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be slit, canaliculated, consolidated, crenu. To determine the side to which a valve Jated, or dentated: it may also have a su- belongs, the shell need only be placed on peradded cullus. The opening varies the hinge, with the anterior side forward, much in different shells ; and where it when it directly shows itself. narrows it acquires the name of throat; it In some irregular shells, as of oysters, terminales in a canal. The lip is eared, and spondyles, the shells are divided into digitated, alated, grooved, slit, or wrin. upper and under, the upper shell being kled; the form of the opening depending flatter than the under. In the Terebramuch on that of the lip; it bence becom- tuæ, the upper shell, the beak of which ing angular, round, semicircular, longitu. is pierced, is more tumid than the under: dinal, transverse, linear, gaping, com. but in most shells, as in the Pectens, and pressed, or reversed. The openings of the oysters, the upper valve is almost al. shells are sometimes closed by a shelly or ways the least tumid. cartilaginous plano-convex body, termed The hinge is, in general, furnished operculum, which is disposed between with teeth ; but sometimes it is without. the two lips, and fitted to the form of the When placed on the side, they are opening.. The flat suurface of this body is said to be lateral; and when on the marked by a spiral line.
inferior extremity, terminal. The cenA bivalve shell has the two valves tral teeth, essential to the genus, are which constitute it connected at the ba- termed the cardinal teeth ; and the sis, or inferior margin: opposite to which others, accessory or secondary. The is the superior margin: the shell being teeth are in some shells articulated, in supposed to be placed on the hinge, its a cavity, in the opposite valve ; in margin is divided into the anterior and others, they are not. In multivalves the posterior margin. The length of the also the shell is the combination of all shell is measured from the inferior to the the valves, whether connected by articu. superior margin, and the breadth from lation, or by ligaments. the anterior to the posterior margin. The From the observations and experiments belly is the most tumid part, and the of Reaumur, which have been since conbeaks, the prominences over the hinge, siderably extended by Bruguiere and are of a conoidal and spiral form. At the others, the formation and growth of shells basis of the shell is the hinge, by which have obtained considerable illustration. the valves are moved on each other; and Leuwenhoeck, Swammerdam, Lister, and in the anterior chink a ligament is placed, others, had observed, that, at the first by which the valves are closely connect. escape of the animal from the egg, it was ed. This chink is formed by a slight se. invested by a complete spiral turn, at least paration of the valves at this, the anteri. of the shell: and it appears, from the obor part, which having a distinct surface servations of Adanson, that viviparous from the general disk, and being indeed shell-fish are likewise brought forth in a separated from it by an angle, or by a rais similar state. The growth of shells was ed or sunk line, it may be distinguished discovered by Reaumur to take place in as the corslet ; this surface is particularly that which is most distant from ibe first distinguished in the shells of the Venus formed part. Here a part of the animal kind. On these parts, in some species, exists, which is not yet covered with shell, are spines, in others various markings, but which is beset with a vast number of and in others these parts are plin. At vessels, which separate, and deposit on the lower part of the anterior margin of the existing edge of the shell those gluthe valves, within the limits of the cors. tinous and calcareous matters, by which let, and above the ligament, is a part ge- its due increased extent of surface is ob. nerally distinguishable from the rest of tained. In proof of this being the process the surface by a difference in the colour, by which the augmentation of the shell is striæ, &c. 'This part varies in its form, effected, he broke the shells of various being canaliculated, replicated, &c. Its living testaceous animalsin different parts, edges are termed lips.
and was thus enabled to perceive, that On the other side of the hinge, on the the newly added matter was not deposit. posterior part, and near the hinge, is ge- ed line after line from the shell, at the nerally a lunated depression; the cres- edges of the fractured part; but was secent, like the part just described, va parated, in a pellicle, from the body of ries in its form and markings in different ihe animal, and thus applied at once to shells. Both these parts derive half their the whole of the vacuity. Those, who de form from each of the valves; and are nied this mode of increase, denied also the consequently separated in the middle. removal of the posterior termination of the worm, from the extreme termination unnecessarily multiplied the number or of the first formed spire. But it is cer- species of these shells. tain, that the animals in many shells have The highly ornamented surface of these their posterior termination attached to shells is formed at two different periods, the point of the shell only in their earliest and by two different processes. The first stages; and that, when older, it is found appears to be that deposition which takes adherent to the second or third turn : and place from the surface of the body of the it has also been ascertained that the tail animal; and in which but little takes of the Nerite is attached beneath the left place different from what occurs in shells or columellar lip. In proot of these ani. in general. But as the age of the animal mals possessing this power of removing advances, this surface is covered by an. themselves from these turns of the shell, other ; the primitive colours disappear, or indeed from those parts in which their others are disposed over them, and the residence is no longer necessary, the cir- substance itself of the shell becomes concumstance may be adduced of the animal siderably thickened. This process is per. belonging to the Porcellanea, sometimes formed by a simple, but most curious or. abandoning its old shell, and forming a ganization. Two soft, membraneous new one.
Haps, or winged processes, pass out of The various tints of different colours the opening of the shell, turn back on the with which shells are so beautifully external convex surface, and cover it so adorned, result, according to the remarks completely as not to leave the least porof the same ingenious naturalist, from an tion to be seen at the line where they economy and organization somewhat si. meet each other, on the back of the shell. milar to that which has been juist men. From the superior surface of these mem. tioned. On the neck of the animal, that braneous bodies, that surface which clings part from which the matter of the shell to the convex part of the shell exudes is supposed to be secreted, the colours of that secretion, by which the shell is inthe shell may be detected. Thus, it the creased in bulk; and a new arrangement ground of the shell be yellow, and it be of the beautiful colours of its drapery is marked with dark brown or black bands, effected. then the neck of the animal will be seen Bruguiere ascertained this formation of of a white, inclining to a yellow hue, with a second surface by actual observation at dark spots, answering in their number Madagascar ; and the fact derives addiand direction to the bands observable in tional proof from the pale line which the shell itself: the colouring matter ap- passes frequently along the back of these pearing to be here disposed, ready for its shells, marking the part where the edges deposition, with the other substances of of the membraneous wings met. Still the shell. In this manner, and on these more positive prooi is rendered by rub. principles, bas Reaumur been able to ex. bing down the second coat, when the plain almost every circumstance, respect. markings of the first coat will make their ing the varieties of form and of colour appearance, which are observable in these bodies. Although the colours are thus dispos.
But a circumstance is observable in the ed by the animal, the action of light apOlives and the Porcellaneæ, to which pears to have a considerable effect in aug. Reaumur has not attempted to apply his menting their brilliancy: climate also ocdoctrine. In these shells the colours are casions considerable differences in this disposed in two layers, the outer of which respect; hence the shells obtained from is the production of an organization dif. the torrid zones are much more rich in ferent from that of any of the other inha. their colouring than those which are bitants of shells, and from which pro. found in the more temperate zones. But ceeds an operation, also different from notwithstanding the circumstance just nowhat occurs in any other instance. At ticed, there is great reason for attributing the period at which Reaumur wrote, se- the high degree of colouring in shells veral of the olives and of the cowries, in more to the effects of light than to the consequence of certain differences of co- heat of the climate. lour, and of some difference also in their It is not the colouring only of the seforms, were considered as of different cond coat of the porcellaneous shells species from others, of which they were which is given by this second operation; in fact individuals of the same species, the several asperities observable in vari. but had not yet acquired their perfectous shells, as in the Cypræa tuberculosa, state. For want of reckoning upon this and in the Cypræa pediculus, are supercircumstance, the celebrated Linnæus has added at the same period.
The form of the shell will necessarily jecting from the general surface; and depend on that with which the worm is by a repetition of this process, a succesfirst invested ; but it is a curious subject sion of ihese ribs, with intermediate spaof investigation, on what peculiar modifi. ces of the common surface, such as frecation of the animal depends the spiral quently exists in turbinated shells, would form of univalve shells. This has been consequently be formed. attempted to be explained by Reaumur, From a process exceedingly similar, we by a very simple peculiarity of organiza. may suppose the formation of the warted tion ; it being sufficient, he supposes, to protuberances and tubercles to have pro. consider the fibres on one surface of the ceeded; corresponding fleshy projecbody to be shorter than those on the op. tions, existing on that part of the surface posite surface. From this inherent pecu- of the animal to which this part of the liarity of formation, the prolongation of shell has been applied, having been the the animal must necessarily be in a spiral moulds, as it were, on which these have form; and from the various obliquities of been formed. Whilst these fleshy protudisposition of these shorter and longer berances have continued, these processes fibres will proceed that variety of direc. have remained hollow ; but where the tion, in which the spiral turns will be dis- fleshy protuberances have been diminishposed.
ed, these processes have become partly The umbilicus, the cavity in the centre filled up; and where they have been reof the spire, which is seen in the lower moved, these have become entirely solid, part of the shell, depends on the direction from the deposition of additional shelly in which the animal has extended the matter from the surface of the animal, the shell. Thus, if the turns of the spire existence of the cavities being necessary have been carried round an axis of a co. no longer than the continuance of the nical form, each turn having departed fleshy processes themselves. more and more from the centre of the The production of the spinous proshell, an umbilicus will be formed, more cesses, so frequent on many shells, apor less open, as the terms depart more or proaches still nearer to that of the ribbed less from the centre. But if the terms are protuberances, since they have been formina le round an axis so straight and fine ased by little, long, tongue-like processes, to occasion the turns to touch each other, with which the neck of the animal is be. then no umbilical cavity will be formed at set, and which have served in the same the bottom of the shell.
manner to produce these spines, as the To enable us to account for the longi. neck of the animal bas served to form the tudinal, raised and thickened ribs, which borclered edge of the shell, by an addicross, in a longitudinal direction, the tion of the testaceous matter at each time turns of the spire, and which are termed the neck of the animal, at certain periods, varices by Linn:us, it is necessary to re- passed out or returned into the shell. fer to the formation of the opening of land The confirmation of this being the mode sheils, when they have obtained their full of their formation is yielded, by the cirgrowth. At this period the tip of the cumstance of these spines being ranged shell, from the frequent egress and re- in lines, at equal distances, on the ribbed turn of the animal through the opening, protuberances, or varices of Linnæus, the has an additional portion of the testaceous formation of which has not only been sie matter repeatedly deposited upon it, by milar, but simultaneous which it acquires a bordered edge, which T he production of the channel, or differs in size and thickness in the shells gutter, (the cauda of Linnæus,) depends of different animals. But in sea-shells, on circumstances extremely similar to the growth of the shell is not completed those on which has depended the formaon the formation of this bordered lip; tion of the various parts already noticed. the continuation of the spire still proceed. All those animals whose shells have this ing atier its formation. To explain the termination, are endued with an organ of formation of these ribbed longitudinal pro- a cylindrical form, capable of being conjections, it is therefore only necessary to tracted and extended, so as to allow the suppose the animal, after having formed animal to explore its path, or to attach the bordered edge to the mouth of the itself to neighbouring bodies. By the shell, to have proceeded uninterruptedly frequent employment of this organ, and for a certain period in the formation of the by its necessarily accompanying frequent common smooth surface of the shell, which alternate contractions and extensions, its as it would then extend beyond the lately surface, which possesses the property of formed lip, would now renderit a rib pro. exuding a testaceous substance, must at
each passage and return contribute to the
DIVALVES, OR CONCIL. formation of this canal, which would serve the purpose of a sheath to it.
4. Mya. Gaper. Shell generally gap. By an ingenious application of these
ing at one end; the hinge with, for the
most part, a thick, solid, spreading tooth, principles of Reaumur, Bruguiere and Brogniart (* Bulletin de la Societé Philo
not inserted in the opposite valve.
5. Solen. Razor-shell. Shell oblong, mathique," No. 25.) have very satisfacto
gaping at both ends ; hinge with a suburily explained the production of the seve
lated reflexed tooth, often double, not inral fissures, striæ, grooves, and other mo. difications of the forms and surfaces of dif.
serted in the opposite valve : the lateral
margin rather obsolete. ferent shells. The author last mentioned has shown, tbat, in some instances, the or.
6. Tellina. The foreside of the shell gan by which soine changes have been
sloping downwards; the hinge, in geneproduced in the later formed part of the
al, with three teeth; the side teetli, in shell was not acquired by the animal until
one of the valves, being either flat or it had obtained its full size.
By an appli. cation of these principles to bivalves, and
7. Cardium. .Shell with equal and even to multivalves, their peculiarities of
nearly equilateral valves, longitudinally form have also been very ingeniously ac
ribbed, or sulcated, the margin dentai. counted for. It has been found, that, in
ed; the hinge having, in the middle, two bivalves, the part of the animal which is
alternating teeth, one commonly incurvtermed the mantle is the organ on which
ed, and two lateral, remote teeth, insert.
ed into each other. the peculiarity of the form of each chiefly depends; it answering in this respect to
8. Mactra. Shell with equal, but inethe collar, or neck of the animal, belong
quilateral valves; the hinge a complicat.
edi, central tooth, with an adjoining pit, ing to univalve shells.
and remote lateral teeth, inserted in the It does not seem necessary here to dwell opposite valves. on the labours of those, who, previous to 9. Donax. The anterior margin of the the time of Linnæus, had endeavoured to shell very obtuse, the margin often credispose of shells under the most compre. nulated, two teeth at the hinge, and on frensive and distinctive arrangement. the binder margin a single one, (rarely Whatever had been done before with this two, or three, or none,) somewhat review gave way to the more lucid and cor. mote. rect disposition which Linnæus adopted; 10. Venus. The lips lying over the but this is certainly by no means the ne anterior margin; the linge with three plus ultra : other divisions appear in some teeth close together, the lateral ones di. instances deserving of adoption, and new verging from the apex. genera require to be admitted. It is, 11. Spondylus. With rigid, unequal therefore, intended to give here Lin. valves; the hinge being formed by two næus's arrangement of the genera, omit. recurved teeth, with a cavity between. ting the species; afterwards to give that 12. Chama. The shell heavy; the hinge which has been adopted by Du Bosc, a gibbous projection, inserted in an ob. . agreeable to the discoveries and obser. lique cavity; the fore parts closed, with. vations of Lamarck, Brugulere, and out cartilages. others; and to offer a few explanatory 1 3. Arca. Equivalved; the hinge with remarks, for the purpose of showing numerous, acute, and alternately inserted the propriety or impropriety of the de. teeth. ' viations from the arrangement of Lin. 14. Ostrea. With unequal valves, 1æus.
sometimes eared; the hinge an ovate ca
vity, without teeth, but, in general, with MULTIVALVE SHELLS.
lateral transverse striæ ; no space or de.
pression at the ligament. Genus 1. Chiton. The animal covered 15 Anomia. The valves unequal, one by several shells lying on each other along Alattish, the other gibbous, and one of the back.
them often perforated at the base; the 2. Lepas. The shell, which is formed hinge a linear projection, with a lateral of several unequal and erect valves, is af. tooth, which, in the flat valve, is inserted fixed by its base,
in the margin; two bony rays support the 3. Pholas. Shell bivalve and divaricats animal. ed, with smaller, accessory, differently 16. Mytilus. Shell coarse, generally formed pieces at the binge.
affixed by its byssus; hinge generally
without teeth, being distinguished by a tened; the disk almost always perforated linear, subulated, longitudinal, furrow. with a row of holes.
17. Pinna. A sub-bivalve, brittle, 32. Patella. Nearly conical, and without erect, and gaping, haring a silky beard. a spire. The hinge without teeth; the valves ad. 33. Dentalium. Tubular, straight, with here on one side.
one chamber, open at both ends.
34. Serpular. Tubular, adhering to UNIVALVE SHELLS, OR COCHLEÆ. other bodies, often intercepted by entire
partitions. 18. Argonauta. Shell spiral, invo. 35. Teredo. Round, bending, and lodglute, membranaceous, and with one cham- ed wood. ber.
36. Sabella. Tubular, formed by grains 19. Nautilus. Divided into many cham- of sand, on a membranous sheath bers, by partitions, perforated with pro- The French naturalists, whose late exjecting pipes.
ertions have added much to the funds of 20. Conus. Convoluted and turbinat. this science, have thought it necessary to ed shell; the aperture longitudinal, li. adopt some changes with respect to the near, open at both ends, and without preceding arrangement. These changes teeth ; the base entire, and the columella would, indeed, derive some support from smooth.
the high characters which have suggest21. Cypræa. Involuted, sub-ovate, ob. ed them; no one having done more of tuse, and smooth ; the opening longi. late years to the advancement of this spetudinal, linear, dentated on each side, cies of knowledge than Bruguiere and Laand extended to both ends of the marck. Their observations shall there. shell.
fore be introduced under the several ge. 22. Bulla. Convoluted, without spire, nera to which they apply, whilst the oropening longitudinal, oblong, and con. der in which they are taken shall be that tracted at the ends, entire at the base; of Bosc, in “ Histoire Naturale des Cothe columella oblique and smooth.
quilles.” 23. Voluta. Unilocular and spiral; the aperture without a tail, and somewhat
MULTIVALVE SUELLS. open at both ends : columella plaited, with no inner or columellar lip, nor um Lamarck thinks that Pholades should bilicus.
be regarded as bivalves, having accessary 24. Buccinum. Spiral and gibbous ; pieces, and that the Oscabrius (Chitons) the aperture oval, terminating in a gut. should be considered as naked mollusca, ter, which, with the cauda, runs out to whose backs are beset with small testathe right; the interior lip smooth. ceous laminæ. Bosc, however, in confor.
25. Strombus. Spiral, with one side mity with accustomed practice, considers large, the aperture frequently with a di. them among the multivalve shells lated outer lip, terminating in a gutter Dacosta (Conchology, 8vo. p. 97 ) ohwbich turns to the left.
serves, that “The Greek name lepas, al26. Mures. Spiral and rough, with ways synonymous with the Latin name pa. membranaceous sutures; the aperture tella, the latter signifying little sacrifice ending in an entire, straight, or somewhat dishes, or saucers, was given to limpets ascending gutter.
from the earliest Grecian times, and the 27. Trochus. Spiral, and nearly coni. Roman name from their resemblance to cal; the aperture nearly tetragonal or those little dishes; yet Linnæus wantonly rounded, contracted transversely above; transposes the name of Lepas to the Ba. the columella oblique.
lani." The French naturalists have still 28. Turbo Spiral and solid ; the aper. continued the name of Lepas to the Pa. ture contracted, orbicular, and entire. tellæ ; and have separated those bodies
29. Helix. Spiral, subdiaphanous and which Linnæus had placed under the gefragile ; aperture close at the ends; with nus Lepas into two genera : 1. Anatifa, in lunated, or partly circular, as if a seg. a cuneiform shell, composed of several fat ment of the circle had been cut off unequal valves, connected together by a
30. Nerita. Spiral, gibbous, and Mat- membrane, and united to the extremity of tish below; the aperture semiorbicular, a tendinous tube fixed by its base; and, or semilunar; the lip of the columella 2. Balanus, a conical mullivalve shell, fixtransverse and flaitishly truncated. ed by its base, and composed of six arti
31. Haliotis. Ear-shaped ; the mouth culated valves, the openings closed by an gpread open; the spire lateral and flat- operculum, with four valves. These