Chapter III: Introduction (1)

The term “_Conchology_,” in its legitimate usage, is applied to that department of Natural History which has reference to animals with testaceous covering or shells. It is not unfrequently confounded with _Crustaceology_, but the distinction is obvious and radical, lying not more in the composition of the animal’s habitation, than in the organization of the animal itself. This latter, in the _Crustacea_, is of a fibrous nature, and has articulated limbs; the shell, strictly adapted to the members, covers the creature like a coat of mail, is produced at one elaboration, is cast or thrown aside periodically, and, again at one elaboration, renewed; it is moreover composed of the animal matter with phosphate of lime. In the _Testacea_, on the contrary, the inhabitant is of a simple and soft texture, without bones, and is attached to its domicil by a certain adhesive muscular force; this domicil, too, is a permanent one, and is increased, from time to time, by gradual additions on the part of the tenant; while the entire shell, which is distributed in layers, or strata, is a combination of carbonate of lime, with a very small portion of gelatinous matter. Such animals, then, with such shells, form, alone, the subject of a proper “Conchology.”

Writers have not been wanting to decry this study as frivolous or inessential; most unjustly assailing the science itself, on account of the gross abuses which have now and then arisen from its exclusive and extravagant pursuit. They have reasoned much after this fashion:—that Conchology is a folly, because Rumphius was a fool. The _Conus Cedo Nulli_ has been sold for three hundred guineas; and the naturalist just mentioned gave a thousand pounds sterling for one of the first discovered specimens of the _Venus Dione_ (of Linnæus). But there have been men in all ages who have carried to an absurd, and even pernicious extreme, pursuits the most ennobling and praiseworthy.

To an upright and well regulated mind, there is no portion of the works of the Creator, coming within its cognizance, which will not afford material for attentive and pleasurable investigation; and, so far from admitting the venerable error even now partially existing to the discredit of Conchology, we should not hesitate to acknowledge, that while few branches of Natural History are of more direct, _very few_ are of more adventitious importance.

Testaceous animals form the principal subsistence of an immense number of savage nations, inhabitants of the sea-board. On the coast of Western Africa, of Chili, of New Holland, and in the clustered and populous islands of the Southern seas, how vast an item is the apparently unimportant shell-fish in the wealth and happiness of man! In more civilized countries it often supplies the table with a delicate luxury. Nor must we forget the services of the _pinna_ with its web, nor of the _purpura_ with its brilliant and once valuable dye, nor omit to speak of the pearl-oyster, with the radiant nacre, and the gem which it produces, and the world of industry which it sets in action as minister to the luxury which it stimulates.

Shells, too, being composed of particles already in natural combination, have not within them, like flowers and animals, the seed of dissolution. While the preparation of a specimen for the cabinet is a simple operation, a conchological collection will yet remain perfect for ages. These important circumstances being duly considered, in connexion with the universally acknowledged beauty and variety, both of form and colour, so strikingly observable in shells, it is a matter for neither wonder nor regret that these magnificent _exuviæ_, even regarded merely as such, should have attracted, in a very exclusive degree, the attention and the admiration of the naturalist. The study of Conchology, however, when legitimately directed, and when regarding these _exuviæ_ in their natural point of view, as the habitations, wonderfully constructed, of an immensely numerous and vastly important branch of the animal creation, will lead the mind of the investigator through paths hitherto but imperfectly trodden, to many novel contemplations of Almighty Beneficence and Design.

But it is, beyond all doubt, in a geological point of view that Conchology offers the most of interest to the student; and here, by reference to the fair pages of a profound and mighty knowledge to which it has pointed out the searcher after truth, are triumphantly refuted all charges brought against it of insignificance or frivolity.

“In fine, the relations of the mollusca,” says De Blainville, “with the mineral kingdom, and consequently with the mass of the earth which they contribute to form, are not devoid of interest, for without seeking here to resolve the physiological question—whether the conchyliferous mollusca borrow of the inorganic kingdom the calcareous matter which composes their shells, or whether they form it of themselves, it is still certain that they produce, at least, changes upon the surface of the earth by accumulating this material in some places more than in others, and in consequence that they alter the physiognomy of the superficial structure of the globe, the study of which constitutes geognosy.”

“By this,” says Parkinson, “we are taught that innumerable beings have lived, of which not one of the same kind does any longer exist—that immense beds composed of the spoils of these animals, extending for many miles under ground, are met with in many parts of the globe—that enormous chains of mountains, which seem to load the surface of the earth, are vast monuments, in which these remains of former ages are entombed—that, though lying thus crushed together, in a rude and confused mass, they are hourly suffering those changes, by which, after thousands of years, they become the chief constituent parts of gems, the limestone which forms the humble cottage of the peasant, or the marble which adorns the splendid palace of the prince.” Fossil, wood, coral, and shells, are, indeed, as Bergman very forcibly observes, the only true remaining “medals of Creation.”

EXPLANATION OF THE PARTS OF SHELLS.

MULTIVALVE.

A MULTIVALVE shell is composed of more parts than two. Every part of a shell which is connected by a cartilage, ligament, hinge, or tooth, is called a valve of such shell; thus, the Chitons have eight transverse, broad, but very short valves, placed on the back of the animal, and inserted at their sides into a marginal tough ligament. Plate I. fig. 11, _a a a_.

_Operculum_ consists of four small valves on the summit of the Lepas, which shut up the superior orifice; it is in a certain degree stationary, and different from the operculum of univalve shells, which will hereafter be described. Plate I. fig. 1, A. Fig. 9 represents a profile view of the operculum removed from its place, _a_ the front valves, _b_ the back valves. Fig. 10 a front view of the operculum.

_Base_ is that part of the shell by which it is fixed to rocks and other bodies. Plate I. fig. 1 and 2, B B B.—H is a piece of stone to which the base is fixed, and G a piece of wood to which the shells of this section are generally attached.

_Ligament_ is the membranous or tendinous substance by which the valves or parts of the shell are attached. Some multivalve shells are connected by the parts of one valve locking into another. Plate I. fig. 2, D D D. The ligaments vary considerably in their texture, being scaly, prickly, smooth, or punctated.

_Ridges_ are certain convexities in many of the Lepas tribe, sometimes longitudinal and sometimes transverse. Plate I. fig. 1, F F.

_Peduncle._ A sort of stem by which the shells of the Anatifera are attached to wood, &c. It is a membranaceous substance, similar to a bladder but materially thinner, and filled with a liquid which evidently affords nourishment to the animal. Plate I. fig. 2, C C; the peduncle is usually affixed to a piece of wood as represented at G.

_Feelers_ are those crenated arms, evolved from the side of the Anatifera. While the animal is in the water it continually moves its feelers, evidently for the purpose of entangling minute marine insects, as food. Plate I. fig. 2, E E.

_Accessory valves_ are small plates which cover the apex at the hinge of the Pholades, or are situated below the hinge. Plate I. fig. 3, _a_.

_Margin._ A fleshy border in which the valves are attached in the genus Chiton. Plate I. fig. 11, _b b_.

BIVALVE.

Bivalve shells consist of two parts or valves, connected by a cartilage, and a hinge which is generally composed of teeth; those of the one valve locking into a cavity in the other.

The valves of some bivalve shells are formed exactly alike, and others are very different; the one being smooth, the other rugose; one flat and another convex; and often one is shorter than the other.

The shells of the Mya, Solen, Tellina, Venus, and others, have in general both valves alike, while those of the Spondylus, Ostrea, and Anomia, have in general dissimilar valves. The first of these kinds are called equivalve, and the latter inequivalve.

_Equilateral_ shells, are those whose sides are alike, as in the shells of the genus Pecten. Plate II. fig. 2, and Plate VII. fig. 14. This is also exemplified in the Pectunclus.

_Inequilateral valves_ are shells whose sides are unequal; and of different shapes, as in the Mactra, Donax, &c.

_Summit_ is the most elevated point of that part of the shell in which the hinge is placed. Plate I. fig. 4, _i k_.

In naming this the summit we do not follow the axiom of Linnæus, but because we consider it more properly the summit of the shell than the opposite extremity.

_Base_ is the reverse of the above, or that part of the shell immediately opposite the summit. Plate I. fig. 6 and 7, _d d_.

_Sides_, the right and left parts of the valves. Plate I. fig. 6, _c_.

_Posterior slope_ is that part of the shell in which the ligament is situated. In viewing the posterior slope in front, the beaks of the shell retire from view. Plate I. fig. 4, _i_.

_Anterior slope_, that part of the shell opposite the posterior slope; in viewing it in front, the beaks point to the observer. Plate I. fig. 4, _k_.

_Disk_, the convex centre of a valve, or most prominent part of the valve, suppose it with its inside lying undermost. Plate I. fig. 4, _o_.

_Inside_, the concave part of a valve. Plate IV. fig. 6, _m_.

_Muscular impression_ is the impression left on the inside of the valves, by the adhering muscles of the animal. It differs in most shells, according to the shape of the animal, as semi-ovate, round, lunate, elongated, &c. As a specific distinction, it is often of great use; being, with a very few exceptions, alike in shells of the same species. Some shells have only one cicatrix, as the Edible Oyster and Mytilus; others have two, and some few more; the Tellina for example. Plate I. fig. 6 and 8, _e e e e_.

_Lunule._ The lunated depressions, situated in the anterior and posterior slopes. In different species of Venus they are prominent characteristic marks, often of much service in ascertaining a species. Plate I. fig. 4, _b b_.

_Ligament perforation._ The circular aperture, or perforation through which the ligament passes; by which the animal of the Anomia attaches itself to stones and other marine extraneous bodies, it is in general situated in the flat valve, though there are a few exceptions to the contrary. Plate I. fig. 7, _m_.

_Hinge_ is the point at which bivalve shells are united; it is formed by the teeth of one valve inserting themselves between those of the other, or by the teeth of one valve fitting into the cavities or sockets of the opposite one.

It is on the peculiar construction of the _hinge_ that the generic character of bivalve shells is principally founded, together with the general contour of the shell. Plate II. fig. 1 and 3, _q q q_.

_Teeth of the hinge._ Upon the number and relative situation of the teeth principally depend the specific distinctions; they are of various forms, and very differently placed; some are single and large, others numerous and small, orbicular, spatuliform, laminated, &c. Some hinges have no visible teeth, and are termed _inarticulate_.—When a primary tooth has a groove or hollow in its centre, it is called complicated. Plate IV. Fig. 6, _e_; those with few teeth are termed _articulate_. Plate IV. fig. 1 and 12; and those with many teeth _multiarticulate_. Plate IV. fig. 2, 3, 4, &c. Plate I. fig. 6, and 8, _g g g g_.

_Primary teeth_ are those teeth in general situated in the centre of the hinge, and are for the most part broad, large, and distinct, often elevated; and in general are inserted in a cavity in the opposite valve. They however differ very much in some shells, but may easily be distinguished. Plate IV. fig. 1, 3, and 7, _a a a a a_. These are also termed the Cardinal Teeth.

_Lateral Teeth_, Plate IV. fig. 10, are teeth which diverge from the Umbo, and are in general long and flat, often double and divided by a groove or hollow. Plate IV. fig. 2, 4, 6, and 7. _b b b b_.

_Double Teeth_, Plate IV. fig. 1, _c c_.

_Incurved Teeth_ are those which are bent round, as in the single tooth of the Solen. Plate IV. fig. 8, _f f_.

_Recurved Teeth_, are those which are bent backwards, as in the hinge of the Panopea and Spondylus.

_Middle Teeth_, Plate IV. fig. 4, _d d_. These are also termed Cardinal Teeth.

_Numerous Teeth_, are those small upright teeth, set in rows, of which the hinges of all the species of the genus Arca are formed. Plate IV. fig. 10, _k k_.

_Cavity of the Hinge._ The hollow depression in which the ligament of the Ostrea is situated, generally of a triangular form. Plate IV. fig. 11, _g_.

_Ligament_ of the Hinge, or cartilage, is that flexible fibrous substance by which the valves are united, and the hinges kept in their proper places; generally situated under the beaks of the shell. Plate II. fig. 1, 3, and 4, _l l l_; Plate IV. fig. 3, _n_.

_Beak_ is the extreme point of the summit of bivalves, which in many species turns spirally downwards or to the one side, as in some species of Venus, &c. From this circumstance it is seldom the highest part of the shell. Plate II. fig. 5, _r r_.

_Seam._ When the valves are closed, the line of separation between them is so called. Plate II. fig. 6, _t t_.

_Umbo._ That part situated immediately under the _beak_. Plate I. fig. 6, _w_; and Plate II. fig. 4, _w_.

_Ears._ The processes on each side of the beak, in most species of that division of Ostrea, called Pecten; some have one ear very large, and the other small; and some are scarcely observable on one side. Pl. II. fig. 2, _h h_.

_Superior Ear._ Plate IV. fig. 11, _h_.

_Inferior Ear._ Do. do. _i_.

_Margin._ The extreme edge of the whole shell, or the circumference of either valve, all round. Plate I. fig. 4, _p_; and Plate II. fig. 1, _p_.

_Crenulated margin._ That fine notched edge of shells, which unite into notches in the opposite valve, as genus Donax. Plate IV. fig. 6, _m m_.

_Striæ_ are fine thread-like lines, generally on the exterior surface of shells, and are sometimes both longitudinal and transverse. When the striæ of shells appear indistinct, as if worn out, it is termed _obsolete striæ_. In some instances the insides of shells are striated; for example, the Fasciolaria Tulipa. The character of the striæ is often of much use in distinguishing species. Plate II. fig 2, _f_.

_Right Valve_ is that valve which, when viewed with the inside uppermost, has the anterior slope pointing to the right hand. Plate I. fig. 8; and Plate IV. figs. 5 and 6, _B_.

_Left Valve._ The opposite of the above; the anterior slope points to the left hand, when viewed from the inside. Plate IV. figs. 3, 6, 7, 9, &c.

_Length of the Shell_ is taken from the ligament, or the beak, to the opposite margin. For example, Mytilus: it is longer than it is broad, and the Solens are broader than long. Plate I. fig. 5, _u u_; and Plate II. fig. 4, _v v_.

_Breadth_ is measured from the most extreme edge of the anterior and posterior slopes, being in a contrary direction from its length. Many shells are _broader than long_, such as most of the Myæ, Solenæ, Tellinæ, &c.; and the Mytilus, Ostrea, Pinna, &c., are in general longer than broad. Plate I. fig. 5, _v v_. Plate II. fig. 4, _v v_.

_Byssus_, or _beard_, is an appendage composed of filaments of a silky texture, by which some of the Bivalves fasten themselves to their beds, such as the Mytilus, Pinnæ, &c. Plate II. fig. 6, _s_.

UNIVALVE.

The shells called univalve, or those composed of one part only, are far more numerous than the two preceding, both in genera and species; and it requires a considerable degree of attention to discriminate many of the _species_, as they run into each other so much; and they are divested of the strong and distinct character afforded by the teeth of bivalves; besides many of the species there are several varieties.

In the examination of shells of this order, the general contour or outline of the whole shell is the first particular to be attended to, as this leads to those distinctions necessary in the definition of simple, spiral, or turbinated shells, Univalves with a regular spire, and those without a regular spire. The genera of this order are formed principally from the shape of the aperture, taken in conjunction with the general shape of the shell; from the spire being lengthened or depressed, being with or without a canal, the length of the beak and its direction, together with the particular form of the outer lip: the colour of shells only serves as a specific distinction, and cannot in this respect, in all cases, be depended upon, although in others it is an unvarying test. The particular manner in which the spots are disposed frequently characterises species.

_Apex._ The summit, tip, or highest part of the spire. Plate II. figs. 7, 8, 9, _A A A_.

_Base_ is the opposite extremity from the apex, or tip of the spire. In shells with a beak it implies the tip of such beak; Plate II. fig. 11, _B_. In shells without a beak it is understood to be the lower part, as before-mentioned, opposite the apex; Plate II. figs. 8 and 9, _B B_. In the Patella and some others, the base of the shell is that part on which it rests when it is laid on its mouth. In the Dentalium and Teredo it is the wider end.

_Body_ of the shell is the first or lower whorl of the spire, in which the aperture is situated, and is in general longer than the remaining whorls. Plate II. figs. 10 and 12, _F F_; and Plate III. figs. 7 and 9, _F F_.

_Front_ of the shell is that side where the aperture is situated. Plate II. fig. 7, _I_; and Plate III. fig. 8, _I_.

_Back_ is the opposite side to that in which the aperture is placed or turned directly from the observer. Plate III. figs. 5 and 10, _G G_.

The _venter_, or belly, is the most prominent part of the lower whorl or body, generally situated in the vicinity of the lip over the aperture; and formed by the convexity of the aperture. It is in general only made use of in describing shells whose body is large in proportion to the size of the spire. Plate III. figs. 5 and 10, _H H_.

_Sides._ The extreme edges of the shell, when viewed either in front or from the back. Plate II. fig. 11, _K K K K K K K K_. Right side is, when the shell is viewed in front that side next the observer’s left hand. Left side, the side with the aperture in it.

_Aperture_, or mouth, is that part of the lower whorl or body by which the animal protrudes itself. This is one of the principal generic distinctions of Univalve shells, and differs very much in shape; some apertures being rounded, others semilunar, angular, &c. Plate II. figs. 9 and 11, _C C_; and Plate III. figs. 1, 3, and 14, _C C C_. Some apertures have a canal at their base, and others are devoid of it. In various genera it extends the whole length of the shell, as in the Cypræa, and some of the Cones with depressed spires. This in several individuals is either entirely open, or is closed by an operculum or lid, which is usually affixed to the foot of the animal.

_Canal_, or gutter, is the inside of the elongations of the aperture, or both lips of the shell of those species with a beak, in which it forms a concave channel or gutter, running from its commencement in the aperture to the extremity or base. Plate II. figs. 10 and 11, _Q Q_. Plate III. fig. 8, _Q_. Some species are furnished with two canals, one situated at the junction of the outer lip and body, as in the Murex.

_Beak_ is that lengthened process in which the canal is situate; it commences a little higher up, on the outside, than the insertion of the canal in the inside, which is always distinctly marked by the line of the aperture. Plate II. fig. 11, _p_. This process is not so conspicuous in some of the species of Voluta, but is more marked in the genera Murex, Fusus, Pyrula, &c.

_Pillar_, or _columella_, is that process which runs through the centre of the shell in the inside from the base to the apex in most univalve shells, and appears to be the support of the spire: and, indeed, seems to form that part of the shell: it is in general grooved or folded; but, as it is situated in the interior of the shell, a minute description is unnecessary. Plate II. figs. 10 and 12, _M M M M M_; and Plate III. fig. 9, _M M M_. The internal edge of its base is frequently described as having plaits, &c.

_Plaited Columella_ are those folds, or plaits, which are the distinguishing characteristic of the Volutæ and other genera. Plate II. fig. 7, _z_.

_Pillar Lip_ is a continuation of the glossy process with which the aperture is lined, and expanded on the columella. Plate III. figures 7 and 8, _O O_. This is termed the inner lip by some authors.

_Outer Lip._ The expansion, or continuation of the body of the shell on the left margin of the aperture, and is also lined with the glossy process of the aperture. Plate II. fig. 7, _N_; and Plate III. fig. 8, _N N N_. The latter is an example of the alated or winged shells.

_Operculum_, or lid. This is only an appendage to the turbinated or spiral shells affixed to the foot of the animal, sometimes of a testaceous, in others of a horny or cartilaginous substance. It acts as a door or lid, and is calculated for the protection of the animal, when it retires within its dwelling, from the intrusion of its enemies, and adapted to the shape of the aperture, which it closes nicely up: as exemplified in the operculum of the Turbo, and is of a hard, stony appearance. Plate III. fig. 4.

_Spire_ consists of all the whorls of the shell, except the lower one, which, as before observed, is termed the body of the shell. Plate II. fig. 12, _D_; and Plate III. figures 7 and 8, _D D_.

The spire is a prominent feature of the Univalve; and upon its being elevated, depressed, &c., depends much of the generic and specific definition. Adanson, in his ‘Natural History of Senegal,’ says that the external character of the spire varies according to the plane they turn upon, which, he observes, is either horizontal, cylindrical, conic, or ovoid. At the same time, he admits that there are a great many intermediate forms which cannot properly be defined.

It must be remembered that many of the young shells have not the same number of wreaths as the adults; from which it would appear, that the part of the animal nearest the apex never increases in size. The number of wreaths cannot, at all times, be depended upon. A full grown shell may, however, be known from the outer lip, which has generally an unfinished appearance in young shells. Indeed, in all the land and fresh water shells it is a distinct criterion, as they are never complete in the form of the outer lip till full grown.

_Whorl_ is one of the wreaths or volutions of the shell. Plate II. fig. 8, _L_; and Plate III. fig. 10, _L_.

_Depressed Spire_ is when the spire is very flat, as in the shells of the genus Planorbis, &c. Pl. II. fig. 12, _D_; and Pl. III. fig. 5, _S_.

A flat shell is figured in Plate III. fig. 14.

_Involuted Spire_, those shells which have their whorls, or wreaths, concealed in the inside of the first whorl or body, as in some of the Nautili and Cypræa.

_Suture of the Spire_, or whorls, is a fine spiral line, which separates the wreaths or whorls from each other; it is sometimes crenulated, undulated, or sulcated, and not unfrequently elevated or projecting. Plate II. fig. 9, _E E_.

_Reversed_, or _Heterostrophe Spire_, is when the volutions of the spire revolve in the same manner as a common corkscrew, or when the aperture is placed downwards, the nature of the spire runs upwards from the right hand to the left, Plate III. fig. 13.

In some of the more depressed species of Helix, or Nautilus, great attention is requisite in order to ascertain which is really the upper side of the shell, for it is on that side the spiral turns are to be taken from the centre or apex; and, in most instances, this is to be determined by the oblique direction of the aperture to the under part, where the lip rarely extends so far as on the upper part. In fixed shells, such as Serpulæ, there is no difficulty, as the side which is sessile must be considered as the base or under part. Thus, in the Serpula Lucida the fixed part is sometimes very small, and the mouth turns spirally upwards, in a contrary direction to the sun; and therefore must be considered a reversed or heterostrophe shell, the same as if the volutions nearest the mouth had turned laterally upon the centre or fixed ones. This shell, indeed, is most frequently found with regular lateral volutions; and though subject to great variety, with respect to contortions, it invariably turns the aperture one way.

In some species of Nautilus, however, there can be no rule to ascertain whether the shells are dextral or sinistral; for when the aperture is exactly central, the lip embraces the body equally, and the sides of the shell are similar.

_Chambers_ are the cavities divided by partitions, at regular or irregular intervals; as in the Spirula. Plate III. fig. 11, _W W W W W_.

In some of the Serpulæ there are also divisions, but they are not regular as in the Nautili and Spirulæ; and besides, they differ from them in being devoid of a siphunculus or communication between the chambers, the animal forms a complete partition, and adds to its shell, which it would appear to be necessitated to do from its body growing too large for its abode.

Several of the Patellæ have chambers formed of laminous partitions, subspiral cells, or processes; these in general lie horizontally, and are quite open at one end, as in the Patella Testudinaria, the Crepidula, and Calyptræa.

_Umbilicus_ is in general a circular perforation in the base of the lower whorl, or body, of many univalve shells. This is common to most of the Trochi, in some species of which it penetrates from the base to the apex; widest at the base, and gradually tapering to the top. Plate III. fig. 1, _u_.

_Sub-umbilicated_ shells are those which have the umbilicus covered in a greater or less degree by a thin process; which, in some, almost entirely closes the opening or mouth. This character is most commonly to be met with among species of Buccinum and Murex.

Shells which have no umbilicus are termed imperforate.

_Siphunculus_ is that small round perforation which forms a communication between the chambers of the Spirulæ, and penetrates through the whole spire of the shell. Plate III. fig. 11, _v_.

_Varices_ are transverse ribs which cross the whorls of shells in some species of Buccinum, Murex, and Tritonia, and exemplified in the Cassidaria. Varices are formed by the periodical growth of the shells, these being the margin of the outer lip, to which the animal has attached its periodical enlargements. In some species they have more the form of sutures than ribs; this is owing to the margin of the outer lip being but slightly developed.

_Ribs_ are those longitudinal and transverse protuberances which are in many of the univalve shells. Plate III. fig. 12, _R R R R_.

_Teeth_ of univalves, or tooth-shaped protuberances, are fine, white laminæ, or ridges, running spirally backwards, in a parallel direction to each other; those on the exterior lip may, in most instances, be traced through the outside of the shell, and are nearly alike in length. Plate III. fig. 13, _a_.

_Epidermis_ is a skin, or cuticle, covering the exterior surface of shells, destined by nature to protect their surface from being injured. It is membranaceous, somewhat similar to the periosteum which covers the bones of animals. This substance is the production of the animal inhabiting the shell; it is uniformly observed in some species, and not at all in others. Shells with a rugged or uneven surface have almost always this epidermis. In some it is strong, laminated, velvety, fibrous, or rough, often beset with long hairs, and in others very thin, smooth, and pellucid, and admits the colours of the shell to shine through it. In some species it is so dusky that it entirely obscures the beautiful colouring of the shell beneath. Although many shells are very beautiful, even with this cuticle on them, they are much more so when it is removed; but I would by no means advise the collector of shells to remove it, unless he may have several duplicates of the same species; and then he may do it by way of variety. It is always preferable, however, to keep them in a state of nature.

A shell with epidermis is represented in Plate III. fig. _X_; and the effect of the epidermis removed.

All other protuberances, furrows, &c., will be described at the end of this work in a Glossary of Terms used in the Science.

DESCRIPTION OF PLATE IV.

HINGES OF BIVALVE SHELLS.

Fig. 1. Hinge of the Unio pictorum, _a_ Primary tooth, _c c_ double teeth.

Fig. 2. Hinge of the _Solen_. _b_ Lateral teeth.

Fig. 3. Hinge of the Lucina radula, _a a_ Primary teeth, _n_ cartilage.

Fig. 4. Hinge of the _Cardium_. _b_ Lateral tooth, _d d_ middle teeth, _l l_ spines.

Fig. 5. Hinge of the Lutraria.

Fig. 6. Inside of both valves of the _Donax trunculus_. _A_ is the left valve, and _B_ is the right valve, _b_ lateral teeth, _e_ primary complicated tooth, or cleft in the middle, _m m_ crenulated margin.

Fig. 7. Hinge of the _Venus_, _a a_ Primary teeth.

Fig. 8. Hinge of _Spondylus gæderopus_, _f f_ incurved teeth.

Fig. 9. Hinge of Isocardia Cor.

Fig. 10. Hinge of the Pectunculus, _k k_ numerous small teeth; the distinguishing characteristic of the Family _Arcacea_.

Fig. 11. Hinge of the Pecten, _g_ cavity of the hinge, _h_ superior ear, _i_ inferior ear.

Fig. 12. Hinge of _Anomia Ephippium_.

CLASSIFICATION.

CLASS I.

ANNULATA.

FOUR FAMILIES.

Fam.
1. _Dorsalia._ Two genera.
1. Arenicola. Species 1
2. Siliquaria. „ 8

2. _Maldania._ Two genera.
1. Clymene. Species 1
2. Dentalium. „ 21

3. _Amphitritæa._ Four genera.
1. Pectinaria. Species 2
2. Sabellaria. „ 2
3. Terebella. „ 4
4. Amphitrite „ 7

4. _Surpulacea._ Five genera.
1. Spirorbis. Species 6
2. Serpula. „ 26
3. Vermilia. „ 9
4. Galeolaria. „ 2
5. Magilus. „ 2

CLASS II.

CIRRHIPEDA.

ONE FAMILY.

1. _Cirrhipeda._ Ten genera.
1. Tubicinella. Species 1
2. Coronula. „ 5
3. Balanus. „ 30
4. Acasta. „ 4
5. Creusia. „ 3
6. Pyrgoma. „ 1
7. Anatifera. „ 6
8. Pollicipes. „ 6
9. Cineras. „ 1
10. Otion. „ 2

CLASS III.

CONCHIFERA.

TWENTY FAMILIES.

1. _Tubicola._ Six genera.
1. Aspergillum. Species 4
2. Clavagella. „ 4
3. Fistulana. „ 4
4. Septaria. „ 2
5. Teredina. „ 2
6. Teredo. „ 3

2. _Pholadaria._ Two genera.
1. Pholas. Species 18
2. Gastrochæna. „ 3

3. _Solenea._ Four genera.
1. Solen. Species 21
2. Panopea. „ 1
3. Solecurtus. „ 10
4. Glycimeris. „ 2

4. _Myaria._ Two genera.
1. Mya. Species 8
2. Anatina. „ 12

5. _Mactracea._ Seven genera.
1. Lutraria. Species 14
2. Mactra. „ 44
3. Crassatella. „ 11
4. Erycina. „ 2
5. Ungulina. „ 2
6. Solemya. „ 4
7. Amphidesma. „ 45

6. _Corbulacea._ Two genera.
1. Corbula. Species 10
2. Pandora. „ 4

7. _Lithophaga._ Three genera.
1. Saxicava. Species 9
2. Petricola. „ 13
3. Venerirupis. „ 8

8. _Nymphacea._ Ten genera.
1. Sanguinolaria. Species 9
2. Psammobia. „ 21
3. Psammotea. „ 7
4. Tellina. „ 68
5. Tellinides. „ 2
6. Corbis. „ 2
7. Lucina. „ 26
8. Donax. „ 31
9. Capsa. „ 3
10. Crassina. „ 1

9. _Conchacea._ Seven genera.
1. Cyprina. Species 2
2. Cytherea. „ 83
3. Venus. „ 100
4. Veniricardia. „ 5
5. Cyclas. „ 15
6. Cyrena. „ 10
7. Galathea. „ 1

10. _Cardiacea._ Five genera.
1. Cardium. Species 57
2. Cardita. „ 23
3. Cypricardia. „ 5
4. Hiatelia. „ 2
5. Isocardia. „ 4

11. _Arcacea._ Four genera.
1. Arca. Species 41
2. Cucullæa. „ 1
3. Pectunculus. „ 22
4. Nucula. „ 45

12. _Trigonacea._ Two genera.
1. Trigonia. Species 1
2. Castalia. „ 1

13. _Naiadea._ Four genera.
1. Unio. Species 167
2. Hyria. „ 2
3. Anodonta. „ 49
4. Iridina. „ 6

14. _Chamacea._ Three genera.
1. Diceras. Species 1
2. Chama. „ 18
3. Etheria. „ 5

15. _Tridacnea._ Two genera.
1. Tridacna. Species 7
2. Hippopus. „ 1

16. _Mytilacea._ Three genera.
1. Mytilus. Species 42
2. Modiola. „ 32
3. Pinna. „ 15

17. _Mallacea._ Five genera.
1. Crenatula. Species 7
2. Perna. „ 10
3. Malleus. „ 6
4. Avicula. „ 19
5. Meleagrina. „ 2

18. _Pectinea._ Seven genera.
1. Pedum. Species 1
2. Lima. „ 6
3. Pecten. „ 62
4. Plagiostoma. „ 10
5. Plicatula. „ 5
6. Spondylus. „ 21
7. Podopsis. „ 2

19. _Ostracea._ Six genera.
1. Ostrea. Species 49
2. Gryphea. „ 1
3. Vulsella. „ 6
4. Placuna. „ 3
5. Anomia. „ 9
6. Crania. „ 1

20. _Brachiopoda._ Three gen.
1. Orbicula. Species 1
2. Terebratula. „ 13
3. Lingula. „ 1

CLASS IV.

MOLLUSCA.

TWENTY-THREE FAMILIES.

1. _Pteropoda._ Six genera.
1. Hyalea. Species 2
2. Clio. „ 2
3. Cleodora. „ 2
4. Limnacina. „ 1
5. Cymbulia. „ 1
6. Pneumodermon „ 1

2. _Phyllidiacea._ Six genera.
1. Phyllidia. Species 3
2. Chitonellus. „ 2
3. Chiton. „ 63
4. Patella. „ 49
5. Umbrella. „ 2
6. Pleurobranchus. „ 2

3. _Calyptracea._ Seven gen.
1. Parmophorus. Species 4
2. Emarginula. „ 5
3. Fissurella. „ 22
4. Pileopsis. „ 9
5. Calyptrea. „ 9
6. Crepidula. „ 13
7. Ancylus. „ 5

4. _Bullacea._ Three genera.
1. Acera. Species 1
2. Bullæa. „ 2
3. Bulla. „ 19

5. _Aplysiacea._ Two genera.
1. Dolabella. Species 2
2. Aplysia. „ 37

6. _Limacina._ Five genera.
1. Limax. Species 5
2. Vitrina. „ 3
3. Testacella. „ 2
4. Parmacella. „ 2
5. Onchidium. „ 2

7. _Colimacea._ Eleven genera.
1. Helix. Species 203
2. Carocolla. „ 22
3. Achatina. „ 24
4. Anostoma. „ 3
5. Helicina. „ 19
6. Pupa. „ 40
7. Clausilia. „ 15
8. Bulimus. „ 63
9. Succinea. „ 7
10. Auricula. „ 16
11. Cyclostoma. „ 38

8. _Lymnacea._ Three genera.
1. Lymnea. Species 33
2. Physa. „ 10
3. Planorbis. „ 22

9. _Melaniana._ Three genera.
1. Melania. Species 54
2. Pirena. „ 6
3. Melanopsis. „ 3

10. _Peristomiana._ Three gen.
1. Valvata. Species 3
2. Paludina. „ 31
3. Ampularia. „ 13

11. _Neritacea._ Four genera.
1. Neritina. Species 27
2. Nerita. „ 20
3. Navicella. „ 4
4. Natica. „ 36

12. _Ianthinea._ One genus.
1. Ianthina. Species 3

13. _Macrostomiana._ Four gen.
1. Sigaretus. Species 6
2. Stomatella. „ 5
3. Stomatia. „ 2
4. Haliotis. „ 19

14. _Plicacea._ Two genera.
1. Tornatella. Species 6
2. Pyramidella. „ 6

15. _Scalarina._ Three genera.
1. Scalaria. Species 14
2. Vermetus. „ 2
3. Delphinula. „ 5

16. _Turbinacea._ Eight gen.
1. Solarium. Species 7
2. Trochus. „ 99
3. Monodonta. „ 34
4. Turbo. „ 51
5. Planaxis. „ 4
6. Phasianella. „ 12
7. Turritella. „ 21
8. Rotella. „ 7

17. _Canalifera._ Eleven gen.
1. Cerithium. Species 45
2. Pleurotoma. „ 29
3. Turbinella. „ 23
4. Cancellaria. „ 49
5. Fasciolaria. „ 8
6. Fusus. „ 46
7. Pyrula. „ 29
8. Struthiolaria. Species 2
9. Ranella. „ 15
10. Murex. „ 73
11. Triton. „ 31

18. _Alata._ Three genera.
1. Rostellaria. Species 4
2. Pterecera. „ 7
3. Strombus. „ 32

19. _Purpurifera._ Eleven gen.
1. Cassidaria. Species 5
2. Cassis. „ 25
3. Ricinula. „ 9
4. Purpura. „ 62
5. Monoceros. „ 5
6. Concholepas. „ 1
7. Harpa. „ 9
8. Dolium. „ 7
9. Buccinum. „ 66
10. Eburna. „ 5
11. Terebra. „ 24

20. _Columellaria._ Five genera.
1. Columbella. Species 20
2. Mitra. „ 80
3. Voluta. „ 44
4. Marginellæ. „ 24
5. Volvaria. „ 7

21. _Convoluta._ Six genera.
1. Cypræa. Species 118
2. Ovula. „ 12
3. Terebellum. „ 3
4. Ancillaria. „ 4
5. Oliva. „ 63
6. Conus. „ 181

22. _Nautilacea._ Two genera.
1. Spirula. Species 1
2. Nautilus. „ 2

23. _Heteropoda._ Two genera.
1. Argonauta. Species 3
2. Carinaria. „ 3

The American species are designated by a *.

_Pl. 1._

_Parts of Shells_

_P.S. Duval, Lith. Phil^a._
]

_Pl. 2._

_Parts of Shells._

_P.S. Duval, Lith. Phil^a._
]

_Pl. 3._

_Parts of Shells._

_P.S. Duval, Lith. Phil^a._
]

_Pl. 4._

_Hinges of Shells._

_P.S. Duval. Lith. Phil^a._
]

_Pl. 5._

_1. Siliquaria, 2 Dentalium, 3 Pectinaria, 4 Sabellaria, 5 Terebella,
6. Amphitrite, 7 Spirorbis, 8 Serpula, 9 Vermilia, 10 Galeolaria,
11. Magilus, 12. Tubicinella, 13. Coronula, 14. Balanus, 15 Acasta,
16 Creusia, 17 Pyrgoma, 18 Anatifera, 19 Pollicipes, 20 Cineras, 21.
Otion, 22 Aspergillum._

_P.S. Duval, Lith. Phil^a._
]

_Pl. 6._

_1 Clavagella, 2 Fistulana, 3 Septaria, 4 Teredina, 5 Teredo, 6
Pholas, 7 Gastrochæna, 8 Solen 9 Panopea, 10. Solecurtus, 11.
Glycimeris 12 Mya, 13. Anatina, 14 Lutraria, 15 Mactra, 16.
Crassatella, 17 Erycina, 18 Ungulina, 19 Solenimya, 20 Amphidesma,
21 Corbula, 22 Pandora, 23 Saxicava._

_P.S. Duval, Lith. Phil^a._
]

_Pl. 7._

_1. Petricola 2 Venerirupis 3. Sanguinolaria, 4. Psammobia, 5.
Psammotea, 6. Tellina, 7. Tellinides, 8. Corbis, 9. Lucina, 10.
Donax, 11. Capsa, 12. Crassina, 13. Cyclas, 14. Cyrena, 15.
Galathea, 16. Cyprina, 17. Cytherea, 18. Venus, 19. Venericardia,
20. Cardium, 21. Cardita, 22. Cypricardia, 23. Hiatella._

_P.S. Duval, Lith. Phil^a._
]

_Pl. 8._

_1. Isocardia, 2. Cucullea, 3 Arca, 4. Pectuncules 5 Nucula, 6.
Trigonia, 7 Castalia, 8. Unio, 9. Hyria, 10. Anodonta, 11. Iridina,
12 Diceras, 13. Chama, 14. Etheria, 15 Tridacna, 16 Hippopus 17.
Mytilus, 18. Modiola, 19 Pinna, 20. Crenatula, 21. Perna, 22.
Malleus._

_P. S. Duval. Lith. Phil^a._
]

_Pl. 9._

_1. Avicula, 2 Meleagrina, 3 Pedum, 4 Lima, 5 Pecten, 6 Plagiostoma 7.
Plicatula, 8 Spondylus, 9 Gryphea, 10 Ostrea, 11. Vulsella, 12
Placuna, 13 Anomia, 14 Crania, 15 Orbicula, 16 Terebratula, 17
Lingula, 18 Hyalea, 19 Cleodora, 20 Limacina, 21 Cymbulia, 22
Chitonellus, 23 Chiton, 24 Patella, 25 Pleurobranchus, 26 Umbrella,
27 Parmophorus, 28 Emurginula, 29 Fissurella._

_P. S. Duval, Lith. Phil^a._
]

_Pl. 10._

_1 Pileopsis, 2 Calyptera, 3 Crepidula, 4 Ancylus, 5 Bullæa, 6 Bulla,
7 Aplysia, 8 Dolabella, 9 Parmacella, 10 Limax, 11 Testacella, 12
Vitrina, 13 Helix, 14 Carocolla, 15 Anostoma, 16 Helicina, 17 Pupa,
18 Clausilia, 19 Bulimus, 20 Achalina, 21 Succinea, 22 Auricula, 23
Cyclostoma 24 Planorbis, 25 Physa, 26 Lymnea, 27 Melania, 28
Melanospsis, 29 Pirena, 30 Valvata, 31 Paludina, 32 Ampularia, 33
Neritina, 34 Navicella, 35 Nerita._

_P. S. Duval, Lith. Phil^a._
]

_Pl. 11._

_1 Natica, 2 Janthina, 3 Sigaretus, 4 Stomalella, 5 Stomatia, 6
Haliotis, 7 Tornatella, 8 Pyramidella, 9 Vermetus, 10 Scalaria, 11
Delphinula 12 Solarium, 13 Rotella, 14 Trochus, 15 Monodonata, 16
Turbo, 17 Planaxis, 18 Phasianella, 19 Turritella, 20 Cerithium 21
Pleurotoma, 22 Turbinella, 23 Cancillaria, 24 Fasciolaria, 25 Fusus,
26 Pyrula, 27 Struthiolaria, 28 Ranella, 29 Murex, 30 Triton, 31
Rostellaria._

_P. S. Duval Lith. Phil^a._
]

_Pl. 12._

_1 Pteroceras, 2 Strombas, 3 Cassidaria, 4 Cassis, 5 Ricinula, 6
Purpura, 7. Monoceros, 8 Concholepas, 9 Harpa 10 Dolium, 11 Buccinum
12 Eburna, 13 Terebra, 14 Columbella, 15 Mitra, 16 Voluta 17
Marginella 18 Volvaria, 19 Ovula, 20 Cyprea, 21 Terebellum, 22
Ancillaria, 23 Olivia, 24 Conus, 25 Spirula, 26 Nautilus 27
Argonauta, 28 Carinaria._

_P. S. Duval, Lith. Phil^a._
]

CONCHOLOGY.

CLASS I.
ANNULATA.

Animal soft, elongated, vermiform, naked or inhabiting a tube, which it never entirely quits; the body furnished either with segments or transverse wrinkles; often without a head, eyes or antennæ; without articulated feet, but most of them having in their place bristly, retractile knobs, disposed in lateral rows: mouth subterminal, either simple, orbicular, with lips, or in the form of a proboscis; often with jaws, a knotted longitudinal medulla, and nerves for sensation and motion; the blood red, circulating by means of arteries and veins: respiration by external or internal branchiæ, which are sometimes imperceptible. _Four Families._

FAMILY I.

DORSALIA. Two Genera.

1. Genus _Arenicola_.

_Animal._ The gills, or respiratory organs dorsal, or disposed lengthways on the body.

_Shell._ Supposed to be tubular. One species.

Arenicola piscatorium.

2. Genus _Siliquaria_. Pl. V.

_Animal._ See Arenicola.

Shell very thin, conical, tubular, involuted in a spiral manner, loosely and irregularly; aperture circular, sharp edges, interrupted in the middle by a notch, extending like a slit through the greater portion of its length, and stopping abruptly at some distance from the summit. Inhabits the Indian seas. Eight species.

Siliquaria anguina. S. muricata. S. lævigata. S. lactæa. S. rugosa. S. terebella. S. lima. S. spinosa.

FAMILY II.

MALDANIA. Two Genera.

1. Genus _Clymene_.

_Animal._ Respiratory organs not determined, supposed to be at the posterior part of the body.

_Shell._ Tube thin and slender, open at both ends, encrusted externally with sand and fragments of shells. One species.

Clymene amphistoma.

2. Genus _Dentalium_. Pl. V.

_Animal._ Body elongated, conical, sub-vermiform, enveloped in a fistula mantle as far as the anterior third, and ending in a bourrelet pierced in its middle by an orifice with fringed edges; foot altogether anterior, proboscidiform, terminated by a conical appendage, contained in a kind of cup with festooned edges; head distinct, oval, with a terminal mouth in the middle of a digitated lip; a pair of lateral jaws, formed each of two little oval shells garnished with points.

_Shell._ Tubular, regular, symmetrical, slightly curved longitudinally, tapering gradually to the rear, and opening in a round orifice at each end. Inhabits the British seas. Twenty-one species.

Dentalium elephantinum. D. aprinum. D. sulcatum. D. fasciatum. D. pseudo-antalis. D. radicula. D. antalis. D. arictinum. D. octogonum. D. deforme. D. novemcostatum. D. sexangulaire. D. striatum. D. dentalis. D. corneum. D. nigrum. D. politum. D. eburneum. D. clava. D. fissura. D. coarctatum.

FAMILY III.

AMPHITRITÆA. Four Genera.

1. Genus _Pectinaria_. Pl. V.

_Animal._ Respiratory organs in general known, and disposed at or near the anterior part of the body; not separated or covered by an operculum.

_Shell._ A membranous papyraceous tube in the form of a reversed cone; unfixed; exterior covered with sandy adhesions. Two species.

Pectinaria capensis.

P. belgica.*

2. Genus _Sabellaria_. Pl. V.

_Animal._ But slightly differing from the Pectinaria.

_Shell._ Tubes numerous, united in a common mass, composed of agglutinated particles of marine substances, cellular at the base; orifice expanded. Found in the Indian Ocean. Two species.

Sabellaria alveolata. S. crassissima.

3. Genus _Terebella_. Pl. V.

_Animal._ Body tubicular, elongated, cylindrically depressed, attenuated posteriorly; a row of nodulous and setiferous papillæ on each side; numerous filiform, twisted tentacula surrounding the mouth.

_Shell._ An elongated cylindrical and membranous tube with lash-like appendages at the end; covered with adhesions of sand and shells. Inhabits the coast of New Holland. Four species.

Terebella conchilega. T. ventricosa. T. cristata. T. vermicuta.

4. Genus _Amphitrite_. Pl. V.

_Animal._ Body tubicular, elongated, cylindrical, attenuated behind with many annulated segments.

_Shell._ An elongated cylindrical tube growing thinner towards the base, of a tough membranous texture, and generally without adhesions. Mediterranean sea. Seven species.

Amphitrite ventilabra. A. penicilla. A. magnifica. A. vesiculosa. A. volutacornis. A. infundibula. A. minima.

FAMILY IV.

SERPULACEA. Five Genera.

1. Genus _Spirorbis_. Pl. V.

_Animal._ Gills or respiratory organs separated or covered by an operculum.

_Shell._ A testaceous tube turned spirally on a horizontal plane, the lower portion of which is attached to marine substances, generally fuci: opening of the tube terminal, rounded or angular. Found on Algæ on the British coast. Six species.

Spirorbis nautiloidis. S. spirilla. S. tricostalis. S. bicarinata. S. carinata. S. lamellosa.

2. Genus _Serpula_. Pl. V.

_Animal._ Body tubular, elongated, depressed, and attenuated behind; segments numerous and narrow; small bundles of awl-shaped bristles in a single row on each side.

_Shell._ A solid calcareous tube, brown, purple, yellow, tawny, pink, white, or tinged with green. The shells are irregularly twisted, in clusters, and affixed to other substances. Inhabits the coast of Britain. Twenty-six species.

Serpula vermicularis. S. fascicularis. S. intestina. S. contortuplicata. S. plicaria. S. glomerata. S. decussata. S. protensa. S. infundibula. S. annulata. S. cereola. S. filograna. S. vermicella. S. filaria. S. pellucida. S. intorta. S. cristata. S. spirulæa. S. quadrangularis. S. minima. S. echinata. S. sulcata. S. costalis. S. dentifera. S. sipho. S. arenaria.

3. Genus _Vermilia_. Pl. V.

_Animal._ Body tubicular, elongated and attenuated towards the posterior part, and provided superiorly with a simple testaceous orbicular operculum.

_Shell._ A testaceous cylindrical tube, narrowed in the rear, twisted, and adhering by the side to marine substances, aperture round, the margin armed with from one to three teeth. Inhabits the British coast. Nine species.

Vermilia rostrata. V. triquetra. V. bicarinata. V. eruca. V. subcrenata. V. plicifera. V. scabra. V. tæniata. V. plicata.

4. Genus _Galeolaria_. Pl. V.

_Animal._ Distinguished from the vermilia by a very peculiar operculum.

_Shell._ In groups, testaceous, cylindrical, subangular, wavy, adhering by the base, and open at the summit; aperture orbicular, terminated on the side by a spatular tongue; operculum orbicular, squamose, and consisting of from five to nine testaceous parts or valves. Inhabits the Indian seas. Two species.

Galeolaria cæspitosa. G. elongata.

5. Genus _Magilus_. Pl. V.

_Animal._ Unknown.

_Shell._ Usually found imbedded in a species of Madrepore. Base bent into a spiral form, oval, with four contiguous, convex volutions (the last of which is the largest), and prolonged into a straight waved tube, convex above, carinated beneath. Inhabits the sea at the Isle of France. Two species.

Magilus antiquus. M. muricatus.

CLASS II.
CIRRHIPEDA.

_Animal._ Soft, without head or eyes, testaceous, body fixed as if reversed, inarticulated, furnished with a mantle, having above tentacular arms, with curled tufts multiarticulated, mouth beneath, not projecting, dentated transverse jaws disposed in pairs. Number of arms, unequal and varying, disposed in rows, each composed of two rows of curled tufts of bristles; fringed; a corneous skin supported by a pedicle. Medulla longitudinal and knotted; gills external, sometimes concealed; circulation by heart and vessels. One Family.

FAMILY.

CIRRHIPEDA. Ten Genera.

1. Genus _Tubicinella_.

_Animal._ Body inclosed in a shell, with small setaceous and unequal cirri.

_Shell._ Univalve, operculated, tubular, erect, a little attenuated towards the base, bound with annular transverse ribs, truncated at both ends, open at the summit, and closed at the base with a membrane. Operculum with four obtuse valves. South American seas. One species.

Tubicinella balænarum.

2. Genus _Coronula_. Pl. V.

_Animal._ Body seated, enveloped in a shell with small setaceous and cirrous arms.

_Shell._ Sessile, apparently indivisible, suborbicular, conoidal or blunt, conical, the extremities truncated, the sides very thick, the inside hollowed into radiating cells. Operculum composed of four obtuse valves. Inhabits the North seas. Five species.

Coronula diadema. C. testudinaria. C. balænaris. C. pulchra.

C. denticulata.*

3. Genus _Balanus_. Pl. V.

_Animal._ Body sessile, inclosed in an operculated shell; branchiæ numerous, placed in two rows, unequal, articulated, ciliated; each composed of two cirri, supported by a peduncle, and exsertile; mouth with four transverse dentated jaws, with four hairy palpi-like appendages.

_Shell._ Formed of six distinct coronary valves, one dorsal, one ventral, and two pairs of laterals, with a calcareous support; operculum forming a sort of pyramid, by four articulated pieces in the aperture of the shell. Is found in almost all seas. Thirty species.

Balanus angulosus. B. nigrescens. B. roseus. B. amphimorphus. B. crispatus. B. stalaciferus. B. patellaris. B. calycularis. B. subimbricatus. B. palmatus. B. dupluconus. B. semiplicatus. B. lævis. B. punctatus. B. perforatus. B. rugosus. B. latus. B. plicatus. B. galeatus. B. spinosus. B. placianus. B. sulcatus. B. cylindraceus. B. ovularis. B. radiatus. B. fistulosus. B. Lyonsii.

· · · · ·

B. tintinabulus.* B. miser.* B. geniculatus.*

4. Genus _Acasta_. Pl. V.

_Animal._ Body without a peduncle, and inclosed in a multivalve shell, found in sponge or marine bodies, mouth and tentacula placed in the apex, or upper part of the body.

_Shell._ Patella-shaped, sub-conically oval, formed of six lateral unequal valves forming the base, which being convex prevents the shell from standing by itself in an erect position, when detached from the substance which envelopes it. Inhabits the British seas. Four species.

Acasta Montaguii. A. sulcata. A. glans. A. tubulosa.

5. Genus _Creusia_. Pl. V.

_Animal._ Body, subglobular, inclosed in an operculated shell; having three or four pairs of tentacular arms: mouth at the anterior part of the body.

_Shell._ Sessile, fixed, orbicular, conical, consisting of four united unequal valves; attached to madrepore and other marine substances, they are almost microscopic, and found only in the seas of hot countries. Inhabits the China seas. Three species.

Creusia stromia. C. spinulosa. C. verruca.

6. Genus _Pyrgoma_. Pl. V.

_Animal._ As above.

_Shell._ Sessile, univalve, rather globular, ventricose, convex above; apex perforated; aperture small, elliptical, operculum quadrivalve. Inhabits the Indian seas. One species.

Pyrgoma cancellata.

7. Genus _Anatifera_. Pl. V.

_Animal._ Body covered with a shell, supported by a long tubular tendinous peduncle; with long, numerous, and unequal tentacular arms, which are articulated and ciliated, and emanating from the summit on one side.

_Shell._ Compressed on the sides, with five flat valves, the valves contiguous and unequal; the lower lateral ones the largest: the whole of them united and kept together by means of their membranes. Inhabits the British seas. Six species.

Anatifera lævis. A. villosa. A. vitrea. A. dentata. A. striata. A. aculeata.

8. Genus _Pollicipes_. Pl. V.

_Animal._ Body covered by a shell, and supported on a tabular, tendinous, scaly peduncle; with many tentacular arms.

_Shell._ Consisting of thirteen or more valves, the smallest at the sides, which are very flat and compressed, the peduncle short, wrinkled, rigid, and often covered with scales like shagreen. Inhabits the European and American seas. Six species.

Pollicipes cornucopia. P. scalpellum. P. homii. P. mitella. P. peronii.

· · · · ·

P. Mortoni.*

9. Genus _Cineras_. Pl. V.

_Animal._ Body pedunculated, and encased in a membranous tunic, which is swollen above, with an opening below the summit, from which protrude many ciliated articulated arms.

_Shell._ Composed of five testaceous oblong valves, two at the sides of the aperture and three on the back, not covering the whole of the body; supported by a peduncle of a greenish colour with several longitudinal stripes. Inhabits the British coast. One species.

Cineras vittata.

10. Genus _Otion_. Pl. V.

_Animal._ Body pedunculated, enveloped in a membranous tunic, which is ventricose above; two horn-like tubes, directed backwards, truncated, and open at their points, and situated in the apex of the tunic; having a lateral opening, with many articulated and ciliated arms.

_Shell._ Composed of two testaceous valves, attached near the lateral opening, the centre aperture admitting the animal’s tentaculæ, the singular form of which prevents its being blended with the genus cineras without a further examination of its structure. Inhabits the North seas. Two species.

Otion Cuvieri. O. Blainvillii.

CLASS III.
CONCHIFERA.