separation, which is hereafter made of some shells, which originally were in the genus Helix, in agreement with the ideas of Brugulere, will be, therefore, more cor

rect.

Volvaria, a cylindrical shell, twisted on itself, without a projecting spire; the opening narrow, as long as the shell; one or more folds on the base of the columel. la. This genus was formed by Lamarck, from a shell which is figured and describ. ed by Pennant, vol. iv. Plate LXX fig. 85 He considers it as an intermediate between Bulla and Bulima.

Bulla. A tumid shell, the spire not projecting; the opening as long as the shell; no umbilicus. This genus of Linnæus has been much reduced by Brugulere, who placed several species under Bulima, and established his genus Ovula. Lamarck has still further reduced them, by forming the genera Terebellum, Pyrula, Ampulla, and Achatina.

Ianthina. This genus is formed by Lamarck on a single shell described by Lister, Brown, Forskal, and other naturalists; which derives its claims of distinction from Helix, not so much from the character of the shell as from that of the animal, which differs in its structure materially from the animal of the Helix, since it is furnished with a curious apparatus, being an inhabitant of the sea, for swimming, instead of that for crawling, with which the Helices are provided. It is nearly globular, and almost diaphanous; the opening is nearly triangular, with an angular sinus at the right edge.

Turritella. This genus was formed by Lamarck for the reception of those shells which Linnæus had placed in the last section of his genus Turbo, as Towers; and which Dargenville and Favanne had considered as screws. The characters of the genus are, a turriculated shell; the opening round, whole, but having a sinus' at the right edge.

Cyclostoma. This genus was formed by Lamarck for the reception of the Wentletrap, and other shells of the same character. The propriety of thus forming a new genus is rendered evident, by the doubts which had arisen respecting the placing of it in any old genus. Linnæus having considered it a Turbo; Rumphius, a Buccinum; Dargenville, a Screw; and Davila, Gualteri, Guettard, and Favanne, merely a Tube, from its not possessing a columella, which they considered as essential in a univalve shell. The shells of this genus differ in their forms;

their openings are nearly round, and their sides connected circularly. The shell is formed of seven spires, separated by a void space; with ten or twelve longitudinal ribs, which, uniting, form a rim round the lip These ribs externally sup ply the place of a columella.

Bulimus. A globular, oval, or turricu lated shell, the opening of which is entire, not grooved at the base, and always longer than wide This genus of Bruguiere comprises some of the shells considered by Linnæus as Helices and Bulle; and the genera Auricula, Pyramidella, Melania, Lymnæa, Agathina, Maillot, and Bulima, of Lamarck. The essential character distinguishing this genus from Helix is the opening being longer than it is wide.

Turbo. A conoidal or turriculated shell; the opening entire, round, without any tooth; the edges disjoined on the superior part. Several shells, which were reckoned by Linneus of this genus, have been removed from it by Brugutere, and placed under his genus Bulima, and others have been taken from it by Lamarck, and disposed under the genera Cyclostoma and Turritella.

Trochus. A conical univalve shell: the opening almost always quadrangular flattened transversely; the columella oblique. Lamarck has divided this genus into four: 1. Trochus. 2. Solarium, with an open umbilicus, or crenulated opening on the inside of the spiral turnings, as in the Trochus perspectivus. 3. Monodenta. The opening rounded, and furnished with a tooth, formed by the truncated and projecting base of the columella, as in Trochus labio, Linnæus. 4. Pyramidella: the columella project. ing, perforated at its base, and possessing three transverse folds, as in Trochus do. labratus, Linnæus.

Cerithium. A univalve turriculated shell, the opening terminated at its base by a short, narrow canal, either suddenly turning backwards or truncated, but never grooved out. In this genus of Brugulere are comprehended several shells from the genera Trochus, Strombus, and Murex of Linnæus. The shells differ from those of the Murex by their turriculated form; and from the screws, in not having the groove at the base of the canal.

Pyrula. A subpyriform shell, canaliculated at its base; without any projections, and having the belly part nearer

to its summit than to its base; the spire short; the columella smooth; the right edge without a groove Lamarck, founding the distinction on the situation of the bellied part of the shell, and on the greater or less length of the spire, has formed two new genera; one with those shells possessing this character of the genus Bulla, and the other of the genus Murex, calling the former Pyrula, and the latter Fusus.

Murex An oval or elongated univalve shell, generally foliated, plaited, spinous, or tuberculated; the opening always prolonged into a canal, running straight, or turning directly backwards, and always entire. In the earlier stages of their growth it is difficult to separate the Murices from the Strombi. Lamarck divides this genus of Linnæus into five genera. 1. Murex, with tuberculated or spinous projections, and channelled at the base, as M. ramosus. 2. Fusus; fusiform, without projections, with the bellied part either equally distant from the extremities or nearest to the base; spire elongated; columella smooth; right edge without groove, as M. colus. 3. Fasciolaria; nearly fusiform; no projections; with two or three very oblique folds on the columella and channelled at the base, as in M. tulipa. 4. Pleurotoma: fusiform or turriculated, without projections, and having a groove, or sinus, near the summit of the right edge, as in M. babylonicus. 5 Cerithium, already de

scribed.

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Rostellaria. Lamarck has formed this genus on Strombus fusus (Linnæus,) and on some fossil species found at Courtag non. The characters of the genus are a fusiform shell, terminating inferiorly by a canal with a pointed beak; the right edge entire or dentated; dilated more or less in a wing, according to age, and having a sinus contiguous to the canal.

Strombus. A bellied univalve, terminating, at its base, by a canal, accompa nied with a distinct sinus; the right lip dilating, or spreading itself out, with age, in a simple or digitated lobe Lamarck divides the genus Strombus of Linnæus into three. 1. Strombus; terminating in a short canal, truncated or grooved out; the right edge dilating, with age, into a simple entire wing or lobe; with a sinus distinct from the groove at the base, as in S. pugilis. 2 Pterocera; a bellied shell, terminated inferiorly by an elongated ca. nal; the right edge dilating, with age, into a digitated wing, and having a sinus near

its base, as in S. lambus. S. Rostellaria, the genus last described.

Buccinum. An oblong or oval shell, the opening of which is terminated at the base by an oblique groove, without any sensible canal, or external border. Brugulere has divided the Buccina of Linnæus into the genera Buccinum, Terebra, Cassidæa, and Purpura. Under the genus Buccinum are therefore here comprised tumid shells, with from three to ten spiral turns; a summit generally flattish; a surface rarely even the predominating colours dull; the lip extended more or less in a bow, and rarely jagged.

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Cassidæa. A tumid shell, the opening longer than wide, terminated at its base by a short canal, recurved towards the back of the shell; the columella plaited in the lower part. This genus of Brugulere is intended to comprise the helmets (casques) of Gualteri, Klein, and others.

Terebra. A turriculated univalve; the opening grooved in the lower part: the base of the columella twisted or oblique.

Purpura An oval shell, generally with spines, or tuberculated; the opening terminating in a very short canal, the extre mity of the canal grooved out, the base of the columella finishing in a point. The shells included in this genus by Bruguìere are not those species which have been hitherto considered as Purpuræ, by Dargenville and others, and which belong to the genus Murex; but those species which appear to connect the genus Buccinum and Murex. The opening of these shells is rather large, oval, round, upwards, and more contracted in the inferior part: the right lip has but little thickness, and is grooved or notched; the left expands with a wrinkled ridge, which terminates in the groove.

Voluta. A cylindrical, or oval, univalve shell, grooved out at the base, but without a gutter; the opening longer than wide; and the columella plaited. The division of this genus by Linnæus is very clear and useful; but Lamarck proposes a still nicer distinction of the shells of this genus, by dividing them into eight genera. 1. Voluta, an oval shell, more or less bellied, summit obtuse or mammillated; the base grooved, but without a gutter; the columella with several plaits, of which the lowest are largest and longest; as in voluta musica 2. Oliva, sub cylindrical, grooved at the base; the turns of the spire separated by a channel; the columella striated obliquely, as in Voluta oliva. 3. Ancilla, oblong, a short

spire, base of the opening hardly grooved; a swelling, or oblique roll, at the base of the columella. 4. Mitra, fusiform or turriculated, spire pointed at the sum. mit, the base grooved out, without a gutter; the columella with plaits, the lowest being the least, as in Voluta episcopalis. 5. Columbella, marked by a swelling on the internal face of the right edge, as in Voluta mercatoria. 6. Marginella, the right edge emarginated, as in Voluta vespertilio. 7. Cancellaria, the right edge grooved internally; and the base of the opening almost entire, as in Voluta reticulata. 8. Turbinella, sub-turbinated, canaliculated at its base, with transverse plaits on the columella

Ovula. A tumid shell, more or less elongated at the extremities; the edges rolled inwards; the opening longitudinal, not dentated on the left side. This genus is formed by Lamarck from shells, which had been comprised by Linnæus in his genus Bulla. The shells of the genus Ovula differ from those of Cypræa, chiefly by the absence of teeth from the left side. Bulla volva, ovum, spelta, verrucosa, and gibbosa, of Linnæus, are placed under this genus.

Terebellum, a shell nearly cylindrical, pointed at the summit; the opening longitudinal, narrow upwards, and hollowed out at its base; the columella truncated. This genus is formed, by Lamarck, of the Bulla terebellum of Linnæus, which he has removed from the genus Bulla, and has placed in this genus, as in termediate between the Ovula and the Olives.

Cypræa. A convex, univalve shell, the edges turned inwards: the opening long and narrow, and toothed on each side. The shells of this genus are so distinctly characterized, as to have escaped that confusion which has taken place in many other genera.

Conus. A conical, convoluted univalve; the opening of the length of the shell; linear, without teeth, and hollowed out at the top; the columella smooth. The generic characters are here so determinate, as not to have left any opportunity for changing the acceptation of this genus, as established by Linnæus.

Vermicularia. A tubular shell, twisted in an irregular spiral, in general adhering to some body, and furnished with an operculated opening. The shells with which Lamarck has formed this genus were blended by Linnæus with the Serpule; but the animals which inhabit these shells are very different from the Tere

brelle, which are the only inhabitants of the true Serpulæ.

Silicaria. A tubular shell, spirally convoluted, and laterally divided through its whole length by a narrow fissure; the mouth roundish. Linnæus himself considers it as doubtful whether the shell which forms this genus (Serpula anguina) should be placed under the genus Serpula, or not; but Brugulere, Lamarck, and Daudin, have thought it necessary to establish for it this new genus.

Penicellus. A long tubular conical shell, the superior extremity closed by a disk, beset with numerous short tubes, and surrounded by a projecting coronet; the inferior extremity having been fixed to some solid body. Linnæus had doubted whether the shell, of which Bruguìere has formed this genus, ought not to be placed under the genus Teredo, rather than under that of Serpula, where, however, he left it.

Nautilus. A spiral and nearly discoidal shell, the last turn of which envelopes the rest, and the sides of which are smooth: numerous chambers, formed by transverse smooth septa, perforated by a tube. This genus is divided by Lamarck into three. 1. Nautilus, 2. Spirula, 3. Orthocera.

Orbulites. A spiral, and nearly discoidal shell, the last spire enveloping the rest; the sides articulated by winding sutures; the transverse septæ being pierced by a marginal tube. The shells which Lamarck has assumed for this genus have been hitherto confounded with the Ammonites; they are only known as fossils and as casts.

Ammonites. A discoidal spiral shell, the turns contiguous and all visible, the sides articulated by foliated sutures, and the transverse septæ terminating in winding processes, and pierced by a marginal tube. These, like the shells of the preceding genus, are only with certainty

known to exist as fossils.

Planulites. A discoidal spiral shell, with contiguous and visible turns, with smooth sides, and transverse septæ, not foliated. These shells are supposed to bear the same relationship to the Ammonites as the Nautili do to the Ammonites; but the difference between them and the Ammonites is so little as must often be with difficulty discoverable.

Camerina. A shell with a single valve, without any external spire, the internal part divided into numerous chambers by imperforated septa. This genus was formed by Bruguiere, for the reception of the fossil shells long known as Lapides lenticulares and Nummulites.

Rotalites. A depressed orbicular, discoidal chambered shell, smooth on the upper, radiated on the under side, with tubercu lar and unequal points in the centre; the edge carinated, and having a small trigonal marginal opening. The fossil shell on which this genus was formed is figured and described by Guettard in his Memoirs on Fossils.

Turrilites. A spiral turbinated shell, with contiguous and visible turns, the sides articulated by winding sutures; transverse pierced septa, with foliated terminations, the opening round. The shells belonging to this genus are all fossil, and even the fragments of their casts are very rare. The characters of the shells of this genus are very striking, their internal structure being similar to that of the Ammonites, while they possess a turriculated or wreathed form.

Baculites. A straight cylindrical and rather conical shell; the sides articulated by winding sutures; the transverse septa terminating in foliaceous forms This genus is founded on a fossil shell, described by Faujas St. Fond in his Natural History of St. Peter's Mountain, near Maestrecht, and which he considers as a straight Ammonite.

Spirula. A shell partially or completely in a discoidal spire; the turns separate, and the last extending into a straight line; transverse smooth septa, pierced by a tube; the opening round. This genus comprises also the Lituites, a fossil shell, bearing a very close resemblance, in form, to the recent shells of this genus, but very far exceeding them in size.

Belemnites, a many chambered, straight, long, conical pointed shell, full at its summit, and possessing a lateral cleft.These are only known in a mineral state.

SHELL, in chemistry. Shells of marine animals, and of all eggs, consist chiefly of carbonate of lime, and yield a very pure lime, for which they are used on the seacoast. They afford, likewise, a small portion of phosphate of lime. There are two great classes of marine shells, the testaceous and crustaceous, the former are by much the most numerous, and include all the marine shell animals that have not legs, and the power of transporting themselves from place to place. The crustaceous shells are those of the lobster, crab, prawn, &c. who carry their shell as a protection from external injury, and not as a place of residence. Hatchet has made many experiments on shells, and he observes that marine shells, for the most part, are either of a porcella

Mr.

neous aspect, with an enamelled surface and fibrous texture, or they are composed of the substance called nacre, or mother of pearl. The first kind dissolved in acids with strong effervescence, and their solutions afforded no trace of the phosphate of lime: they contained only carbonate of lime, and the animal matter, which acts as a cement to this, and which he supposes to be albumen in various states of induration; this is in small proportion; hence shells exposed to heat exhale but little empyreumatic animal odour; they emit no smoke, and when dissolved in acids no vestige of it could be discovered. In shells of the other description approaching to nacre, the earthy matter is carbonate of lime, but in a smaller proportion, while the animal matter is in considerable quantity. These give out smoke and an empyreumatic odour, when exposed to heat; and when acted upon by acids, give out less carbonic acid gas, and leave a large quantity of a membranaceous or cartilaginous residuum. This substance often constitutes a large part of the shell, as in that of the oyster or muscle, and is so much indurated as to be no longer gelatinous; and in all shells of this division it appears to be deposited in layers, each having a corresponding coat of carbonate of lime.

SHELLS, in gunnery, are hollow iron balls to throw out of mortars or howitzers, with a fuze-hole of about an inch diameter, to load them with powder, and to receive the fuze: the bottom, or part opposite the fuze, is made heavier than the rest, that the fuze may fall uppermost ; but in small elevations this is not always the case, nor is it necessary; for let it fall as it will, the fuze sets fire to the powder within, which bursts the shell, and causes great devastation. The shells had much better be made of an equal thickness, for then they burst into more pieces.

SHELLS, message, are nothing more than howitz shells, in the inside of which a letter, or other papers are put. The fuzehole is stopped up with wood or cork, and the shells are fired out of a royal or howitz, either into a garrison or camp. It is supposed that the person to whom the letter is sent, knows the time, and ac. cordingly appoints a guard to look out for its arrival.

"To find the weight of a shell." Rule. Double the difference of diameters of the shell and hollow sphere, and seven times the result gives the weight in pounds, cutting off the two right hand figures of whole numbers. Ex. Let the diameter