ORDER I — BRACHIOPODA.

Mouth with a spiral arm on each side fringed with fila-
ments.

The genera included in this group constitute the Bra-
chiopoda of Cuvier. The lobes of the cloak are free an-
teriorly. From the body, between the lobes, the arms have
their origin at the margin of the mouth. These arms are
capable of folding up spirally. All the species are perma-
nently attached to foreign bodies, and inhabit the sea.
Their nervous and reproductive systems have received but
little elucidation.

1st Subdivision.

Shell supported on a fleshy peduncle.

GENUS LINGULA. Valves equal, the apex of both at-
tached to the peduncle.

The peduncle is nearly cylindrical, cartilaginous, and
covered with a membrane consisting of circular fibres. The
valves are oval, flat, and destitute of teeth, or elastic liga-
ments. The adductor muscles are numerous, obliquely
placed, and appear capable of giving to the valves a con4-
siderable degree of lateral motion. The cloak is thin, and
has interspersed muscular fibres. Its margin is thickened,
and fringed with fine hairs of nearly equal length. The
arms are fleshy in their substance, conical, elongated and
compressed in their form, and ornamented on the external
surface with thick set fringes or tentacula. The mouth is

1 88 MOLLUSCA.

simple, and situate between the arms at their base. There
is no enlargement of the alimentary canal, which can be re-
garded as a stomach, and the anus is a simple aperture situ-
ate on the side. There are marked indications of salivary
glands and a liver. The blood is conveyed to the gills by
two vessels, which are divided at the separation of the lobes
into two branches, one of these going to the half of one
lobe, and another to the opposite half of the other lobe.
Two systemic veins occupy a similar position, and return
the aerated blood to the two lateral systemic ventricles.
The gills themselves are arranged in a pectinated form, on
the inner surface of each lobe of the cloak. There is no-
thing known of the nervous or reproductive systems of this
animal.

The Lingula unguis is the only species of the genus, and
appears to be confined to the Indian seas. The valves were
first figured by Seba, together with the peduncle by which
they are supported. Linnaeus having seen only one valve,
conjectured that it belonged to Patella, and named it P.
unguis. Chemnitz examined both valves, without the pe-
duncle, and pronounced them connected with the genus
Pinna. Bruguiere, aware of Seba's figure,"contemplated the
formation of the new genus for its reception, which Lamark
executed. M. Cuvier afterwards dissected one of the indi-
viduals, which Seba had possessed, and unfolded characters
in its organization, sufficient not only to warrant the con-
struction of a new genus, but a new class.

Some petrifactions have recently been referred to this
genus ; but, in the absence of all vestige of the peduncle,
we do not consider the mere form of the shell as furnishing
characters sufficiently obvious and precise to warrant such
distribution.

MOLLUSCA. 189

TEREBRATULA. Valves unequal, the peduncle passing
through an aperture in the largest valve.

The following interesting information, from the dissec-
tions of Mr. Owen, will be read with pleasure by the student
of the anatomy and physiology of the mollusca.

The mantle adheres very closely to the valves : the lobe
which corresponds to the perforated valve is traversed longi-
tudinally by four large vessels ; the opposite lobe is simi-
larly traversed by two such vessels. Its margins are thick-
ened, not as in the Lamillibranchiate Bivalves from con-
traction, but owing to a peculiar structure connected with
respiration. They are puckered at regular distances, the
puckerings being apparently caused by the insertion of de-
licate cilia, which pass as far within the mantle as they pro-
ject out of it, but which are so minute as to be observable
only by means of a lens. In the interspaces of the cilia the
margin of the mantle is minutely fringed, and within the
fringe is a canal, which extends along the whole circumfer-
ence. From this canal the large vessels of the mantle lobes
take their origin : they may be regarded as the branchial
veins conveying the aerated blood to the two hearts, which
are situated exterior to the liver, and just within the origin
of the internal calcareous loop : they are accompanied in
their course by much smaller vessels, probably the branchial
arteries. Such is apparently the system of respiration in
Terebratula.

The viscera occupy a very small space near the hinge.
The alimentary canal commences by a small puckered
mouth, situated immediately between the folded extremi-
ties of the arms. It passes backwards, and expands into a
membranous stomach, surrounded by the liver, a bulky gland
of a green colour and minute follicular texture, which com-

190 MOLLUSCA.

municates with it by many orifices. The intestine passes
down to the hinge, and then turns to the right side and
terminates between the two mantle-lobes. No trace of a
salivary gland v/as found.

The generation of Terebratula is that of the ordinary
Bivalves. In two of the larger specimens the ova had in-
sinuated themselves between the layers of the mantle, and
partly surrounded the branchial vessels. When so far ad-
vanced they obscure the organization of the mantle which
adapts it for respiration : this organization is consequently
most satisfactorily observed in very young individuals.

The peculiar internal testaceous apparatus or loop con-
nected wTith the hinge and supporting the arms, possesses
some elasticity, and when acted on by the muscles, becomes
in its reflected part sufficiently convex to press upon the
perforated valve and separate it slightly from the opposite
one ; thus compensating for the absence of the thick arms
of Lingula, which, in their protrusion, push open the valves,
and also for that of the elastic fibres, constituting the liga-
ment of ordinary Bivalves.

In the Orbicula lamellosa the same intelligent observer
traced along the whole circumference of the valves, shining
cilia projecting for an extent varying from two to four lines:
they are consequently much longer than in Terebratula and
in Lingula anatina, and are rather longer than in Lingula
Audebardii, Brod. On examination under a higher power
they are observed to be beset with smaller setae, which pro-
bably give them greater power in determining the respira-
tory currents. The mantle is similarly vascular to that of
Terebratula, there being, in the upper lobe, four principal
trunks (comparatively, however, much shorter than in that
genus) ; and two in the lower. These trunks terminate in

MOLLUSCA. 191

sinuses, situated close, and two strong tendinous membranes,
which circumscribe the visceral mass, and to which the
mantle-lobes firmly adhere. Here the veins of both man-
tle-lobes join, and the common trunk or sinus passes oblique-
ly through the membrane, and may be plainly seen distri-
buting ramuli over the liver and ovary.

The muscles and viscera form a rounded mass, situated
in the posterior half of the shell. The mouth is seated be-
tween the base of the arms. The oesophagus passes ob-
liquely through the tendinous wall of the viscera in a direc-
tion towards the upper valve : it becomes slightly dilated,
and is then surrounded by the liver. The intestine is con-
tinued straight to the opposite end of the visceral cavity, is
there again contracted, makes a sudden bend upon itself,
and returns to the middle of the right side of the visceral
belt, which it perforates obliquely* and terminates between
the lobes of the mantle a little below the bend of the arms.
The liver is of a beautiful green colour, and consists of a
congeries of elongated follicles, closely compacted together,
which communicate by numerous orifices with the stomach,
As in Terebratula, there is no salivary gland.

In Lingula Audebardii, Brod., there is also no salivary
gland ; and Mr. Owen is therefore disposed to believe, that
the gland described as such in Lingula anatina by Cuvier,
was only a portion of the liver, from which the colour had
probably been removed by long maceration in spirit.

In the want of salivary glands the Brachiopoda would
seem to agree with the ordinary Bivalves. Destitute, like
them, of any hard parts about the mouth for comminuting
alimentary substances, glands for pouring in a fluid to
blend with the food during that operation, are not wanted.

The nervous system in Terebratula was not detected by

192 MOLLUSC A.

Mr. Owen. In Orbicula two small ganglia were found on
the side of the oesophagus next the perforated valve ; from
which two filaments, accompanying the oesophagus through
the membranous wall, immediately diverge and pass ex-
terior to the anterior shell muscles, proceeding with corres-
ponding arteries to near the heart, beyond which he could
not trace them. A single small ganglion is situated on the
opposite side of the oesophagus, but on a plane posterior to
the preceding ; this is probably the cerebral ganglion for
giving off nerves to the free spiral extremities of the arms,
close to the base of which it is situated.

ORDER II — BIVALVIA.

Mouth destitute of fringed spiral arms.

The animals of this group form the class Conchifera of
Lamark, the Bivalvia of the older naturalists.

The shells exhibit great variety of form and relative size.
They are joined together at the hinge, which is either plain
or toothed, and corresponds in position with the back of the
animal. The connection of the two valves is secured by
the intervention of an elastic horny ligament, the office of
which is to keep the valves open. It is either external or
internal. The valves are closed by means of adductor
muscles, intermixed with tendons, and, passing traversely
through the animal, adhere to the corresponding places in
the inside of each shell. By the contractions of these
muscles the free edges of the valves are brought into con-
tact, at the same time that the ligament is compressed or
stretched, according as it is internal or external. The num-
ber of muscular impressions is employed by Lamark in the
division of the Bivalvia into two orders, Dimyaires and

MOLLUSCA. 193

J»

Monomyaires. This distinction, however, he has not at-
tended to with care, as in his family Mytilacees, which he
includes in his second order, or those having one adductor
muscle, there are obviously two adductor muscles, although
the one is certainly much larger and more complicated than
the other. Besides these impressions of the adductor mus-
cles, there are others connected with the foot and byssus.
The cloak lines the inside of the shells. In some cases it
is entirely open, when the border corresponding with the
free margin of the shell is thickened, and more or less fring-
ed with contractile irritable filaments. In other cases the
cloak hr front is more or less united, and even forms tubu-
lar elongations, which are termed syphons.

Locomotion is denied to many species of this order.
Among these some are immoveably cemented to rocks and
stones, as oysters ; a few are attached by a cartilaginous
ligament, as the Anomiae ; while others are fixed by means
of a byssus. This last organ consists of numerous filaments
issuing from a complicated apparatus in the breast, connect-
ed with a secreting gland and with the shell by the inter-
vention of tendinous bands. The foot is seated a little to-
wards the mouth, is usually tongue-shaped, capable of con-
siderable elongation, with a furrow on its posterior surface.
This organ, where a byssus is present, is considered as
employed in spinning and fixing the threads. When there
is no byssus, it either acts as a sucker, enabling the animal
to crawl among the surface of bodies, or as a paw, to dig
holes in the sand or mud. None of the species can float in
the water. They either crawl or leap, the last kind of
motion being effected by suddenly opening and shutting the
valves. In securing a residence, some of the species bore
into different substances by means of a rotatory motion of the

194 MOLLUSCA.

shell. It was at one time supposed that the dwelling was
formed by a secretion affecting the' solution of the surround-
ing substance. But the very different substances penetrat-
ed by the same species, as limestone, slate-clay, and wood,
forbid us to entertain such a supposition.

The nervous system is here but little developed. The
superior and inferior ganglia, surrounding the gullet, give
rise to all the nervous filaments which proceed through the
body.

The digestive organs are scarcely less simple. The food
is soft and swallowed entire, and either brought to the mouth
by accident, or by eddies produced in the water- by the
opening and shutting of the shells, aided in some cases by
the syphons.

It may be proper here to state, in order to understand
the relative situation of the parts, that, upon laying the ani-
mal upon its back, and opening the cloak, the abdomen
appears to occupy the middle longitudinally, and the bran-
chia to be arranged on each side. The mouth is situated
at the anterior extremity, and consists of a simple aperture
entering into the gullet, or rather stomach*. It is surround-
ed by four flattened moveable tentacula, two of which in
some are in part united with the cloak, while in others they
are free to the base. In their structure they resemble the
branchiae. The stomach is full of cells, the bottom of each
pierced with a biliary duct. A singular organ, termed the
crystalline process, cylindrical, cartilaginous, and transpar^
ent, is found in some species projecting into the cavity of
the stomach. The liver is large, surrounds the stomach,
and pours out its contents by numerous openings. The in-
testine terminates posteriorly by a tubular anus.

The branchiae consist of two ribbands on each side, ex-

MOLLUSCA. 195

tending the length of the body, free on the sides and mar-
gin, and striated transversely. These plates are frequently
of unequal size. The blood is brought to these by means
of pulmonic veins, without the intervention of the heart.
The aerated blood is transmitted to a systemic heart, con-
sisting of one or two auricles, and a ventricle.

The reproductive organs of the Bivalvia, hitherto exam-
ined, consist of an ovarium occupying the sides of the body,
and penetrating the membranes of the cloak. They appear
to have the organs of both sexes incorporated, and to pro-
pagate without intercourse. Lamark is disposed to con-
sider impregnation produced by the male fluid dispersed
through the water ; a supposition unsupported even by
analogy in the animal kingdom. Many species are ovovivi-
parous ; in which case the eggs when ripe pass into the gills,
where they are hatched.

The methodical distribution of the Bivalvia appears to be
attended with peculiar difficulties, in consequence of the
uniformity which prevails in the structure and disposition
of their organs. The characters furnished by the shell,
though useful in the construction of generic as well as spe-
cific distinctions, have been abandoned by those who prefer
a knowledge of the structure, rather than the form of an
animaL The characters derived from the presence of a
byssus? a foot, or syphons, appear to be nearly of co-ordi-
nate importance. M. Cuvier gives the preference to those
founded upon the appearances of the syphon, by the aid of
which the genera may be distributed into five families, an
arrangement which, though liable to some objections, may
be adopted with advantage. These groups, however, may
be considered as occupying a much higher rank, and each
as including numerous families.

196 MOLLUSCA.

1st Subdivision.

Cloak open.

There are no syphons, the anterior margin of the cloak
being as open as the mouth of the shell. When the valves
open, the water comes immediately in contact with the
branchiae and mouth. The margin of the mantle has a
double fringe of filaments.

1st Tribe.

Valves closed by one adductor muscle.

A. Pectenidce. Animals free or fixed only by a byssus.
Furnished with a foot.

Into this family, contemplated by Lamark, the following
ill assorted genera may be placed : Pecten, Lima, Pedum,
Plagiostoma, Vulsella, Placuna, Gryphsea, Perna, Gervil-
lea, Inoceramus, Malleus, and Crenatula.

B. OstreadcB. Shell cemented to foreign bodies. Body
destitute of a foot.

To this family the following genera are related : Ostrea,
Anomia, Spondylus, and Plicatula.

2d Tribe.

Shell closed by two adductor muscles.

The two genera, Avicula and Meleagrina (of Lamark),
form one family of this tribe ; the genus Pinna another ;
and the Arcadae a third, including Area, Pectunculus, Nu-
cula, Cucullaea, Trigonia, and Castalia.

2d Subdivision.

Cloak more or less closed, forming syphons.

The further division of this group depends on the modi-
fications of the syphons, or aperture of the cloak.

1st Tribe.

The union of the cloak forming only one syphon. k This
is situate posteriorly opposite the anus, and serves for the

MOLLUSCA. 197

ejection of the excrements. The other large opening allows
the water to enter to the mouth and gills.

This tribe may be divided into two families. The first,
Mytildce, will include the genera Mytilus, Modiolus, and
Lithodomus, which are furnished with a byssus. The
second, Unioridce, will embrace Unio, Hyria, Anodonta, and
Iridina. They want a byssus.

M. Cuvier is disposed to place in this group the genera
Cardita, Venericardia, and Crassatella.

2d Tribe.

Cloak closed posteriorly, and anteriorly forming three
apertures. The first serves for the passage of the byssus,
and is the largest. The second admits water to the bran-
chiae and mouth ; and the third is opposite the anus. The
valves are closed by one adductor muscle. There are only
two genera belonging to this tribe, Tridacna and Hippopus.

In the two remaining tribes there are three openings in
the cloak. Two of these are posterior, and near each other ;
sometimes, indeed, they are tubular and united. There is
no byssus, but always a foot.

3d Tribe.

Anterior opening large, allowing the water free access to
the mouth and gills, and the feet freedom of motion. The
structure of the animals is yet too imperfectly examined to
enable any one to establish families on permanent charac-
ters. The attempt which Lamark has made may be con-
sidered as a complete failure, independent of the wanton
changes of nomenclature with which it is chargeable, whilst
the efforts of Cuvier have not been attended with greater
success. The following are the principal genera belonging
to this tribe : Chama, Isocardia, Cardium, Donax, Cyclas,

19$ MOLLUSCA.

Corbis, Tellina, Loripes, Lucina, Venus, Capsa, Petricola,
Corbula, and Mactra.

4th Tribe.

Anterior opening small, and not exposing the mouth or gills.

In this tribe the mantle is closed in front ; and even when
the valves are open, neither mouth nor gills are visible. The
anterior opening serves for a passage to the foot, and the
posterior openings, in the form of two long tubes, united by
a common membrane, serve for the entrance and exit of the
water to the mouth and branchiae, and the ejection of the
faeces, the dorsal syphon serving the latter purpose. The
cuticle of the shell covers also the exposed portion of the
cloak, so that, when the animal is removed from the shell,
it remains as a loose membrane on the margin of the valves,
as was first observed by Reaumur. All the genera prefer
concealment, burrowing in sand, mud, or wood, with the
head downwards, and the syphons rising to the surface.
The following genera belong to this tribe : Mya, Lutraria,
Anatina, Glycemeris, Panopea, Pandora, Gastrochena, Bys*
somia, Hiatella, Solen, Sanguinolaria, Pholas, Teredo, Xylo-
phaga, Clavagella, and Fistulana.

SECT. II — Acephala Tunicata*

Covering soft or coriaceous.

The formation of this interesting group of animals was
first publicly announced by Lamark in his Histoire Natu-
relle des Animaux sans Vertebres, torn. iii. p. 80, (1816.)
The labours of Desmarest, Lesueur, and Cuvier, aided by
the descriptions of Ellis and Pallis, paved the way for the
masterly efforts of Savigny, to whom we owe the most ex-
tensive, new, and accurate information yet given concerning
the animals of this group. His observations are contained

MOLLUSC A. 199

in his Recherches Anatomiques sur les Ascidies composees,
et sur les Ascidies simples, inserted in his Memoires sur les
Animaux sans Vertebres, 8vo, Paris, 1816.

The covering of the animals of this group consists of an
external and internal sac or tunic, which are either entirely
united or unconnected, except at the apertures. The sur-
face is smooth in some, and rough in others, and in a few
species defended by an artificial covering of agglutinated
shells and sand. The sacs are furnished with muscular
bands, and are capable of contraction. Some of the species,
by means of contractile movements, float about in the water ;
others, receiving that element into the branchial cavity, and
ejecting it forcibly at the opposite one, push themselves for-
ward. Many, however, are fixed during life to seaweeds
and stones.

The apertures of the tunic are two in number, unless in
the doubtful genus Mammaria. The one, frequently the
largest, is destined for receiving the water into the cavity
to supply the mouth and gills. This is termed the branch-
ial cavity. The other is destined for the exit t)f the water,
the eggs, and the faeces, and termed the anal opening.
These apertures are sometimes placed near each other, at
other times at opposite extremities of the body, and vari-
ously provided with tentacula or valves.

The mouth is simple, destitute of spiral arms, and open-
ing in the anterior of the cavity of the body between the
branchiae, as in the other Acephala, It possesses neither
jaws nor tentacula. The alimentary canal is very simple,
and can scarcely be distinguished into gullet, stomach, and
intestine. The food is soft, and such as the bounty of the
waves bestows. The liver adheres to the stomach, and in
many species is divided into distinct lobes.

200 MOLLUSC A.

The circulating system appears to be reduced to a single
systemic ventricle. The gills cover the walls of the cavity,
in the form of ridges, more or less complicated, and seldom
symmetrical.

The reproductive organs consist of an ovarium, either
simple or complicated, with some additional glands, the uses
of which have not been ascertained. The species are con-
sidered as hermaphrodite, and independent of reciprocal im-
pregnation. They appear not only to be oviparous, but to be
gemmiparous and compound, many individuals being organi-
cally connected, and capable of simultaneous movements.
They are all inhabitants of the sea.

1st Subdivision. — Dichitonida.

Interior tunic detached from the external one, and united
only at the two orifices.

The branchiae are large, equal, and spread on the central
walls of the inner sac. The branchial orifice has an inner
membranaceous denticulated ring, or a circle of tentacula.

1st Tribe.

Body permanently fixed to other bodies.

In this tribe the branchial and anal orifices are not oppo-
site each other, and do not communicate through the bran-
chial cavity. This cavity at its opening is furnished with ten-
tacular filaments. The branchiae are conjoined anteriorly.

A. Simple.

This division includes the genus Ascidia of Linnaeus.
The individuals are independent of each other, and although
they frequently adhere together in clusters, they are desti-
tute of a common covering, or organical connexion.

1. Apertures furnished with four rays.

The animals of this group have the external tunic cori-
aceous, dry, opaque, rough, folded, and frequently covered

MOLLUSCAo 201

with extraneous bodies, or inclosing such. The branchial
orifice has four rays, the anal one the same, or divided trans-
versely. The branchiae are divided longitudinally into per-
sistent regular deep folds.

a. Body pedunculated.

The peduncle, in this division, may be said to have its
rise in the summit of the body, which it serves to suspend.

The abdomen is lateral. The meshes of the branchiae
are destitute of papillae.

GENUS BOLTENIA. — The tentacular filaments of the
branchial circle are compound. There is no liver, and the
ovarium is compound. Only one species is known, B.fusi-
forme. Savigny, Mem. tab. i. f. 1., and tab. v. f. 5. It is
the Vorticella Bolteni of Lin. and the Ascidia Clavata of
Shaw.

b. Body sessile.

M. Savigny describes this group as a genus, which he
terms Cynthia, which he divides into four sub-genera.

(A.) Tentacular filaments of the branchial orifice com-
pound. The folds of the branchiae more than eight in num-
ber. The liver distinct, and surrounding the stomach.
Ovarium divided, with one division at least on each side the
body. The intestine destitute of a rib.

GENUS CYNTHIA — Meshes of the branchiae unchanged
by the folds. C. Momus. Sav. tab. i. f. 2.

GENUS COZSIRA — Meshes of the branchiae interrupted
by the folds. C. Diona of Sav. tab. vii. f. 1 . The Ascidia
quadridentata of Forskal.

(B.) Tentacular filaments of the branchial orifice simple.
The folds of the branchiae eight in number, four on each
side, and the meshes uninterrupted. Intestine strengthen-

202 MOLLUSCA.

ed by a cylindrical rib from the pylorus to the anus. Liver
absent or indistinct.

GENUS STYELA — Ovarium divided, one division at least
on each side. S. Canopus. Sav. tab. viii. f. 1.

GENUS PANDOCIA. — Ovarium single, and situate in the
fold of the intestine. The Ascidia conchilega, a native
species is the type.

2. Apertures with indistinct rays, or more than four.
The external tunic is here soft, easily cut, and translu-
cent. The rays (when existing) of the branchial orifice
amount to eight or nine ; and those of the anal to six at
least. The branchiae are destitute of longitudinal folds.
The tentacular filaments of the branchial circle are simple.
Liver indistinct* Ovarium single.
a. Body pedunculated.

The stalk is here placed at the base, and serves to sup-
port the body, being of an opposite character from that of
the Boltenia.

GENUS CL.AVEIINA. — Branchial and anal orifices with-
out rays. Angles of the branchial meshes simple. Intes-
tine destitute of a rib. The Ascidia clavata of Pallas, and
the A. lepadiformis of Miiller belong to this genus ; the
latter of these is now recorded as a British species*
£ As connected with this group the small Ascidia, figured
and described by Mr. Lister in the Philosophical Transac-
tions for 1834, deserves particular notice, as the following
important observations which he has recorded, sufficiently
indicate. They will indeed be perused with peculiar inter-
est by all who are practically engaged in the study of mol-
luscous animals.

This compound animal occurs in groups that consist of

MOLLUSCA. 203

several individuals ; each having its own heart, respiration,
and system of nutrition, but fixed on a peduncle that branches
from a common creeping stem, and all being connected by
a circulation that extends throughout. Their parts of such
transparency that their interior is easily seen. Their ex-
ternal shape is that of a pouch, compressed at the sides, and
fixed at the hind part of its base upon the peduncle.

Its two openings are in the form of very short tubes ; that
of the mouth at the top of the pouch, and that of the funnel
in front. The longest diameter, from the peduncle to the
space between the openings, is about -085 inch.

The outer covering is a tough coat, a continuation of the
peduncle, more pliable near the openings ; lined interiorly
with a soft substance or mantle, in which a ramifying circu-
lation is very distinct. A great part of the interior is occu-
pied by the branchial sac, which is subcylindrical, flattened
at the sides, and has its axis vertical ; its cavity terminating
upwards in the oval opening, and being closed at the bot-
tom. It is united to the envelope, or to the mantle above
and behind ; the juncture, beginning in front of the oval
opening, extends backwards on each side of it, and then
downwards in two lines ; between these, along the middle
of the back, is a vertical compound stripe, that seemed to
me cartilaginous. At the bottom the sac appears to be en-
veloped by the soft substance of the mantle, but at its sides
and front a vacant space is left between them, that ends in
the opening of the funnel. The branchial sac is more com-
pressed towards its lower part ; and here are placed, exter-
nally to it, the heart on the left, and the stomach and other
viscera on the right side, the vent opening upwards at the
front into the funnel. On its sides and front the sac is per-
forated by four rows of narrow, vertical, irregularly oval

204 MOLLUSCA.

holes or spiracles, about sixteen in each row, placed at less
than the diameter of one apart from each other. Through
these the water, which flows constantly in at the mouth
when its orifice is open, appears to be conveyed to the va-
cant space between the sac and mantle, and it then escapes
at the funnel. The sac seems extremely thin between the
spiracles ; but their edges are thickened, as if cartilaginous ;
and they are lined with closely set ciliae, which, by their
motion, cause the current of water. When these are in
full activity, the effect upon the eye is that of delicately-
toothed oval wheels revolving continually, in a direction
ascending on the right and descending on the left of each
oval, as viewed from without ; but the ciliae themselves are
very much closer than the apparent teeth, and the illusion
seems to be caused by a fanning motion given to them in
regular and quick succession, which will produce the ap-
pearance of waves, and each wave here answers to a tooth.
The spaces between the rows of spiracles are of much more
substance than the intervals of the spiracles ; some liga-
ments are stretched from them across the side cavities to
the mantle, which seem intended to keep the branchial sac-
expanded. These spaces also support finger-like processes,
about eight in a row, that project nearly at right angles into
the central cavity.

The central cavity I shall venture to call the mouth,
though the mouth is said by Cuvier to lie at its bottom.
The large short tube at its opening ends in five or six ob-
scure indentations ; it can be drawn in and closed at the
will of the animal, as can the opening of the runnel. At the
bottom of the tube the entrance of the mouth is guarded by
simple tentacula, some longer, some shorter, ranged subal-
ternately : their number was not ascertained. Whatever

MOLLUSC A, 205

little substances, alive or inanimate, the current of water
brings, flows in unless stopped by the tentacula, and they do
not appear fastidious, to the mouth, and lodge somewhere
on the sides of it. A lively animalcule will sometimes dis-
engage himself by struggling, and dart about in the cavity
till he lodges on some other part ; or, if a morsel is found
unsuitable, it is ejected by the funnel's being closed, and
the branchial sac suddenly contracted vertically. Mostly,
however, whatever part the food lodges on, it travels from
thence horizontally with a steady slow course towards the
front of the cavity, where it reaches a downward stream of
similar materials, and they proceed together, receiving ac-
cessions from both sides, and enter at last at the bottom, the
oesophagus : this is a small flattened tube which carries them,
flowing on in the same way, without any effort of swallow-
ing, towards the stomach. The tube takes a sharp curve
upwards and backwards before arriving there.

It is extraordinary that these particles pass along in the
mouth just behind the spiracles, when the ciliae are in full
activity, without being at all affected by them. I have, in
some positions, seemed to catch a glimpse of a membrane
suspended within, too transparent to be commonly seen.
One may imagine the water to pass to the spiracles, strain-
ed through the meshes of such a membrane, and the food
to be carried along it by invisible villi ; but this is mere
conjecture. The projecting fingers have the effect, whether
intended for such a purpose or not, of detaining some pri-
soners more bulky than the usual food of the animal, for, in
several individuals, I met with small shrimp-like Crustacea
confined between the rows : one escaped during an obser-
vation, another, after three days, seemed as lively as when
first swallowed.

206 MOLLUSCA.

The stomach runs backward horizontally ; its fore-part
had an inflated look when seen from the side, and, when
from below, that of possessing two lateral lobes. The food
after accumulating here was observed to be pressed onward
to the hinder portion, leaving a narrow opake line of con-
nexion with the oesophagus ; the rest of the fore-part, of
which the apparent volume was nearly as before, having an
ochreous tint ; this was inferred to be the liver, enveloping
the stomach above and on the sides, and accords with its
place in other ascidiae and mollusca. The line is continu-
ed by the intestinal canal that rises and then bends forward,
taking the form of a reversed S, and terminates in an as-
cending rectum and sphincter. The faeces are considerable,
as might be expected, where- the food is taken with so little
discrimination. Transparent vessels, that may be supposed
lactaels, ramify along a part of the intestine and meet at a
collection of globular bodies, from whence two flattish lobes
extend backward ; in others these are wanting. From the
meeting of the vessels two branches ran, one downwards
and backwards, which was lost under the stomach, the other
forwards ; and from the direction it took, I suppose it might
communicate with a main stream of blood near the heart.
Some individuals had not the projection above the vent
observable in others.

But the part that struck me as most remarkable in this
creature was the circulation, of which a good view can be
obtained through the transparent coat, for the particles of the
blood are numerous, and, though not uniform in size or shape,
are mostly between '00025 and -0002 inch in diameter, and
approaching to globular. They are easily measured, as in
the intervals between the spiracles, they pass mostly but one
at a time.

MOLLUSC A. 207

The creeping tube, which unites the individuals of a
group, is the channel for two separate currents of blood, an
upward and a downward one, that are flowing at one and
the same time, and that send off each branch to every pe-
duncle : the blood thus passes into the animal by one cur-
rent, while another carries it back. One of these canals
communicates at the termination of the peduncle with the
heart, which is placed, as has been mentioned, near the bot-
tom of the branchial sac on the left side, and consists of a
transparent ventricle, or boyau, running forward and a little
slopping downward, in a channel hollowed to contain it.
Along the whole length of the boyau a part on one side of
its axis seems fixed to the channel, the rest free and con*
tractile.

When the blood entered the heart from the peduncle,
contraction began at the middle of the ventricle, impelling
onward the contents of the fore part ; and the contraction
of the back part followed in the same direction, so as for the
whole to have the effect of one pulsation ; the heart was
then filled again by a flow from the peduncle. The inter-
vals of the pulse were pretty regular in the same individual,
but in different ones they varied from two seconds to one
and a half second. Part of the blood thus impelled formed
a main upward stream along the front of the branchial or-
gan, branching off at each of the horizontal passages between
the rows of spiracles, and at one above them on a line with
the junction to the mantle on each side. All these again
united and formed a downward current behind. The hori-
zontal channels were connected also by the smaller vertical
passages between the spiracles ; the set of the current in
the latter being upwards for the two lower rows, and down-
wards for the two upper ones.

208 MOLLUSCA.

Another larger portion of the blood, on leaving the heart,
immediately divided into many ramifications that spread like
a network over the stomach and intestines and the soft sub-
stance of the mantle. Of these a part run into the horizon-
tal passages above the branchial sac, a part into the descend-
ingback stream ; a large portion, after leaving the intestines,
took a short course, and, collecting into one channel, flowed
into that stream near the bottom, and, all united, then
entered the peduncle and constituted the returning current
that went to circulate in other animals of the group.

After this circulation had gone on for a while the pulsa-.
tions became fainter for a few beats, and the flow slower, and
suddenly, with but a slight pause, the whole current in all
its windings was reversed. .The heart gave the opposite
impulse ; the channel in the peduncle, that before poured
in the blood, now carried it back, and the other the con-
trary, and every artery became a vein. These changes
continued and succeed each other alternately, the average
time of the currents being the same in both directions, but
the period of each varying within a single observation as
much as from thirty seconds to two minutes. The pheno-
menon, like the currents in the Sertulariae, was invariably
met with in every animal of the species that came under my
notice.

Sometimes, when the creeping tube or the peduncle has
been injured, the circulation of an individual is in conse-
quence insulated, but without appearing to impair any of its
functions. I severed one at the part where it joined the pe-
duncle, when for a few seconds the pulsation ceased ; it then
began irregularly and with considerable pauses, and increased
in steadiness as it went on. At first the impulse given by the

MOLLUSCA. 209

heart was towards the front, and the downward back stream,
instead of flowing out at the wound, was poured into the
hinder end of the ventricle ; but when the current was re-
versed part of the blood was driven for a time through the
stump of the peduncle into the water : however, it soon
staunched, and all the vital actions went on as before the
separation, except that at the beginning of every pulsation
there was a slight recoil.

In one case where the circulation did not extend to an-
other animal, one channel, and only one, was open in the
peduncle, and in this a small current ran to and fro accord-
ing to the direction of the impulse given by the heart.
Some animals, which had probably been injured, but were
still connected with other vigorous ones, seemed to be in
course of absorption. One was observed in which the soft
parts were so shrunk as to occupy a small part only of the
tunic ; the currents of its peduncle extended into this mass,
but the heart, or motion of branchiae, was visible. Upon
looking at the same the next day, the tunic was empty, the
soft matter and circulation reaching only to the end of the
peduncle. I also once noticed a flux and reflux of the blood
in a creeping stem, where the current did not communicate
with any animal.

In some of the last mentioned particulars this Ascidia
bears a resemblance to the Sertulariae, and, like them,
it increases by sprouts : the two streams of the stem run
through the bud before its organs are developed. No pro-
per motion was seen in the particles of its blood, like that
of the Sertulariae.

In a sessile Ascidia, nearly half an inch in length, of
which the coat was too rough and opake to allow an inspec-

210 MOLLUSCA.

tion of the branchiae, the circulation was distinctly visible
in the mantle near the openings, and the particles in the
blood were only of about the same size as above.

b. Body sessile.

The branchial orifice with eight or nine rays, and the
anal with six. The angles of the branchial meshes with
papillae. No liver. A cylindrical rib extending from the
pylorus to the anus.

(A.) Tunic and branchial cavity straight.

GENUS PIRENA. — The branchial sac as extended as the
tunic. Stomach not resting on the intestine. P. phusca of
Forskal is the type, to which Savigny has added three other
species. The Ascidia prunum of Miiller, a native species,
may be referred to this genus.

GENUS CIONA. — Branchial sac shorter than the tunic, and
exceeded by the viscera. Ascidia intestinalis, Lin. is a
native example of this genus.

(B.) Tunic turned up at the base.

GENUS PHALLUSIA. — Branchial sac extending beyond
the viscera into the pouch of the sac. Stomach resting on
the mass of viscera. The Ascidia mentula of Miiller, a na-
tive species, is the type.

There are two genera supposed to be nearly related to
the preceding, which are involved in great obscurity. The
genus Bipapilaria of Lamark appears to be pedunculated,
with two apertures, each furnished with three setaceous
tentacula. The Mammaria of Miiller has only one termi-
nal aperture. One species inhabits the British seas.

B. Compound.

The animals included under this division were formerly
inserted in the genus Alcyonium of Linnaeus, and placed

MOLLUSCA. 211

among the Zoophytes. They are compound animals, many
individuals united by a compound integument, and arranged
according to a uniform plan.

In some cases, there is only one system of individuals in
the mass, in other cases, there are many similarly arranged
and contiguous. The tentacular filaments of the branchiae
appear to be distinct. They are destitute of the intestinal
rib which occurs in some of the preceding genera*

1. Branchial Orifice Radiated.

a. Branchial and anal orifices, with six rays.

(A.) Body sessile. The angles of the branchial meshes
furnished with papillae. The thorax, or cavity containing
the branchiae, cylindrical* The abdomen is inferior, with a
stalk. Ovarium sessile, and single*

GENUS DIAZONA. — Body orbicular, with a single system
of animals disposed in concentric cirles.

The substance is gelatinous. The ovarium enclosed in
fold of the intestine. D. violacea of Sav. tab. ii. f. 3.

GENUS POLYZONA. — Body polymorphous, with many sys-
tems disposed subcircularly.

The body is subcartilaginous. The individuals are dis-
posed irregularly around the common centre. Savigny
inadvertently termed this genus Distoma, a name long
pre-occupied amongst the intestinal worms. The Alcyonium
rubrum of Plancus, and the Distomus variolosus of Gaert-
ner, belong to this genus. The last is a native species.

(B.) Body pedunculated*

GENUS SIGLLLINA. — Body a solid cone, consisting of a
single system of many individuals, irregularly disposed, one
above the other.

The thorax is short, and hemispherical. The angles of
the branchial meshes destitute of papillae. The abdomen

212 MOLLUSCA.

is inferior, sessile, and larger than the thorax. The single
ovarium is pedunculated. S. aslralius, Sav. tab. iii. f. 2.,
brought from New Holland, by M. Peron, is the only known
species.

b. Branchial orifice only furnished with six rays.

(A.) Body pedunculated. System single, circular, and
terminal.

GENUS SYNOICUM. — Anal orifice rayed.

The body is cylindrical. The anal orifice has six very
unequal rays ; the three largest forming the exterior mar-
gin of the central star. The stomach is simple. The angles
of the branchial meshes destitute of the papillae. Ovarium
single, sessile attached to the bottom of the abdomen, and
descending perpendicularly. The S. turgens of Phipps is
the type.

GENUS SYDNEUM. — Anal orifice simple and tubular.

The body is inversely conical. The stomach surrounded
with glands. Intestine spirally folded. Ovarium peduncu-
lated. The S. turbinatum is the only known species, and
was sent to Savigny by Leach from the British seas.

(B.) Body sessile, polymorphous.

(a.) Each system with a central cavity.

GENUS POLYCLINUM. — Systems numerous, convex stellu-
lar. Individuals arranged irregularly round the common
centre. Abdomen inferior pedunculated, and less than the
thorax. Ovarium single, pedunculated, and attached to the
side of the abdominal cavity, and drooping.

M. Savigny describes one species from the Mauritius, and
five from the Gulf of Suez.

(b.) Systems destitute of the central cavity, and the an-
gles of the branchial meshes without papillae.

MOLLUSCA. 213

GENUS ALPIDIUM. — Individuals in a single row round the
common centre.

The thorax is cylindrical. The abdomen inferior, sessile,
and of the size of the thorax. Ovarium single, sessile, pla-
ced at the bottom of the abdomen, and prolonged perpendi-
cularly. Savigny divides the genus into two tribes. In the
first, the individuals are simply oblong, with an ovarium
shorter than the body, as A. ficus (Alcyonium ficus, Linn.)
In the second, the individuals are filiform, with an ovarium
longer than the body, as A. effusum of Savigny, tab. xvi. f. 3.

GENUS DIDEMNUM. — Individuals in distinct systems.

The thorax is short and subglobular. The abdomen in-
ferior, pedunculated, and larger than the thorax. The anal
opening is obscure. The ovarium is single, sessile, and
placed on the side of the abdomen. D. candidum and vis-
cosum, from the Gulf of Suez, are the only known species.

2. Branchial Orifice simple.

The species form a thin fleshy crust on stones and sea-
weeds. The individuals are stellularly arranged in distinct
systems. The branchial orifice is circular and undivided.
The abdomen is sublateral, and fixed at the bottom of the
branchial cavity. The intestine is small, and the anus in-
distinct. The angles of the branchial meshes are without
papillae.

GENUS BOTRYLLUS. — Systems furnished with a central
cavity. The systems are prominent, and consist of one or
more regular concentric rows. The ovarium is double,
being attached to each side of the branchial sac.

This genus is subdivided by Savigny into Botrylli stellati,
and Botrylli conglomerati. In the first, where the indivi-
duals are distributed in a single row, there are some species

214 MOLLUSCA.

in which the individuals are cylindrical with approaching
orifices, and the limb of the central cavity not apparent after
death, and probably short, as the B. rosaceus, Leachii and
Borlassii. In other species, the individuals are ovoid, with
remote orifices, and the limb of the central cavity is always
apparent and notched, as B. Schlosseri, stellatus, gemmeus,
and minutus. In the botrylii conglomerate in which the
individuals are disposed in several rows, there is only one
species, B. conglomerate.

GENUS EUCXELIUM. — Systems destitute of a central cavi-
ty. The individuals are distributed in a single row, and the
ovarium is single, sessile, and attached to the side of the ab-
dominal cavity. The E. hospiliolum of Sav. tab. iv. f. 4., is
the only known species,

2. Tribe.

Body free, and moving about in the water.

GENUS PYHOSOMA. — The body is gelatinous, in the form
of a lengthened bag open at the widest end. The individu-
als are arranged perpendicularly to the axis of the central
cavity, super-imposed on one another. The branchial ori-
fice is external, without rays, and with an appendage over
its upper margin. The anal orifice is opposite, and termi-
nates in the central cavity. Branchial sac destitute of folds,
with a membranaceous ring at the entry. The branchiae
are disjoined. The abdomen is inferior to the branchiae,
and not separated by any contraction. Liver distinct, glo-
bular, and retained in a fold of the intestine. Ovarium
double, opposite, and situate at the upper extremity of the
branchial cavity.

M. Savigny divides the species into Pyrosomata verticil-
la', having the individuals arranged in regular prominent rings,

MOLLITSCA. 215

as P. elegans of Lesueur; and Pyrosomata paniculate, hav-
ing the individuals forming irregular circles unequally pro-
minent, as P. giganteum and Atlanticum.

2. Subdivision. Monochtonida.

Inner tunic adhering throughout to the external one.

The body is gelatinous, transparent, and simple. The
branchial cavity is open at both ends, communicating freely
with the anus. The branchial orifice is in the form of a
transverse slit, with one edge in the form of a valve, to ac-
celerate the entrance of the water into the cavity. The
inner tunic is strengthened by numerous transverse muscu-
lar bands, which, by contracting, diminish the diameter of
the cavity, and eject the water from the anal orifice* there-
by propelling the body through the water. The digestive
organs are situate at the inner end of the cavity. The mouth
and rectum are simple ; the former placed between the two
branchiae, the latter directed towards the anal orifice. The
heart is contiguous to the stomach, at the bottom of what
may be termed the branchial sac, and is enveloped in a
membranaceous pericardium. The branchiae are double,
not incorporated with the walls of the sac, but with two folds
of unequal length. The largest is free in the middle, fixed
at each extremity, and opposed to the dorsal groove, and
traverses the cavity obliquely. The other extends from the
base of the first to the extremity of the dorsal groove. The
surface of the branchiae consists of transverse vessels in a
single range in some species, and a double range in others.

When young, many individuals often adhere, and form
chains and circles. But the fully grown individuals are al-
ways detached and single.

This subdivision comprehends the species of the genus
Salpa ; they are exceedingly numerous, and appear to be-

216 MOLLUSCA.

long to many different genera. M. Cuvier has given indi-
cations of some of these, chiefly derived from the shape.
A few are furnished with an elevated crest or fin, as the
Thalia of Brown ; a few have both extremities rounded or
truncated, as Salpa octofera of Cuvier ; others have one ex-
tremity produced, as Holothuria zonaria of Gmelin ; and
even both extremities produced, as Salpa maxima of For-
skal. The Salapa moniliformis, so common in the Heb-
rides, and first recorded as a native by Dr. Macculloch, in
his valuable Description of the Western Isles, vol. ii. p. 188,
and imperfectly figured in its young state, at tab. xxix. fig.
2., appears to be closely allied to the S. maxima of Forskal,
and but very remotely with the S. poly erotica and confeder-
ata with which it is compared. This observer states, that
" It cannot bear to be confined in a limited portion of wa-
ter, as it died even in a ship's bucket in less than half an
hour." With us, in similar circumstances, those taken in
the evening were alive at noon on the following day.

MOLLUSCA. 217

CHAPTER III.

ON MOLLUSCOUS ANIMALS AS OBJECTS OF UTILITY.

Although molluscous bodies furnish many articles of value
to man, scarcely any naturalist has taken the trouble to
enumerate the different purposes to which they have been
applied, or to point out in what manner their usefulness
might be encreased. To the savage, shells furnish some
of his most important instruments. They often answer all
the purposes of a knife, and are extensively employed as a
substitute for iron : with pieces of the more solid bivalves
he points his arrows, and forms his fish-hooks. Even when
farther advanced in civilization, the canaliculated univalves
sometimes constitute the rustic lamp, while the larger scal-
lops are employed by the dairy-maid to skim her milk and
to slice her butter. From the mother-of-pearl shell many
useful and ornamental articles are fabricated ; and calcined
shells were formerly esteemed by physicians as absorbents ;
and are still regarded by the farmer as furnishing a valua-
ble manure.

Shells thus appear to be of some importance in the arts
of life ; but the animals contained in these shells are of far
greater value. As articles of food, shell-fish are extensively
employed by the poor, and even hold a conspicuous place

218 MOLLUSCA.

at the tables of the rich. In many places, they in a great
measure support the children of our maritime population,
and, in the Western and Northern Islands of Scotland, have,
in years of scarcity, prevented the death of thousands.

The kinds chiefly used in this country, as articles of sub-
sistence, are bivalves, belonging to different genera. Among
these the Oyster (Qsirea edulis) holds the most distin-
guished place. This shell-fish is very widely distributed in
nature, being found in the seas of Europe, Asia, and Africa.
But, since the days of the luxurious Romans, the oysters of
Britain have been held in the highest estimation. They
are found on various parts of our coasts, from the southern
shores of England, to the sheltered bays among the Zetland
Islands. They prefer a rough or rocky bottom, in from
five to twenty fathoms water. They are fished up with a
dredge and an open boat; sometimes, when in shallow
water, with a rake or tongs. They are either conveyed
directly to the market, or are placed in artificial ponds of
sea water, where they increase in size, and acquire a fine
green colour. In England this process of fattening, as it is
termed, is chiefly conducted at Colchester, but the oysters
are obtained from the little creeks between Southampton
and Chichester. This fishery on the coast of England is
supposed to give employment to ten thousand people, so
that, independent of the addition which it makes to the
articles of subsistence, it must be regarded as a valuable
nursery for seamen. As an article of food, oysters are
light and easy of digestion, and may be eaten in great num-
bers without inconvenience. They are used either raw or
when pickled. In the last form, they are sent to different
parts of the country, and even constitute an article of ex-
port. In Scotland, the principal oyster fishings are in the

MOLLUSC A, 219

Fifth of Forth ; but we trust the period is not far distant,
when the proprietors on the western coast of Scotland and
the Hebrides will propagate this shell-fish more extensively
on their shores and sheltered bays. Places fitted for their
growth are every where to be met with ; they require no
superintending care ; they would soon furnish an esteemed
dish to their tables, and form a valuable addition to their
trade.

The next shell-fish, in point of importance, as an article
of food, is the Mussel (Mytilus edulis). This animal is
equally widely distributed as the oyster, and is found upon
our coast in the greatest abundance. It is gregarious, being
found in extensive beds, which are always uncovered at low
water. It is found likewise in the crevices of the rocks.
In this fishery women and children are chiefly employed,
and they detach the mussels with an iron hook from the
beds or rocks to which they"adhere by means of fine carti-
laginous threads. In this country they are conveyed di-
rectly to the market ; but in some places of France they
are kept for a time in salt ponds, to fatten like the oyster,
into which, however, they admit small quantities of fresh
water. The flesh of the mussel is of a yellowish colour,
and considered very rich, especially in autumn, when it is in
season. It is eaten in this country either boiled or pickled,
seldom in soup. To the generality of stomachs it is diffi-
cult to digest, and to many constitutions it is deleterious.
It is, however, in the spring, during the spawning season,
that the greatest danger is to be apprehended. This nox-
ious quality was long considered as occasioned by the pea
crab, which is often found within the shell of mussels. It
is now with more propriety attributed to the food of the
mussel, which, at certain seasons, consists chiefly of the

220 MOLLUSCA.

noxious fry of the star-fish ; and likewise to a disease tc
which the animal is subject in spring, under the influence
of which it melts away, and falls from the rocks. Besides
being useful to man as an article of subsistence, the mussel
supplies the fisherman with one ofhis most convenient and suc-
cessful baits. It is keenly taken both by cod and haddock.
To the cod-fish, however, the animal of the horse-mussel
(Modiola vulgaris} is more acceptable.

The following unsuccessful attempt to plant a colony of
mussels is recorded by Mr. Stevenson in his interesting
work, (p. 73,) in which he gives the details of the erection
of the light-house on the Bell- Rock : " When the work-
men first landed upon the Bell-Rock, limpets of a very large
size were common, but were soon picked up for bait.' As
the limpets disappeared we endeavoured to plant a colony
of mussels, from beds at the mouth of the river Eden, of a
larger kind than those which seem to be natural to the
rock. These larger mussels were likely to have been use-
ful to the workmen, and might have been especially so to
the light-keepers, the future inhabitants of the rock, to
whom that delicate fish would have afforded a fresh meal,
as well as a better bait than the limpet ; but the mussels
were soon observed to open and die in great numbers. For
some time this was ascribed to the effects of the violent
surge of the sea, but the Buccinum lapillus, (Purpura,)
having greatly increased, it was ascertained that it had
proved a successful enemy to the mussel. The buccinum,
being furnished with a proboscis capable of boring, was ob-
served to perforate a small hole in the shell, and thus to
suck out the finer parts of the body of the mussel ; the
valves of course opened and the remainder of the fish was
washed away by the sea. The perforated hole is generally

MOLLUSCA. 221

upon the thinnest part of the shell and is perfectly circular,
ofsichampheredform, being wider towards the outward side,
and so perfectly smooth and regular as to have all the ap-
pearance of the most beautiful work of an expert artist. It
became a matter extremely desirable to preserve the mus-
sel, and it seemed practicable to extirpate the buccinum.
But after we had picked up and destroyed many barrels of
them, their extirpation was at length given up as a hope-
less task. The mussels were thus abandoned as their prey,
and in the course of the third year's operations, so success-
ful had the ravages of the buccinum been, that not a single
mussel of a large size was to be found upon the rock ; and
even the small kind which bred there are now chiefly con-
fined to the extreme points of the rock, where it would
seem their enemy cannot so easily follow them."

The Common Cockle (Car Alum edule) would deserve a
place in preference even to the mussel, were it not exclu-
sively confined to our sandy coasts and bays. It is found
lodged in the sand, a few inches below the surface, its place
being marked by a small depressed spot. Women and
children easily dig up this shell-fish with a small spade.
Cockles are sold by measure, and eaten either raw, or boil-
ed, or pickled. They are deservedly esteemed a delicious
and wholesome food in this country, although in France
they are little regarded. They are in season during March,
April, and May, after which they become milky and insipid.
They are not generally used as a bait.

Two kinds of Razor-fish (Solen siliqua and ensisj are in
many places of this country used as food. In Scotland they
are indiscriminately termed Spout-fah. They are found
upon most of our sandy shores, buried about a foot or two
below the surface, and near to the low water mark. Their

222 MOLLUSCA.

place is known by a small hole in the sand. As it is rather
a laborious operation to dig them out, Bosc informs us, that
the fishermen of France throw a small pinch of salt into
their holes, which always remain open by the action of the
respiratory organs ; that they speedily rise to the surface,
and are thrown out by an iron instrument made for the pur-
pose. The fishermen believe that it is the salt which they
wish to avoid ; but it is conjectured, with greater probabi-
lity, that the presence of the salt water, which is thus formed
by the solution of the salt, makes the animal suppose that
its hole is again covered with the tide. This shell-fish was
esteemed by the ancients as a great delicacy. When boiled
or fried, it is certainly a very palatable morsel. When kept
for a few days, it forms an excellent bait for haddock or cod,
and may even be employed for that purpose in a fresh state.
Several species of Gapers (Myce) are used as food both
in Britain and on the Continent, as the Mya arenaria,
known to the fishermen about Southampton by the whimsi-
cal name Old Maids. These shells reside in the mud or
shingle on the shore, and a few inches below the surface.
In some parts of England and Ireland, they are much used,
but, though common in Scotland, they are never sought after.
Another species, the Mya truncata, is also very common on the
coast. It prefers a hard gravelly bottom, in which it lodges
near low water mark. The inhabitants of the northern islan ds
call it Smurslm, and employ it, when boiled, as a supper dish.
It is not so delicate as some of the shell-fish which we have no-
ticed, but it is by no means unpalatable. The Mya declivis
of Pennant is, according to that author, very plentiful in the
Hebrides, and eaten by the gentry of that country. We
suspect that he should have referred to the Mya truncata.
These shells furnish very good baits to the fisherman.

MOLLUSCA. 223

There are several bivalve shells, besides those which we
have mentioned, employed on our coasts as articles of sub-
sistence. The Scallop (Pecten) was held in high estima-
tion by the ancients, and still is sought after in Catholic
countries. The Pecten maximus is frequently used in Eng-
land. It is found gregarious in moderately deep water,
and is taken up by the dredge. It is pickled and barrelled
for sale, and esteemed a great delicacy. The fishermen
suppose that they are taken in the greatest quantity after a
fall of snow. Another species, the Pecten opercularis, is
employed for culinary purposes in Cornwall, where it is
known by the name of Frills or Queens. In the Firth of
Forth this species is frequently dredged up along with oys-
ters, but it is thrown, by the Newhaven fishermen, to the
dunghill, along with sea urchins and star-fish. To this list
we might add the Mactra solida, which is used as food by
the common people about Dartmouth ; and the Venus pul-
lastra, called by the inhabitants of Devonshire, Pullet, and
eaten by them, and known to the inhabitants of the North-
ern Islands by the name of Cullyock, and there used as a
bait. According to Bruguiere, the Anomia ephippium is
used as food at Languedoc, and is there considered as pre-
ferable to the oyster. — But it is now time that we turn our
attention to the univalve shells, in order to ascertain their
value in an economical point of view.

The common Periwinkle (Turbo littoreous) is, in this
country, more extensively used as food than any of the other
testaceous univalves. This shell is easily gathered, as it is
found on all our rocks which are left uncovered by the ebb-
ing of the tide. Children are principally employed in this
fishery, and the shells are sold by measure. They are in
general used after being plainly boiled, and are consumed

224 "MOLLITSCA.

in great quantities by the poor inhabitants on the coast.
The Nerita littoralis is also frequently gathered along with
the periwinkle, as it frequents the same situations. It is,
however, much smaller, and its flesh is not reckoned equally
good.

The Limpet (Patella vulgata} is equally abundant as the
periwinkle, and frequents the same situations on the rocks.
Although used by the ancients as an article of food, it is
seldom brought to market in this country. Among the
villages along the coast of Scotland this shell-fish is fre-
quently used, and its juice, obtained by boiling, mixed with
oatmeal, is held in high estimation. It is considered in
season about the end of May. The chief excellence of the
limpet, however, is as a bait. It is very easily obtained
from the rocks, from which the fisherman detach it with a
knife, and it is eagerly seized by all the littoral fish which
are sought after. To the haddock it is very acceptable.

Several species of Snails (Helix) are employed for culi-
nary purposes. The largest of these, the Helix pomatia,
was a favourite dish among the Romans, who fattened them
with bran sodden with wine. They are still used in many
parts of Europe during Lent, after having been fed with
different kinds of herbs. This species was originally im-
ported into Britain from Italy, and turned out in Surry,
where it has readily multiplied. The Helix hortensis has
also been employed as food. But, we believe that these
two species are chiefly used medicinally, being administered
in consumptive cases. The small species of the genus are
the favourite food of the birds of the thrush kind, either in
a wild or confined state.

The other univalves which we shall notice are of inferior
importance as articles of subsistence. The Fusus antiqtnts.

MOLLUSCA. 225

the largest of the British turbinated shells, is frequently
dredged up with oysters, and, according to Pennant, " is
eaten by the poor, but oflener used for baits for cod, and
ray." It is probably the same species which is noticed by
the Rev. William Fraser, in his view of the Parish of Gigha
and Cara in Argyleshire, vol. viii. p. 48, of the Statistical
Account of Scotland. He says it is a large white welk call-
ed buckle or dog-welk, and used as a bait for cod. The
method of obtaining these shells for bait being ingenious,
and making us acquainted at the same time with several
new habits of the animal, we shall here insert it. " At the
beginning of the fishing (says Mr. Fraser) a dog is killed
and singed, and the flesh, after rotting a little, is cut
into small pieces, and put into creels or baskets made of
hazel- wands for the purpose. These creels are sunk by
means of stones thrown into them. The flesh of the dog,
in its putrid state, is said to attract the welk, which crawls
up round the sides of the basket, and getting in at the top,
cannot get out again, owing to the shape of it, which is
something like that of the wire mouse-trap. After the first
day's fishing, the heads and entrails of the cod, with skate
and dog-fish, are put into the creels, which are visited every
day, the welks taken out, and fresh bait of the same kind
put in, there being no more occasion for dog's flesh." The
Buccinum undatum, and the Purpura lapillus are also em-
ployed as bait, and in years of scarcity as food.

This list of culinary shell-fish is far from complete, even
in so far as it is a British list. The uses of these mollus-
cous animals have seldom been taken notice of by concho-
logists since the days of Schonvelde, more attention having
been directed to the formation of new systems of arrange-

226 MOLLUSCA.

ment, and to the discovery of new species, than to the habits
and uses of those already known.

Independently of the food which we thus obtain from
testaceous animals, they furnish us with the pearl, one of
the most beautiful ornaments of dress. This substance,
equally prized by the savage and the citizen, is composed,
like shells, of carbonate of lime, united with a small portion
of animal matter. Pearls appear to be exclusively the pro-
duction of the bivalve testacea. Among these, all the shells
having a mother-of-pearl inside, produce them occasionally.
But there are a few species which yield them in greater
plenty, and of a finer colour. The most remarkable of these
is the Avicula margaritifera. This shell, which was placed
by Linnaeus among the mussels, is very widely distributed
in the Indian seas ; and it is from it and another species of
the same genus, termed Avicula hirundo, found in the Eu-
ropean seas, that the pearls of commerce are procured. The
Pinna, so famous for furnishing a byssus or kind of thread,
with which garments can be manufactured, likewise pro-
duces pearls of considerable size. They have seldom the
silvery whiteness of the pearls from the Avicula, being usually
tinged with brown. But the shell which in Britain produces
the finest pearls, is theAlasmodon margaritiferum, which was
placed by Linnaeus in the genus Mya. It is found in all
our alpine rivers. The Conway and the Irt in England, the
rivers of Tyrone and Donegal in Ireland, and the Tay and
the Yythan in Scotland, have long been famous for the pro-
duction of pearls. These concretions are found between
the membranes of the cloak of the animal, as in the Avi-
cula, or adhering to the inside of the shell, as in the Unio.
In the former case, they seem to be a morbid secretion of

MOLLUSCA. 227

testaceous matter ; in the latter, the matter seems to be ac-
cumulated against the internal opening of some hole with
which the shell has been pierced by some of its foes. Lin-
naeus, from the consideration of this circumstance, endea-
voured, by piercing the shell, to excite the animal to se-
crete pearl ; but his attempts, though they procured him a
place among the Swedish nobility and a pecuniary reward,
were finally abandoned ; the process being found too tedi-
ous and uncertain to be of any public utility. The largest
pearl of which we have any notice, is'one which came from
Panama, and was presented to Philip II. king of Spain, in
1579- It was of the size of a pigeon's egg. Sir Robert
Sibbald mentions his having seen pearls from the rivers of
Scotland as large as a bean.

Besides yielding us a variety of wholesome food, and valu-
able ornaments, testaceous animals supply us with a beauti-
ful dye. The Purpura of the ancients, according to the
opinion of Rondeletius, confirmed by the' observations of
Cuvier, was chiefly extracted from the shell termed Murex
brandaris. Since the introduction of the cochineal insect,
the use of this dye has been superseded, so that we are now
in a great measure ignorant of the process which the an-
cients employed to extract it. In Britain there are several
kinds of shell-fish, which furnish a dye of this sort, but these
are seldom sought after. Cole, in 1685, published a method
of obtaining it from the Purpura lapillus, to which Mon-
tagu, in the supplement to Testacea Brittanica, has added
several important directions. When the shell is broken in
a vice, there is seen on the back of the animal, under the
skin, a slender longitudinal whitish vein, containing a yel-
lowish liquor. When this juice is applied to linen, by means
of a small brush, and exposed to the sun, it becomes green,

228 MOLLUSCA.

blue, and purple, and at last settles in a fine unchangeable
crimson. Neither acids nor alkalis affect its colour, and it
may be conveniently employed in marking linen, where an
indelible ink is desirable. The Scalaria clathrus (Turbo
clathrus of Linnaeus) also furnishes a purple liquor of con-
siderable beauty, but it is destructible by acids, and gradu-
ally vanishes by the action of light. The Planorbis cor-
neus likewise yields a scarlet dye, but of still less perman-
ency than the scalaria, as all attempts to fix it have hitherto
proved ineffectual.

We cannot conclude this chapter without remarking, that
the study of molluscous animals rises in importance as we
perceive its utility. When we are told, that searching for
shell-fish, and conveying them to the market, give employ-
ment to a British population of upwards of 10,000 ; that
these animals furnish nourishing food to innumerable fami-
lies, and in years of scarcity prevent the horrors of famine ;
we will be disposed to regard with a favourable eye the la-
bours of that naturalist who examines the structure and
economy of those animals, that, from a knowledge of their
nature, he may render them still more subservient to our
purposes.

Even when considered as objects of amusement, mollus-
cous animals are not devoid of interest. In the preceding
division of our subject, we have considered them as appli-
cable to various useful purposes, and expressed our regret,
at the same time, that no one qualified for the task had ever
bestowed on economical conchology an attentive examin-
ation. WTe cannot therefore consider the present condition
of the science as the result of the labours of its practical
admirers. The lovers of this study, as an agreeable amuse-
ment, have at all times been numerous, from the days of

MOLLUSCA. 229

Laelius and Scipio to the present time ; and it is to their
exertions as collectors, that the science is principally in-
debted for its present state of improvement. The colours
of shells are often so intensely vivid, so finely disposed, and
so fancifully variegated, that, as objects of beauty they rival
many of the esteemed productions of the vegetable king-
dom. In their forms they likewise exhibit an infinite va-
riety. While some consist merely of a hollow cup or a sim-
ple tube, others exhibit the most graceful convolutions, and
appear in the form of cones, and spires, and turbans ; and
in another division, shaped like a box, all the varieties of
hinge are exhibited, from that of simple connexion by a
ligament to the most complicated articulation. The forms
of shells are indeed so various, and many of them so ele-
gant, that a celebrated French conchologist warmly recom-
mends them to the attentive study of the architect. " Or,"
says Lamark, " comme 1'extreme diversite des parties pro-
tuberantes de la surface de ces coquilles, ainsi que la regu-
larite et 1'elegance de leur distribution, ne laisse presque
aucune forme possible dont la nature n'offre ici des exam-
ples ; on peut dire que 1'architecture trouveroit dans les
especes de ce genre (C&rithium) de meme que dans celles
des pleurotomes et des fuseaux, un choix de modeles pour
1'ornement des colonnes, et que ces modeles seroient tres
dignes d'etre employes." (Annoiles du JHus. vol. iii. p. 269«)
In this country, however, no such recommendation is ne-
cessary, as many of our beautiful ornaments of stucco, par-
ticularly for chimney-pieces, are copied from the univalve
testacea, and are greatly admired.

But shells, even with all their beauty and elegance, would
never have acquired so much importance in the eyes of
amateurs, had their forms been as difficult to preserve as

230 MOLLUSCA.

the external coverings of the higher classes of animals. It
is both a tedious and a difficult operation to preserve a quad-
ruped, a bird, or a fish, as a specimen for the cabinet, and
even when the task is completed, it is but of temporary dur-
ation. A slow but certain process of dissolution is going on,
which, though invisible for a time to the owner, gradually
destroys the finest collection of these objects. The very
changes of the atmosphere, combined with the attacks of
insects, accelerate the destructive process. But with shells
the case is very different. Composed of particles already
in natural combination, they do not contain within them-
selves the seeds of dissolution, so that for ages they remain
the same. Besides, all that is in general necessary to pre-
pare a shell for the cabinet, "is merely to remove the ani-
mal. When the shell is covered with foreign matter, we
must wash it away with a brush in soap and water ; and it is
frequently necessary to steep the shell for some time in fresh
water, to extract all the salt water which may adhere to it.
After being properly dried it is fit for the shelf of the cabi-
net, and stands in no need of anxious superintendence.

Amateurs are seldom contented with the simplicity of na-
ture. Vitiated in their taste by a fashion which abides by
no rules, they attempt to improve even her most elegant
productions, and delight to exhibit in their cabinets some
of the efforts of their art. As such are in search of inno-
cent amusement, we mean not to dispute about the propriety
of their conduct, but rather shortly to mention, for their edi-
fication, the method generally in use to improve the beauty
of testaceous objects. Many shells, it is true, naturally pos-
sess so fine a polish, that no preparation is considered as ne-
cessary before placing them in the cabinet. Such are the
) Olivce, and the greater number of what is termed

MOLLUSCA. 231

porcellaneous shells. In general, however, it happens that,
when shells become dry, they lose much of their natural
lustre. This may be very easily restored, by washing them
with a little water, in which a small portion of gum arabic
has been dissolved, or with the white of an egg. This is
the simplest of those processes which are employed, and is
used not only by the mere collector, but by the scientific
conchologist. There are many shells of a very plain ap-
pearance on the outside, by reason of a dull epidermis or
skin with which they are covered. This is removed by soak-
ing the shell in warm water, and then rubbing it off with a
brush. When the epidermis is thick, it is necessary to mix
with the water a small portion of nitric acid, which, by dis-
solving a part of the shell, destroys the cohesion of the epi-
dermis. This last agent must be employed with great cau-
tion, as it removes the lustre from all the parts exposed to
its influence. The new surface must be polished with lea-
ther, assisted by tripoli. But, in many cases, even these
methods are ineffectual, and the file and the pumice-stone
must be resorted to, in order to rub off the coarse external
layers, that the concealed beauties may be disclosed. Much
address and experience are necessary in the successful em-
ployment of this last process. But it must be confessed that
the reward is often great. When thus prepared, even the
common mussel is most beautiful.

The arrangement of shells in a cabinet must depend, in a
great degree, on the taste and fortune of the collector. If
ornament is the object in view, it will be indispensably ne-
cessary to have the shells placed in glass cases, where they
may be distinctly seen. But where a collection of shells is
formed for amusement, they may be kept in drawers, each
species placed in a paper case, or in a cup of wood, glass, or

232 MOLLUSCA.

porcelain, with a label attached, intimating its name, and
the place from whence it was obtained. In this manner,
both univalves and bivalves may be conveniently disposed.
But as many of the former are very small in size, it is often
necessary to fix them on pieces of card, that they may be
preserved, and rendered easier of inspection. When neigh-
bouring species are thus brought together, they can be easily
examined with a lens.

About the end of the sixteenth century, many individuals
began to form collections of testaceous bodies. The first
museum of this kind, of any consequence, was begun by
Benedict Ceruto, and afterwards augmented by Calceolari.
An account of the specimens contained in it wras published
by Olivi, in 1585, and, in 1622, Chiocco published plates of
the shells. After this period, in proportion as collections of
testaceous bodies became numerous, various works on shells
made their appearance. These were not published for any
scientific object, but merely to teach collectors the names
of the different specimens in their museums. As works of
this sort, we may mention the Historia Naturalis of John-
ston ; the Gazophylacium Naturce of Petiver ; the Amboin-
she Rariteitkamer of Rumphius ; and the Wondertoonel der
Nature of Vincent. To this list we might add many mo-
dern works, which are termed Systems of Conchology.'

From the labours of this class of conchologists the science
has derived many important advantages. A taste for the
study has been widely extended ; the shells of distant coun-
tries and shores have been brought together ; and numerous
engravings of these bodies have been published. In this
manner the labours of the man of science have been greatly
facilitated, and our knowledge of nature enlarged.
. The formation of a collection of shells is absolutely ne-

MOLLUSCA. 233

cessary to the successful prosecution of the science of con-
chology. To accomplish this, much care and attention are
requisite. Shells must be sought for in their natural situa-
tions, and obtained, if possible, with the animal alive. After
the animal has remained dead in the shell for any length of
time, it loses its lustre and transparency, and becomes less
valuable, either as an object of beauty or curiosity. Hence
the collector must explore the sea-coast, the land, and the
fresh water, in search of the testaceous animals which they
support, for the purpose of obtaining in a perfect state their
calcareous coverings.

The sea contains more species of shells than either the
land or the fresh waters, and presents to the conchologist an
extensive field for observation. Many species of marine
shells frequent the sea-shore, adhere to rocks, stones, or sea
weed, or lodge in the clay or sand. These are termed Lit-
toral shells, and are seldom found in deep water. The lit-
toral shells are easily collected at ebb tide. Those which
burrow in the mud or sand may be detected by a small de-
pression which they leave on the surface as they retire below
it. Other shells live in deeper water. To collect these the
dredge must be employed ; and if the shells be put into sea
water after they are brought up* the animals may afterwards
be examined with ease. Such collectors as have not the
advantage of a dredge, should examine the refuse of fishing
boats, and traverse the sea shore, and search the rejecta-
menta, especially after a storm of wind. The roots of the
larger JFuri, especially F. digitatus, which grows sometimes
in four or five fathoms water, frequently contain a treasure
of the rarer shells.

During the ebb of stream tides, the conchologist ought
to be very diligent. The rocks are then uncovered, and

234 MOLLUSCA.

under the projecting ledges of the strata he will find many
species of shells in very perfect state.

In rocky shores it will prove a useful employment to turn
over the stones which are scattered in the pools, near low
water, and on the under side of these he will find a rich har-
vest of Chitons and Cingulae.

In the tufts of Corallinaqfficmalis, a number of the small-
er shells are found concealed, likewise among the smaller
Fuci and Confervae. When these bodies are brought from
the shore, and put into a glass of sea water, the smaller shells
will soon be perceived by their motions.

When vessels which have been long at sea come into dock
to be cleaned, their bottoms are often covered with shells,
and with sea-weed, containing numerous rare vermes. To
such situations the conchologist should resort ; and in these
he will often be successful in finding the objects of his pur-
suit. In illustration of this remark, we may mention the
circumstance of the vessel employed at the Bell Rock as a
floating light, having had her bottom covered with mussels
three inches and a half in length, and upwards of one inch
in breadth, although she had only been afloat three years
and seven months. She was moored the llth July 1807,
and removed the llth February 1811. Previous to being
moored, she was completely caulked and pitched. The sand
on the shore likewise yields many of the smaller species of
shells, and should be carefully examined with the micro-
scope.

When sea shells are obtained, they should be plunged into
boiling water, to facilitate the extraction of the animal, and
afterwards soaked in it for some time to remove the salt.
They should then be cleaned with a brush, and all extran-
eous matter removed. When the shells are not soaked in

MOLLUSCA. 235

fresh water, the salt remaining soon attracts moisture, which
speedily destroys the ligaments and epidermis.

The land shells are more within the reach of the scientific
collector. To obtain these, he has only to examine the cre-
vices of rocks, the trunks of trees, decayed wood, moss, and
brushwood. In summer, after a shower, the land shells are
most easily procured. The animals come forth to feed on
the moistened blade, and at that time, from their motion,
may be very readily perceived.

The land shells are very easily preserved. Almost all that
is required is the extraction of the animal.

The fresh water shells, though less difficult to procure than
the sea shells, require more trouble than the land shells. A
piece of gauze spread over a ring attached to the end of a
staff, forms a very convenient net for fishing fresh water
shells. By means of this net in the drought of summer, al-
most all the different species of fresh water shells may be
obtained with ease.

The fresh water shells are frequently covered over with
slime or mud, which must be removed by a brush ; and the
animal may be extracted after the shell has been plunged in
boiling water.

Before closing our remarks on the important group of
animals to which we have been directing the attention of
the reader, we shall dedicate a few paragraphs to a brief
notice respecting Fossu, SHELLS.

Besides the shells which are found on the land and in our
lakes, rivers and seas, and termed RECENT SHELLS, there are
relics of many species found in our marl pits and limestone
rocks, always somewhat altered, and which are denominated
FOSSIL SHELLS. While the shells of the former class have been
eagerly sought after, few conchologists, previous to the be

236 MOLLUSCA.

ginning of the present century, directed their attention to
the condition and distribution of the fossil species. Nearly
six hundred species of recent shells have been described as
natives of Britain, while the fossil species furnished by the
strata of the different formations, and which have been ac-
curately described, fall greatly short of that number. There
is, however, reason to believe that the fossil species are even
more numerous than the recent ones.

It would have been a pleasant task for us to have entered
into the details of this most important subject, but our limits
permit us only to trace its outlines. Our remarks, however,
we trust, will prove useful to those who are entering this
fruitful field of investigation, and will embrace some obser-
vations on the systematic characters, condition, situation,
and distribution of these organic remains.

SYSTEMATICAL HISTORY OF FOSSIL SHELLS — The de-
termination of the characters of fossil shells is attended with
no inconsiderable amount of difficulty. The changes which
they have undergone, and their union, in many cases, with
the substance of the rock, having become incorporated with
it, prevent us from ascertaining, with any degree of accuracy,
the peculiar marks by which the species can be character-
ised. No trace of the animal remains to aid us in the inves-
tigation, so that all our distinctions must depend upon the
characters furnished by the shell. This circumstance should
prevent us from placing much confidence on the conclusions
which have been drawn with respect to the resemblance be-
tween fossil species, and those which still exist in a living
state.

The difficulty of determining the fossil species, and the
reluctance to form new genera, rendered the descriptions

MOLLUSCA. 237

of the older writers nearly unintelligible, although their
figures are still useful to refer to. Lamark, aware of the
imperfection of the characters of the genera of recent shells,
as connected with this subject, and possessing a rich cabinet
of the fossil species found jn the neighbourhood of Paris,
devoted much time to the illustration of this subject, and
with great success, as his various papers published in the
Annales du Museum, abundantly testify. In this country,
Parkinson, in his work entitled Organic Remains of a For-
mer World, has added some important illustrations of the
genera of Lamark, and has given some good descriptions of
the species found in our rocks. Mr. Sowerby, in his Mine-
ral Conchology, (published in numbers), has given excel-
lent figures of the British fossil shells ; but we regret to
add, that he has displayed too great anxiety to constitute
species ; and that the rocks in which they are found imbed-
ed are but imperfectly characterised. But as the figures
are well executed, they will prove highly useful to the Bri-
tish mineralogist, by enabling him to refer to them with
confidence, and to give names to those species which he
meets with in the course of his investigations.

CHEMICAL HISTORY OF FOSSIL SHELLS — When we con-
sider the elements of which shells are composed, and the na-
ture of their combination, we might be ready to expect thr.t
fossil shells would differ but little in structure from recent spe-
cies. But the case is widely different. In many instances
the confused foliaceous structure which prevailed in the re-
cent shell, has given place to a new arrangement of the par-
ticles, and the fossil shell exhibits a foliated crystalline struc-
ture. Here solution and precipitation have taken place in
the same spot, or the results have been effected by the slow

238 MOLLUSCA.

operation of the corpuscular forces. In some cases the cal-
careous matter of the shell has become impregnated with
foreign ingredients, or has totally disappeared, leaving in
its place ferruginous or siliceous depositions. But the most
curious circumstance in the chemical history of these fos-
sils, is the preservation of the animal matter of the shell in
its original form and order of arrangement, even when the
calcareous matter of the shell has been changed into com-
pact or granular limestone. This very important fact we
owe to the ingenuity of Mr. Parkinson, who, by treating
the shell for a length of time with greatly diluted acid, ab-
stracted the calcareous matter, and obtained a distinct view
of the cartilaginous membranes of the shell. The student
will in general observe, that the cavities of those shells,
which present an external opening, are filled with the same
sort of matter as the rock in which they are enclosed, while
the cavities, of the multilocular testacea, for example, which
have no external communication, are filled with matter in-
variably of a crystalline structure, even when not different
from the substance of the rock.

GEOGNOSTIC HISTORY OF FOSSIL SHELLS. — It appears
evident that the advancement of this branch of conchology
must, in a great measure, depend on the accurate discrimina-
tion of the fossil species, and the relations of the rocks in which
they are contained. It is only within the last twenty years,
therefore, that our knowledge of this branch of the subject
has been acquired. The members of the Wernerian and
geological societies have contributed largely to our stock of
knowledge : but much yet remains to be brought to light.
The following notices may be regarded as embracing the prin-
cipal facts which have been ascertained.

MOLLUSCA. 239

In those ancient strata upon which all the others are in-
cumbent, and which are called primitive, no remains of
shells, or other relics of organized bodies, have hitherto been
detected. These rocks are therefore supposed to have re-
ceived their arrangement previous to the creation of animals
and vegetables, or to have been so much altered as to have
all traces of organisms obliterated if such existed. In that
group of rocks which rests upon the primitive strata, and to
which mineralogists give the name of transition, fossil shells,
as well as the remains of vegetables, have been observed.
The shells exhibit such striking peculiarities of form, and
bear so remote a resemblance to the recent kinds, that they
are considered as the remains of species which do not now
exist in a living state on the globe. They are much chang-
ed in their texture, and in general intimately united with
the contents of the stratum. They are chiefly found in the
beds of limestone, sometimes also in the grey wacke and clay
slate. In the numerous and ill-characterised series of strata
which are incumbent on the transition class, and to which
some mineralogists attach the term floetz, the remains of
shells are much more numerous. In the older members of
this class, such as the red sandstone and independent coal
formations, the shells, though in a few instances different in
form from those of the preceding class, appear to have be-
longed to one epoch. They are dissimilar to the recent specie?,
and no longer exist in a living state. In the newer members
of this class, such as the gypsum and chalk rocks, the specie?,
in some examples, bear a much closer resemblance to the exist-
ing races, and several species cannot be distinguished, it is al-
leged, from them, by any satisfactory characters furnished by
the shell. The fossil species found in the rocks of the older
members of the class are greatly altered in their texture,

240 MOLLUSCA.

and, in many cases, intimately united with the substance of
the beds ; the shells belonging to the newer members are
much less altered in their form and texture, separate more
readily from the surrounding rocks, and appear like recent
shells somewhat weathered. The shells are found in nearly
all the different kinds of rock, but are more numerous in
the calcareous strata. In the recent or superficial strata,
fossil shells are frequently to be met with. The species
which here present themselves bear so close a resemblance
to the existing kinds, that conchologists are disposed to con-
sider them as the relics of animals which still exist. In
many cases, the prototypes may be found on the neighbour-
ing shore or lake, but in other instances they must be sought
for at a greater distance. These shells are found in beds
of gravel and sand, and likewise in great abundance in shell
marl.

It appears, then, that the shells in the older strata differ
specifically from those which the newer strata contain ; and
that they have belonged to molluscous animals, which no
longer exist in a living state on this globe ; that, in the
newrer strata, the fossil shells bear a closer resemblance to
existing species ; and that in the last formed strata, remains
of species actually existing are to be met with.

In this geological distribution of the remains of testace-
ous animals we may likewise perceive that, in the older
strata, the inequivalved shells are more numerous than the
other kinds; and that the canaliculated univalves are seldom,
if ever, to be met with in the transition or older members
of the floetz series, but that they become more numerous
in the newer members of the floetz rocks, and in the allu-
vial strata. Circumstances of this kind have induced geo-
logists to conclude that different formations could be dis-

MOLLUSC A. 241

criminated by the petrifactions which they contain. From
the difficulty of distinguishing the fossil species, however,
joined with our ignorance of their geographical distribution,
some mineralogists have not permitted their conclusions to
be much influenced by this rule.

It will likewise be observed, that the shells in the newer
strata are but little changed, whilst those in the older rocks
are greatly altered in their texture, and in part obliterated.
The same power which rendered the rock compact or crys-
talline, has likewise exerted its influence on the imbedded
remains. In the newest strata, this power has scarcely be-
gun to operate ; so that the imbedded shells still retain in
perfection their original characters.

In examining a limestone quarry, for example, the stu-
dent will perhaps be surprised to find petrifactions of shells
in the bed of limestone, while, in the sandstone covering,
he witnesses impressions of plants unaccompanied with
shells. In order to gain more correct ideas on this subject,
let him repair to a marl bog, and he will there find the bed
of marl abounding in shells, while in the bed of sand below,
on which it rests, or of peat moss, which covers it, he will
find exclusively the remains of vegetables. Here let him
study the subject, while the strata are yet recent, and while
lapidification is only commencing. There is, however, this
difference between the shells in the marl and those in tht
limestone, that individuals of the former species still exist,
while no living examples of the latter are known.

GEOGRAPHICAL HISTORY OF FOSSIL SHELLS As the

geographical distribution of recent shells is a branch of con-
chology to which few have devoted their attention, and about
which very little is known, we can scarcely expect to find the
geographical distribution of the fossil species more fully illus-

242 MOLLUSCA.

trated. We know, with regard to the recent shells, that
some species which are found in the bays of Norway and
Greenland occur also on the shores of the Mediterranean,,
and that the British Isles have several species in common
with Africa and the West Indies. Still we know not, with
any degree of accuracy, the geographical range of any one
species. Geologists ought, therefore, to exercise a great
degree of caution in drawing conclusions concerning the
original situation of those shells which they find in a fossil
state. When a fossil shell is discovered in the strata of this
country, which bears a close resemblance to the recent shells
of distant seas ; many inquirers, without waiting until they
have established the identity of the species, and without any
precise information with regard to the geographical distri-
bution of that species, conclude that this fossil shell must
have been brought from these distant seas, and conveyed to
its present situation by some mighty torrent. Instances of
this mode of reasoning could easily be pointed out in the
writings of British and Continental mineralogists.
, In every country there are particular animals and vege-
tables, which indicate, by their mode of growth and rapid
increase, a peculiar adaptation to the soil and climate of
that district. Hence we find a remarkable difference in the
animals and plants of different countries. Many shell-fish
have indeed a very wide range of latitude, through wrhich
they may be observed ; but we know, that the same mol-
luscous animals which are natives of Britain, are not found,
as a whole, as natives of Spain, while the molluscous ani-
mals of Africa differ from both. If the same arrangement
of the molluscous animals always prevailed in the different
stages of their existence, then we may expect to find the
fossil shells of one country differing as much from those of

MOLLUSCA. 243

another, as the recent kinds are known to do, so that every
country will have its fossil, as well as its recent testacea.
Few observations illustrative of this branch of the subject
have hitherto been published.

It has often been remarked, that the fossil shells (and the
relics of other animals and plants) found in the strata of this
country, are very different in their appearance from those
shells of the mollusca which at present exist in the country,
but that they bear a close resemblance to the" existing
species of the equatorial regions. This very important ob-
servation has led some to conclude, that the mollusca which
lived in this country at the period of the formation of the
strata in which they are now enclosed, were influenced by
different physical circumstances, from those by which the
forms of the recent kinds are regulated ; while others have
imagined that those shells once lived in the equatorial re-
gions, and that a mighty deluge transported them to their
present situation. This last conclusion can never be ad-
mitted by those who have witnessed the perfect preservation
of the different parts of fossil shells, their valves, spires,
protuberances, and delicate spines, still unbroken. Though
these species no longer exist in a living state in this coun-
try, nor on the globe, we must admit the conclusion of
Werner, with regard to fossil plants, that they lived and
died in the country where their relics are now found.

It would form a very curious subject of inquiry to ascer-
tain the character of those fossil shells which are found kin
the strata near the equator. If they likewise differ from
the recent species of those seas, and if, in appearance, they
resemble or differ from the productions of arctic regions, we
might then speculate, with more success, upon those mighty
revolutions which have taken place on the earth's surface,

244 MOLLUSCA.

and trace in the mineral kingdom the proofs of those changes
which animals and vegetables have experienced. In the
meantime, we would recommend the examination of the
laws which regulate the physical and geographical distribu-
tion of recent shells and molluscous animals, as the most
suitable preparation for investigating the condition of those
extinct races, the memorials of which are preserved in stra-
ta, differing from one another in structure, in position, and
in composition.

CONTENTS OF THE PLATES.

PLATE I — Fig.]. Spirula australis. 2. Octopus cirrhosus. 3. Ar-
gonauta Argo.

PLATE II. — Fig. 4. Nautilus umbilicatus. 5. Hyalea globosa.
6. Pneumodermon diaphanum.

PLATE III — Fig. 7. Clio borealis ; a. ventral aspect; b. dorsal
aspect ; c. tunic opened. 7. Intestines.

PLATE IV.— Fig. 8. Cleodora lanceolata, with its shell. 9. Cym-
bulia Peronii. 10. Helix Cepa, back and front.

PLATE V — Fig. 11. Achatina fasciata. Fig. 12. Limnea octan-
fracta, of the natural size, and with the oral surface magnified.
13. Segmentina lineata; b. natural size ; a. c. magnified.

PLATE VI — Fig. 14- Auricula Mydse. 15. Ampullaria virescens.
16. Testacilla Maugii, a. 6. aspects of the shell. 17. Testacilla
haliotoidea, a. 6. aspects of the shell. Achatina purpurea.

PLATE VII — Fig. 18. Planorbis nitidus; b. natural size ; a. c. mag-
nified. 18. d. Segmentina lineata. 19. Ancylus lacustris.
2. Scyllea pelagica. 21. Tritonia Hombergii.

PLATE VIIL— Fig. 22 — Glaucus radiatus. 23. Dolabella Rhum-
phii shell. 24. Chiton squamosus.

PLATE IX. — Fig. 25. Fissurella annulata. 26. Parmophorus aus-
tralis. 27. Bulla aperta, with the shell.

PLATE X.— Fig. 28. Trochus Pagodus. 29. Turbo rugosus.
30. Natica plicata. 31. Velutina la?vigata. 32. Delphinula cal-
car. 33. Delphinula Lima. 34- Scalaria pretiosa.

246 PLATES.

PLATE XI — Fig. 35. Solarium hybridum. 36. Paludina vivipara.
37. Baccintim laevissimum. 38. Voluta Japonica.

PLATE XII — Fig. 39. Terebra crenulata. 40. Harpa ventricosa.
41. Cassis decussata. 42. Turbinella pyrum. 43. Fusus retro-
versus.

PLATE XIII — Fig. 44 — Fasciolaria traperium. 45. Pyrula per-
versa. 46. Fusus servatus. 47. Murex haustellum. 48. Scis-
surella crispata, natural size and magnified.

PLATE XIV — Fig. 49. Terebratula cranium, a cluster, and inside
of each valve. 51. Unio Pictorum. 52. Crossatella sulcata.
53. Cyclas cornea.

PLATE XV.— Fig. 50. Diceras arictina. 54. Lingula anatina.

PLATE XVI.— Fig. 55. Anatina hispidula. 56. Teredo navalis.
57. Clavellina lepadiformis.

PLATE XVII — Fig. 58. Ciona intestinalis. 59. Ascidia. New
species of LISTER, natural size, and the right side magnified.

PLATE XVIII — Fig. 60. Botryllus polycyclus. 61. Boltenia ovi-
fera. 62. Cynthia momus. 63. Phallusia nigra. 64. Salpa
cristata.

EDINBURGH : Printed by Balfour & Jack.

PLATE. I.

Octopus arrhosus.

JPLATE.1T.

Nautilus

. #!*&.

PLATE III.

PLATE IV.

Hdix

cepa,.

Helix cepa.

PLATE V.

PLATF, vr

Auriada, U.

PLATE VII.

PLATE WT.

22

PLATE DC

PLATE X

29.

PLATES.

Solarium,

watw.

38.

PLATE. JH.

i v % V^^?/>^^ : /^'

y

rftro versus .

Tervbra. crenulata.

PLATE. XBI.

Fusus Hi serratus.

:

PLATE XIV.

o Pictomm.

Cyclfis

Chassa&tta siitmta,.

PIATE XV.

,54.

LwguJa

s arieti/ui.

Teredo tiwcdis.

dayeffina, lepadiformis

PLATE. XVII

Asddui JV. S. Lister.

momiLs.

SaJpa cristcuta,.

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