themselves under its protection. In the different species | of the mantle, and lies upon the back of the animal. of Snail a Slug, all agreeing closely in general structure, every variety of this kind may be seen. In some of the more slender and flexible species even this is nearly wanting; all that remains of a shell in the Loligo (Squid) being a narrow horny plate, somewhat resembling a feather in shape, whence it is termed th In the headless Molluscs, on the other hand, we find two very gistinct groups; in the first of which the shell is constantly present, while in the second it is as inva-pen. riably absent The general structure of the latter is much inferior to that of the shell-bearing class, and it approaches more nearly in several of its characters to the Polypifera. The highest class of Acephalous Molluscs is named CONCHIFERA, from the constant occurrence of a shell, which is nearly always formed of two pieces, or bivalve. The lowest is denominated TUNICATA, the shell being replaced, as it were, by a leathery or cartilaginous envelope or tunic, which encloses the whole body CLASS XIV.-CEPHALOPODA. The class of Cephalopoda, which is so named from the arrangement of the feet or locomotive organs around the head, must be regarded as the highest among the Mollusca in respect to the complexity of its organization, and it is the one which approaches most nearly to verleviated animals. In the general form of their bodies, and in their adaptation to a rapid motion through the water, many species bear a considerable resemblance to Fishes, and are, indeed, commonly reputed as such. The name of the class expresses the character which distinguishes it from all others. On the head, which is furnished with eyes resembling those of higher animals, and also with organs of hearing, and perhaps also of smell, are disposed in a circular manner the curious apendages, which have received the names of feet or arms, and to which either terin may be justly given, as they are organs of prehension as well as of locomotion. These are usually eight or ten in number; but in the true Nautilus they are much more numerous, amounting to nearly a hundred. The mouth, which is situated in the centre of the circle of arms, is provided with a pair of firm horny mandibles or jaws, of which one is sharply pointed, and overlaps the other when closed, so that the whole very much resembles the bill of a parrot. This beak encloses a large fleshy tongue, roughened with horny prickles; and the œsophagus leads to a muscular stomach, which much resembles the gizzard of birds. All the Cephalopoda are aquatic, and consequently breathe by gills. These are disposed symmetrically on the two sides, and are covered in by the mantle. This envelope includes the whole body, but there is an opening in which it gives passage to the head. Through this opening the water enters to the gills, and it is expelled through a tubular prolongation of the mantle termed the funnel, which also serves as the excretory canal for other fluids. Most of the Cephalopoda possess something analogous to the shells of other Mollusca, although it often exists in a form and position which might almost prevent its being recognised as such. The only species at present known in which the body of the animal is enclosed within it, as in the shells of Gasteropoda, are the Nautilus and the Argonauta (Paper-Nautilus). In the former of these the shell is spiral, and is divided by transverse partitions into cambers, in the last or outermost of which the animal lives; and, when it wishes to enlarge its shell, it prolongs the mouth of it, which widens as it is prolonged, and throws a new partition across the bottom. The shell of the Argonaut has no such chambers, and the animal, when hiding within it, occupies the whole of its cavity. In the common Sepia (CuttleFish), on the other hand, the shell is reduced to the form of an oval plate, commonly known as the cuttle-fish bone, from which pounce is derived, that may be picked up on almost every shore; and this is enclosed within a fold The arms of all the Cephalopoda are covered with very curiously constructed suckers, by which they are enabled to take firm hold of any thing to which they are applied These act by excluding the air, and thus producing a vacuum, exactly upon the principle of the boy's leather | sucker. In this manner they are enabled to master animals which it would have been supposed entirely out of the power of their soft unprotected bodies to combat successfully. They are generally agile as well as voracious; and prey upon almost all other classes of marine animals. Their special articles of food, however, are Fishes and Crustacea; and they are probably the only animals which are able to restrain the inordinate multiplication of the larger members of the latter class. The firm armour of the crab or lobster, and its powerful claws, are no protection to it against these soft-limbed cuttle-fish, which wind their arms round their bodies, and, fixing every part by means of their suckers, tear apart the divisions of the shell by means of their hard parrot-like bills. So firmly do these suckers adhere, that, while the muscular fibres remain contracted, it is easier to tear away the substance of the limb than to release it from its attachment. The Cephalopoda which are unprotected by an exter. nal shell, are furnished with a curious means of escaping from their enemies. This is the secretion of a dark fluid, which, when emitted by the animal, tinges the water around to such a degree that it can escape in the cloud it has made. The fluid is usually stored up in a bag communicating with the funnel through which it is ejected under the influence of alarm. This ink-bag, as it is termed, is collected from the species inhabiting the Indian seas; the ink forms a valuable pigment, known to the artist as sepia, the name of the animal which furnishes it. The class of Cephalopoda may be subdivided into two orders. In the higher division, which approaches the nearest to vertebrate animals, the branchia or gills are two in number, and the order is termed DIBRANCHIATA, while in the one most closely allied to the Gasteropod Mollusca, the branchiæ are four in number, and the order is therefore termed TETRABRANCHIATA. Order I.-Dibranchiata. The Dibranchriate order includes all the best-known forms of the class. It is divided into two tribes, in one of which there are but eight arms, while in the other there are ten, of which, however, two are different from the rest. The first of these, termed OcтOPODA, may be considered as the highest in point of general organization; the second, termed DECAPODA, presents many points of approach to the Tetrabranchiate order, both in the increased number of arms, and in the presence of an inner circle of short tentacula, as well as in several internal characters. The Sepia, or common Cuttle-Fish, is a characteristic example of the DECAPOD family. Some species of it abound in almost all seas. It has two long slender arms, which are furnished with suckers only at their extremities; and by these the animal is said to fix itself, as by anchors, when exposed to a rough sea or strong current. They are probably employed also in seizing prey, which is brought by them within the range of the others. To this group we are probably to refer the Spirula, a little chambered shell, the animal of which is very imperfectly known; and a large number of fossil chambered shells, known as Ammonites, Belemnites, &c.; the animal of which was probably analogous to the Supia, including the shell, like the bone of the cuttle-fish, within the body. The OCTOPODS, which form the highest family of the Dibranchiata, have but eight arms, without tentacula; and they are destitute of lateral fins, so that they depend entirely upon the arms for their movement through the water. Accordingly it is found that these are very large and powerful, and that the body is proportionally short. The arms are generally united at their bases into a kind of circular fin, by the motion of which the animal can swim backwards with great energy. The common Octopus, or Poulp, of European shores, has the arms six times the length of the body, and each furnished with 120 pairs of suckers. It can leave the water, and creep over the beach; taking hold of the ground before it by the extension of its arms, and then dragging the body towards the point at which the suckers are attached. A very interesting species of the Octopod group is the Argonauta Argo, commonly called the Paper-Nautilus, from the whiteness and delicacy of its shell. As the animal has little in common with the true Nautilus, it would be much better if the latter designation were entirely abandoned, and the term Argonaut substituted for it. The shell is not chambered, but possesses one spiral cavity, into which the animal can withdraw itself entirely; this, however, has no muscular attachment to it, whence it has been supposed by many naturalists that it was only a parasitic inhabitant, which had taken up its abode within it, and that the shell, from its resemblance to that of Carinaria, was formed by a Gasteropod mollusc allied to that genus. It has been lately proved, however, by the interesting experiments of Madame Power, that the shell increases regularly with the growth of the animal, which possesses the power of repairing it when injured; so that no doubt can exist that the Argonaut is the original constructor of it. Of the eight arms of the Argonaut, six taper gradually towards the extremities; but two are expanded into wide membranous flaps. From very early times, this animal has been reputed to swim on the surface of the water, using its arms as oars, and spreading these expanded Shen Argonaut, with animal in the reputed position. membranes as sails to the wind. But it is now known, by accurate observation of the living animal, that this is altogether a fiction (though an interesting one); and that the expanded arms are spread over the sides of the shell, meeting along its keel or edge, and almost completely enclosing it. It is by these, indeed, rather than by the surface of the body itself, that the calcareous secretion is poured out for the enlargement or separation of the shell. By the action of the arms, the Argonaut wims backwards in the same manner as other Octopi; and it can also creep along the bottom of the sea. Order II.-Tetrabranchiata. From the remains preserved in a fossil state, the Tetrabranchiata appear to have formerly abounded in our seas; but the only living representative of them is the Pearly Nautilus (N. Pompilius). In the anima. which forms and inhabits the well-known chambered shell found on most tropical shores, we observe many differences from the usual type of organization in the Cephalopods. The arms are very numerous, amounting to nearly a hundred; they are unprovided with suckers; and they are short and slender, resembling closely the tentacula of many Gasteropods. The head of the Nautilus supports a large fleshy disc, upon which it is believed that the animal crawls upon the bottom or sides of the ocean, as a snail upon its foot. The animal frequents deep waters; and, though it is occasionally found at the surface, it sinks upon the least alarm, so that it has been very rarely captured, although the empty shell is so common. This power of rising and falling in the water appears in some degree connected with the structure of the shell, and with the mode in which its chambers communicate with the body by a membranous tube which passes through all the partitions, and is called the siphuncle. But of the mode in which this operates no very satisfactory account has yet been given.* A large number of fossil shells, analogous to that of the Nautilus, and hence called nautilites, are found in various strata, from the oldest limestones and sandstones of the Silurian system, to those covering the chalk. CLASS XV-PTEROPODA. The Pteropoda are a small but remarkable class of Mollusca, distinguished by the adaptation of their structure for active locomotion in water only. Their general organization is higher than that of the Gasteropods; and they are particularly distinguished by the possession of a pair of fin-like organs, which are attached to the anterior part of the body, and are evidently adapted for propelling it rapidly through the water. The body is uniformly symmetrical; that is, its two sides precisely correspond-a condition obviously favourable for rapid movement. It is from the wing-like character of these lateral appendages that the name of the class is derived. The dimensions of the animals composing this class are uniformly small; but the number of individuals which associate together in shoals is often enormous, so that the sea appears literally alive with them. Some of them are possessed of a shell, whilst others are unprovided with such a protection. Wherever it exists it is very light and delicate; and it seldom covers more than the posterior part of the body. In one beautiful little Mollusc, the Cymbulia, it is of a slipper form, the wings or fins issuing from the large opening. The head is usually prominent, possessing eyes and sensitive tentacula; and the interior organization is of very complex nature. One of the best-known genera of this group is the Clio, which abounds both in the arctic and antarctic seas, and is a very important article of food to the whale. idea of that of the whole class. The Clio is itself emiThe aspect of this animal will convey a good general nently carnivorous, and in its whole organization is fitted to seize and prey upon the yet more minute inhabitants of the deep. The Clio Lorealis is well known to the whale-fishers and others as whale's food; this species swarms in the arctic seas, and when the weather is calm, these little face. According to Cuvier, the sea is sometimes so animals may be seen floating in myriads upon the surglutted with them, that the whales cannot open their See Dr. Buckland's Bridgewater Treatise for an attempt at explanation. This is deficient in its application to all those cases in which the siphuncle is a shelly not a membranous tube, as in the Spirula, Ammonite, &c mouths without engulfing thousands of these small | but those which appear most widely separated may be molluscs. An analogous species, the C. Australis, ap Clio Borealis. shown to be connected by intermediate links. The open cone of the Limpet may be regarded as one of the simplest forms; in an allied genus, the Pileopsis, we find the point prolonged, and somewhat rolled upon itself; and by various links of this kind, we are brought to the regular spiral of the snail. From this we may return to the long straight form by the Scalaria, in which the coils of the spire touch each other only by their ribs; and by the Vermetus and Magilus, in which the commencement only of the shell possesses a spiral form, the remainder being prolonged into a straight tube. When the shell is spiral, and the point and mouth are not in the same pears equally abundant in the polar regions of the plane, a sort of central pillar is formed, like that round southern hemisphere. CLASS XVI.-GASTEROPODA. It is in the animals of this class that we find the characters of the Mollusca most prominently displayed, namely, the high development of the nutritive apparatus, with very feeble powers of locomotion. In all the more perfect forms, which are usually carnivorous, a distinct and prominent head exists, furnished not only with tentacula, or feelers, but also with eyes, and with what appear to be rudiments or organs of smell and hearing. In this part, we usually perceive that symmetry or correspondence between the two halves, which has been spoken of as characterizing the animal organs in general; whilst in the posterior part of the body, which is made up of the organs of vegetative life, this symmetry is seldom to be discerned. They have the power of crawling from one place to another, by means of the expanded muscular disc or foot with which they are furnished; and as this foot proceeds from the belly or under surface of the animal, the class receives the name given to it. The mode in which it is used may be well seen by placing a snail or slug on a piece of glass, and looking at it from the under side. Many of those which inhabit the water can swim with considerable rapidity; but this power is chiefly possessed by those species which have no shell, or but a very slight one, and can bend their bodies in any direction. The general character of the shelly structure, where it exists, is the same as in the Conchifera. It is in general composed of one piece, and called a univalve; in some instances, however, it is a multivalve and in many species there is a small operculum or lid to the mouth of the shell, which may in some degree be regarded in the light of a second valve. The body is attached to the interior of the shell by muscles which can withdraw it or project it at the will of the animal; and the operculum can be drawn down upon the mouth with considerable force. It is the habit of some species (as the Limpet and Haliotis) to attach themselves, by the expanded surface of the foot, to rocks, &c.; these are able to draw the shell closely down upon the rock, with great muscular power, just as the Conchifera draw together their valves; a short interval existing, however, when the animal is not alarmed, for the admission of water or air to the cavity of the shell. A very slight irritation will cause the animal to draw the shell close down on the rock, from which it is then very difficult to detach it. The shell is formed, as in other Mollusca, by an exudaion from the mantle; and is enlarged at intervals, in accordance with the increasing size of the animal. In some, the addition of an entire new interior layer, projecting beyond the old one, is made at every such period, as in the Conchifera; but in others the new matter is secreted only at the edge of the previous shell, and is joined on, as it were, to it; in these the line of addition is usually marked by a prominent rib on the exterior, but the interior is beautifully smoothed off. The forms of the shell in this class vary extremely; which a spiral staircase is constructed. This is called the columella: and it is usually grooved at its lower part, for the passage of water to the respiratory organs, which are placed within the shell. The margin of the shell is not unfrequently fringed with spines, as in the Murex; these are formed, ke similar appendages in the Conchifera, by prolongations of the mantle; and the dissimilar number of them in different specimens has caused the establishment of many species, which, now that the habits of the animal are better known, prove to be but different forms of the same. For it has been ascertained that the animal has not only the power of forming new spines, but of removing old ones, especially such as would interfere with the continued growth of the shell. The edge of the mantle is applied against their bases, and a kind of absorption of shelly matter seem to take place-a notch being formed, which causes them to be easily broken off. Various analogous changes are produced by a similar action in other shells. the portions first formed being wholly or partially removed. Sometimes the walls of the older portion are thinned, for the purpose of lightening the shell; and in other cases the top of the cone is altogether removed, a groove having been formed around its interior, which renders it so weak as to be easily broken off: in these last cases, the animal previously withdraws itself from the part that is thus to be separated, and throws a new partition across, by which the top of the shell remains closed after the division. A shell thus deprived of its apex is said to be decollated. Murex Tenuispina It is not only by such removals that the form of univalve shells undergoes a great change. Sometimes additions are made to them, which completely alter their figure, so that two individuals of different ages would be scarcely supposed at first sight to belong to the same tribe But in all these cases the form of the young shell may be traced in that of the adult. The preceding figures of the Pteroceras show this change in a moderate degree; in other genera it is much more remarkable. In another group of shells, of which the common Cowry is an example, a still more curious alteration takes place. In the Young Shell. Adult Shell. Pteroceras Scorpio. young shell the edge is sharp, and the mouth or opening of considerable breadth. This state continues as long as the shell is increasing in size; but when it has arrived at adult age, the outer lip is thickened, and brought so near the other as to leave but a narrow chink between them. At the same time, a prolongation of the mantle on each side deposits a new layer of shelly matter on the outside of the previous one; and as the two prolongations meet along the back (the line of their junction being usually evident on the shell), this additional coat, which is very hard and porcellanous in its texture, encloses the whole Previous shell. Young Shell. Adult Shell. Cypræa Exanthema. The operculum is principally confined to the aquatic Gasteropoda. It is sometimes of the same texture as the shell itself, and sometimes horny. It does not always close the entire mouth of the shell, but it is sometimes made to fit it, at all stages of growth, with the most beautiful accuracy. Some of the land species also possess an operculum; but in general they are destitute of it, and they form during hybernation a temporary closure to the mouth.of the shell by a viscid secretion, which hardens into a thin plate, and includes within it a bubble of air. Behind this, a second and even a third similar partition is occasionally found, as in the common snail. The subdivision of this extensive class into orders, may be best affected by arranging the different tribes ac cording to the character and position of the respiratory organs. The following are those adopted by Cuvier 1. PULMONIA. These are terrestrial species, adapten to breathe the air by means of a pulmonary sac or aircavity, the orifice of which they can open or close at will. Many have no shell. 2. NUDIBRANCHIATA. These, as well as all the suc ceeding orders, are aquatic, being adapted to respire water by gills, like other Mollusca. The animals of this order have no shell, and they carry their branchia, which present various forms, on some part of the back. 3. INFEROBRANCHIATA. These are similar in many respects to the preceding, but the branchia are situated under the margins of the mantle. 4. TECTIBRANCHIATA. In the greater part of the animals contained in this order, the branchiæ are situated upon the back or on the side, and are covered in by a fold of the mantle, and this fold usually includes a shell more or less developed. 5. HETEROPODA. This is a small order, characterized by the peculiar form of the foot, which is not spread out horizontally, but compressed vertically into a sort of fin. They carry their branchiæ, the tufts of which are generally protected by a shell, upon the back. 6. PECTINI BRANCHIATA. The animals of this order, to which belong all the spiral shells, except those of the Pulmonea, are so named from the comb-like form of their gills, which are usually situated in a cavity behind the head, corresponding with the respiratory sac of the Pulmonea. This is by far the most numerous order of the whole. 7. TUBULIBRANCHIATA. These have many affinities with the last order, but the shell is spiral only at its apex, where it is commonly fixed to (or rather enclosed by) other bodies, and is prolonged in the shape of a tube more or less regular. 8. SCUTIBRANCHIATA. In these, also, there is a considerable resemblance to the Pectinibranchiata in the form and position of the gills; but the shells are very open, scarcely in any degree spiral, and cover the body and gills like a shield; and they also differ essentially in their mode of reproduction. 9. CYCLOBRANCHIATA. These molluscs have their gills disposed in little tufts under the margins of the mantle, much as in the Inferobranchiata; but they have shelle which are spread out over the body, and differ from that order in the mode of reproduction. Order I.-Pulmonea. Although the greater part of the Molluscs of this order live on land, some are aquatic; but these, like the aquatic air-breathing Insects and Vertebrata, are obliged to come occasionally to the surface to breathe. They all feed chiefly upon vegetables, and many of them exclusively so; but some are extremely voracious, and will devour almost any organized matter that falls in their way. They are diffused through all climates, particular species being restricted to each. Those without a shell, commonly known as Slugs, constitute the family LIMACINE. In the common Slugs, as in most of the terrestrial species of this order, we observe a prominent head, with four tentacula, and at the end of the longer pair the eyes are situated. These tentacula can be drawn inwards, by a process resembling the inversion of the finger of a glove. On the back there is a kind of shield or disc formed by the mantle, which sometimes encloses a small shell. This shield covers the pulmonary sac, the opening of which is on its right side, and the head can be withdrawn beneath it. The Testucella is a kind of slug which has the disc of the mantle at the posterior extremity, and this always contains a small shell. This animal, which feeds largely on earth-worms, is abundant in the south of France, and has lately been introduced into the gardens of this country, where it is multiplying rapidly. The Snails and their allies, constituting the family HELICINE, are closely allied to the Slugs in organization; differing in but little else than the possession of a shell imto which the body may be withdrawn. The common garden-snail of this country, and the Helix pomatia, or edible snail of France and Italy, are well-known examples of this family. More striking ones are to be found, however, in tropical climates; where some species of the genus Bulimus attain to great size, the eggs being as large as a pigeon's. In some species the direction of the coils of the shell is opposite to what it is in other spiral shells; such are said to be reversed. A European species of this genus is one most remarkable for the decollation of its shell. Another large snail of tropical climates, as the Achatina, which feeds on trees and shrubs, chiefly on the western coast of Africa, and in the West Indies. Several of its species are distinguished by the beauty of their colours. The aquatic Pulmonea have only two tentacula. From the necessity of coming to the surface to breathe, they can only live in water of inconsiderable depth; and they chiefly inhabit ponds and shallow streams, or the banks of rivers. Some, however, live on the sea-shore. The Planorbis, the shell of which is quite flat, having all its coils upon the same level, is a very common genus in this country; as is also the Lymnaea, which feeds upon seeds, as well as the softer parts of plants, and the stomach of which has a very muscular gizzard. Order II.-Nudibranchiata. The animals of this order, which might be designated Sea-Slugs, are all marine; and being adapted to breathe water at any depths, and also, in many instances, to swim with facility, they are often found at a great distance from land. When they swim it is usually in a reversed position, the foot being turned upwards; this is made concave by muscular action, so as to serve as a kind of boat, the buoyancy of which keeps the animal at the surface without effort. This order is a very numerous one, and some of its species attain a considerable size; but, from their habits, little is known of them. Order III.-Inferobranchiata. The few Molluscs contained in this order differ but little from the last, except in the position of their gills, and their incapability of swimming. They are, therefore, confined to the sea-shore; where they subsist, as do the Nudibranchiata, upon sea-weeds and other aquatic plants. Order IV.-Tectibranchiata. This order begins to show an approximation towards that disposition of the gills which characterizes the great bulk of the class; the animals composing it are marine, and live chiefly on the shore or on floating sea-weeds. A very characteristic example of the order is the Aplysia, commonly termed Sea-Hare, which is abundant on many parts of the British coasts. Its vernacular name is probably derived from the peculiar form of the superior pair of tentacula, which are flattened and hollowed, like the ears of a quadruped. The head has a very distinct neck. The branchia consists of leaflets arranged in a complex form, and situated on the back, beneath a fold of the mantle, which also encloses a flat horny shell. The digestive apparatus is very complicated; consisting of a meinbranous crop like that of birds, a gizzard having cartilaginous walls, and a third stomach beset with sharp hooks in its interior. These animals feed on sea-weed. They are very sluggish in their movements; but have a peculiar means of defence, consisting of a deep purple liquid, which they can discharge from the edge of the mantle when alarmed, and by which the surrounding water is discoloured, so that they cannot be discerned. Order V.-Heteropoda. This is a very small order; but the animals contained in it differ remarkably from al. other molluscs. At the edge of the vertical muscular plate, which has been mentioned as occupying the position of the foot in the other Gasteropoda, is a small conical sucker, by which the animal can attach itself, and which represents the expanded disc of other orders. The gills are placed on the back, and close behind them are the heart and liver, which seem, as it were, external to the body. In one of the few genera which the order contains, these parts are protected by a small shell, whilst in another there is none. The body, consisting of a semi-transparent gelatinous substance, enclosed in a muscular envelope, is elongated, and generally terminated by a compressed tail; this body can be distended with water. The animal swims in a reversed position, the fin-like foot being uppermost, and the shell depending below. They are limited to warm latitudes : one species of the Carinaria inhabits the Mediterranean, and occasionally appears on particular coasts in large. numbers; whilst others are peculiar to the tropics, where most of the allied genera also exist. The shell of the Carinaria is interesting, on account both of its extreme delicacy and fragility, and on account of the strong resemblance which that of the Argonaut or Paper-Nautilus bears to it. Order VI.-Tectinibranchiata. This order is not only by far the most numerous in the whole class, but contains the animals which may be regarded as its most characteristic examples. They have all two tentacula and two eyes, sometimes raised on stalks, as in the snail. The mouth is prolonged into a sort of proboscis; and the tongue is furnished with little hooks or recurved spines, which enable it to wear down the hardest bodies by slow and oft-repeated action. The cavity in which the gills are fixed occupies the last whorl of the shell; and in some of the order there is a tubular prolongation of the mantle, termed the siphon, for the purpose of conveying water into this cavity, so that the animal can breathe without leaving its shelter. By the presence or absence of this organ, and by the form of the shell, which here appears to bear a sufficiently constant relation with that of the animals, this large group may be arranged under the following families:-1. TROCHOIDE, in which there is no siphon, and which have the mouth closed by an operculum. Of this the common periwinkle is a characteristic example, though very small in proportion to tropical species. 2. CAPULOIDE, which have a wide open shell, very much like that of the limpets, without operculum or notch at the margin for the passage of a siphon. 3. BUCCINOIDE, which have a spiral shell, and a canal at the end of the columella for the passage of the siphon; this is sometimes extremely prolonged, as in the Murex; and the genera exhibiting this character are all carnivorous in their habits. To this family belon the animals forming the greatest number of marine uni valve shells preserved in cabinets. Order VII.-Tubulibranchiata. The Molluscs of this order construct an irregulariy tubular shell, which so much resembles that formed by certain Annelida, as to be scarcely distinguishable from it. They are very few in number. Order VIII.-Scutibranchiata. This order is also a small one, containing but two principal genera, which do not differ widely from the impets, except in the disposition of the gills. The shells number are not in any degree spiral. are very open, without an operculum, and the greater In the Haliotis, the shell is slightly twisted; and from a faint resemblance it is thought to bear to the ear of a quadruped, it has been called the Sea-Ear. This animal, in its living state, is one of the most beautiful of Gasteropods, on account of the variety and richness of its colours. Its shell, when the surface is polished, possesses a pearly lustre, with resplendent metallic hues. It is consequently much ht for as an ornament. |