FAMILIA I. Testacea Univalvia.
Sect. I. Testacea univalvia, testa pervia. Gen. 1. Echinus. Testa crustacea, ano verticali, tentaculis simplicibus. Gen. 2. Spathagus. Testa crustacea, ano infero, tentaculis penicillatis. Gen. 3. Dentalium. Testa calcarea, testa rudi, tentaculis nullis.
Sect. II. Testacea univalvia, testa patula. Gen. 4. Akeria. Apertura effusa, tentaculis nullis. Gen. 5. Argonauta. Apertura profunda, tentaculis binis. Gen. 6. Bulla. Apertura repanda, tentaculis binis fetaceis, colliculo extrinseco oculatis. Gen. 7. Buccinum. Apertura ovata, tentacul biinis triangularibus, angulo intrinseco oculatis. Gen. 8. Carychium. Apertura ovata, tentaculis biinis truncatis conspicuis, angulo extrinseco oculatis. Gen. 9. Vertigo. Apertura subquadrata, tentaculis biinis sublinearibus, apice oculatis. Gen. 10. Turbo. Apertura orbiculari, tentaculis biinis fetaceis, conspicuis, angulo extrinseco oculatis. Gen. 11. Helix. Apertura lunari, tentaculis quatuor linearibus, apice oculatis. Gen. 12. Planorbis. Apertura semilunari, tentaculis biinis fetaceis, angulo intrinseco oculatis. Gen. 13. Ancyur. Apertura totali tentaculis biinis truncatis, occultis, angulo extrinseco oculatis. Gen. 14. Patella. Apertura totali, tentaculis biinis fetaceis, occulto angulo, extrinseco oculatis.
To this account of the different methods of arranging shells we shall only add the system proposed by Da Costa in his Elements of Conchology. In this system the author adopts the usual general division into Univalves, Bivalves, and Multivalves.
I. Univalves are distributed into 16 families which are divided into four orders.
Order I. Simple; consists of four families. 1. Patella. 2. Haliotis. 3. Vermiculi. 4. Dentalia. Order II. includes only one family. 5. Polytalamia. Order III. Revolved. Fam. 6. Turbinata involuta. Order IV. Turbinated II. Bivalves composed of 3 orders.
Order I. With unequal valves, and shut close. Fam. 1. Pecten. Fam. 2. Spondylus. Fam. 3. Ostreum. Fam. 4. Anomia. Ord. II. With equal valves, and shut close, is divided into three sections, Sect. 1. Multarticulate. Fam. 5. Pectinoides. Fam. 6. Pectunculi. Fam. 7. Arca. Sect. 2. Articulate. Fam. 8. Pectunculus. Fam. 9. Tellina. Fam. 10. Placenta. Sect. 3. Inarticulate. Fam. 11. Margaritifera. Fam. 12. Mulculus. Ord. III. With valves that never shut close. Fam. 13. Chama, Gapers.
III. Multivalves contains one order. Fam. 14. Pholas. Fam. 15. Anatierae. Fam. 16. Balani.
CHAP II. OF THE ANIMALS WHICH INHABIT SHELLS.
BEFORE we proceed to the classification of shells, we shall here give a short description of the animals which inhabit them. Of these, however, a minute and accurate anatomical description is not to be expected; for little more is known of the structure of these animals than what has been given by naturalists concerning their external characters.
Some of the animals, which inhabit shells, are also found in the mollusca flate; that is, without any testaceous covering. Such, for instance, is the limax, or snail.
The animals which have been found inhabiting shells, are the following; viz. Doris, Triton, Afcidia, Tethys, Limax, Spio, Amphitrite, Terebella, Nereis.
Doris.—The body is creeping, oblong, and flat beneath; the mouth is placed below, on the forepart; vent behind on the back, and surrounded by a fringe. Feelers two or four, situated on the upper part of the body in front, and retractile within their proper receptacles.
The animal which inhabits the chiton belongs to this genus.
Triton.—The body is oblong, and the mouth is furnished with an involute spiral proboscis; tentacula or arms 12, fix on each side, divided nearly to the base. The hind ones cheliferous.
The triton inhabits different species of lepas.
Afcidia.—The body is fixed, roundish, and apparently issuing from a sheath; apertures two, generally placed near the upper end, one beneath the other. The animals are found in the sea, and adhere by their base to rocks, shells, and other submarine substances: they are more or less gelatinous. The only powers of motion which they possess seem to be that of contracting and dilating themselves alternately; by which means they are enabled to throw out the water which they take in with considerable force.
This animal inhabits the pholas, folen, some species of the mya, macra, and other bivalves.
Tethys.—The body is detached, rather oblong, fleshy, without peduncles: the mouth is furnished with a terminal cylindrical proboscis, under an expanded membrane or lip: apertures two, on the left side of the neck.
The tethys inhabits a great proportion of bivalve shells, as many species of tellina, cardium, macra, venus, ophrea, and others.
Limax.—The body is oblong, creeping, with a fleshy kind of shield above, and a longitudinal flat disc beneath: aperture placed on the right side within the shield: feelers 4, situated above the mouth, with an eye at the tip of each of the larger ones.
The animals belonging to this genus inhabit the turbinated univalve shells; but it appears that all the animals which inhabit these shells do not exactly correspond with the above generic characters.
Spio.—The body projecting from a tube, jointed and furnished with dorsal fibres; peduncles or feet rough with bristles, and placed towards the back; feelers 2; long, simple; eyes 2; long.
This animal inhabits some species of fabella.
Amphitrite.—Body projecting from a tube, and annulate; peduncles or feet small, numerous, with lateral fasciculi, and branchiae; feelers 2, approximate, feathered; no eyes.
The amphitrite inhabits some species of fabella and serpula.
Terebella.—Body oblong, creeping, naked, furnished with lateral fasciculi, or tufts, and branchiae; mouth placed before, furnished with lips, without teeth, and protruding a clavated proboscis; feelers numerous, ciliated, capillary, and placed round the mouth.
This animal is an inhabitant of many species of dentalium, serpula and fabella.
Nereis.—Body long, creeping, with numerous lateral peduncles or feet on each side; feelers simple, rarely none; eyes 2 or 4, rarely none. According to some naturalists, the nereis inhabits some species of fabella.
Sepia.—Body fleshy, receiving the breath in a sheath, with a tubular aperture at its base; arms 8, beset with numerous warts or suckers, and in most species 2 pedunculated tentacula; head short; eyes large; mouth resembling a parrot's beak.
The animal which inhabits the argonauta is considered by naturalists as belonging to this genus.
Clio.—Body oblong, nataur, generally fleathed and furnished with two dilated membranaceous arms or wing-like processes; tentacula 3, besides 2 in the mouth.
According to some naturalists, it is an animal belonging to this genus, which inhabits the argonauta. CHAP III. OF THE TERMS WHICH ARE EMPLOYED IN DESCRIBING SHELLS.
As it will tend to facilitate our progress in the study of Conchology, clearly to understand the terms which are employed in describing shells, and the names by which the different parts have been distinguished by naturalists; we shall here give a few definitions of the principal terms. And that these definitions may be easily consulted, we shall observe the same order as in the classification which is to be adopted. They may be conveniently arranged, therefore, into the three divisions of multivalves, bivalves, and univalves.
1. Explanation of the Terms of Multivalve Shells.
Multivalve shells are composed of more than two pieces.
Articulated (testæ articulatae), when the different pieces of which the shell is composed are so strongly united that they seem to form one shell.
Equivalve shells (testæ equivalves), when the valves of the two sides have the same form, size, and position.
A shell is said to adhere (testa adherens), when it is attached to solid bodies by some of the pieces of which it is composed: It is said to be loose (testa libera), when it is not attached by any point.
Pedunculated (testa pedunculata), when all the pieces of which it is composed, are supported by a tendinous peduncle which is fixed to solid bodies.
Tubular (testa tubulosa), when the greatest part of the shell is formed of a cylindrical tube.
Base of the shell (basis testæ), that part on which it is supported.
Ligament (ligamentum), is a membranous or tendinous substance which connects the valves together, and sometimes lines the cavity of the shells. Of this there are several varieties.
— scaly (ligamentum squamatum), when the surface is covered with small granular scales.
— prickly (ligamentum aculeatum), when the surface is furnished with small rough points.
— smooth (ligamentum lave), when the surface has neither points, scales, nor tubercles.
— punctated (ligamentum punctatum), when the surface is marked with small cavities.
Lid (operculum), is the name given to four small triangular valves articulated in the form of a cross, which shut up the superior orifice of some species of multivalve shells.
Peduncle (pedunculus) is the tendinous substance which supports some of the multivalve shells. It is flexible while the animal is alive, and is smooth or scaly.
Rays (radii); these are impressions on the external surface of some shells; they are of a conical form, having the vertex turned towards the base of the shell. They are only distinctly seen in adult shells.
— filiform (radii filiformes) are long and narrow.
— smooth (radii leves).
— striated (radii transversim striati.)
Valves (valvulae) are the different pieces of which multivalve shells are composed.
2. Explanation of the Terms applied to Bivalve Shells.
A bivalve shell is said to adhere (testa adherens), Bivalves, when it is fixed by any part of one of its valves to a solid body.
It is said to have ears (testa aurita), when it forms at its base, one or two compressed angles.
Gaping (testa hians), when the valves do not shut close.
Bearded (testa barbata), covered externally with an epidermis composed of strong hair or bristles.
Compressed (testa compressa), when the valves are flat, forming a small cavity.
Heart-shaped (testa cordata), having the form of a heart; (subcordata) approaching to that form.
Toothless (dentula), without teeth at the hinge.
Equilateral (testa æquilatera) when the anterior and posterior part of the shell is equal in form and figure.
Equivalve (equivalvis), when the two valves are similar in form and convexity.
Irregular (testa irregularis), when the form varies in the individuals of the species.
Lenticular (lenticularis), when the valves are round, and little elevated in the middle, and diminish gradually in thickness towards the edges.
Linear (testa linearis), when the length considerably exceeds the breadth, but without a cylindrical form.
Tongue-shaped (linguæformis), flat and oblong, having the two extremities round and obtuse.
Boat-shaped (navicularis) resembling the figure of a boat.
Pectinated (pectinata), when the valves being furnished with longitudinal ribs, have on their anterior surface ribs nearly transverse which form by their union with the first acute angles.
Radiated (radiata), when it is marked on the external surface with rays, ribs, or elevated striae, which proceed from the extremity of the summits, and terminate in the circumference of the valves.
Beaked (rostrata), when one of its surfaces, either anterior or posterior, being contracted and elongated, terminates in form of a beak.
Base (basis). The situation in which Linnaeus has described and considered bivalve shells, consists in placing the beaks of the shell turned downwards, in such a way that the ligament of the valves may be seen, so that the base of the shell is the region of its beaks.
Margin of the shell (margo testæ) signifies the whole circumference of the shell, parallel to the edge of the valves. It is divided into anterior, posterior, and superior.
— anterior (margo anterior), when the shell is placed on the beak of the valves, commences at the side of the ligament, on the fore-part of the mits, and extends to one third of the whole circumference of the valves,
Margin posterior (margo posterior), extends to one third of the circumference from the backs of the valves behind.
Superior (margo superior), includes the upper part of the circumference of the valves comprehended between the superior extremity of the anterior margin, and the superior extremity of the posterior margin. Hence the whole circumference of the shell is divided into 3 equal parts.
Margins of the valves (margines valvularum), signify the whole interior circumference of the valves, including about the breadth of a line of the outer edge. They are divided into
- furrowed (margines canaliculati), having on some part of the anterior circumference, a small gutter parallel to it. - notched (margines crenulati), furnished internally with rounded notches. - toothed (margines dentati), provided with pointed teeth. - folded (margines plicati), furnished with folds which reciprocally correspond with those of the opposite valve. - simple (margines simplices) having neither folds, teeth, nor notches. - striated (margines striati), having longitudinal striae.
Hinge. The hinge of a shell is the most solid and thickest part of the circumference of the valves, constituting their base. It is almost always furnished with teeth of different proportions, which serve to fix the valves together. The hinge is
- compressed (cardo depressus), formed of one compressed tooth. - lateral (cardo lateralis), when it is placed at one of the sides of the shell. - oblong (cardo oblongus), when it occupies the whole base of the shell. - reflected (cardo reflexus), when its edges are folded back externally towards the convexity of the valves. - terminal (cardo terminalis), situated at the inferior extremity of the shell. - truncated (cardo truncatus), when the base of the shell terminates transversely and suddenly, and the teeth of the hinge are fixed in this part.
Teeth (dentes), are solid protuberances, commonly pointed, with which the hinge of shells is usually furnished, and which are destined to fix the two valves together. They are divided into
- alternate (dentes alternati) when they are placed in a line parallel to the edges of the hinge; and when the teeth of one valve are received into the interstices of the teeth of the other valve. - articulated (dens infertus), when it is received in a corresponding cavity at the opposite valve. - forked (dens duplicatus seu bifidus,) having the point divided into two. - cardinal (dens primarius seu cardinalis), is the tooth which is placed immediately opposite. - compressed (dens depressus), which is very much flattened.
Teeth erect (dens erectus), when the valve is laid on the convex side, the tooth rises perpendicularly.
Longitudinal (dens longitudinalis), when it extends like a rib on the base of the valves.
The dish (discus), signifies the convex centre of the valves, which is usually situated between the belly of the shell and its limb.
Limb (limbus) is the circumference of the valves from the dish to their edges.
Belly of the shell (teftae umbo), is the most inflated part of the valves.
It is vaulted (umbo forniciatus) when in the interior of the valves it exhibits a cavity separated from the hinge by a vertical membrane.
Nates signify two protuberances of a conical figure, somewhat spiral, which accompany the external bale of most bivalve shells. They are
- flattened (nates depressae), when the surface is sensibly compressed. - approximate (nates approximate) meeting together, when the shell is shut. - horned (nates corniformes), when the angles being considerable, and their direction waved or spiral, they resemble a horn. - bent (nates incurvate), when the curvature of the one is directed towards that of the other. - separated (nates distantes), when they are separated from each other, at least the distance of a line. - distant (nates remotissimae), when the interval is very great. - reflected (nates recurvae), when the curvature is directed towards the posterior surface of the shell. - wrinkled (nates rugosae), when the surface is marked with unequal lines. - spiral (nates spirales), when the curvature exhibits more than one circumvolution.
Vulva, is situated at the lower part of the anterior margin of the valves. It is divided into
- hollowed (excilia, seu canaliculata), when it is marked with a groove during its whole length. - distinct (distincta), marked by a perceptible difference of colour. - lettered (scripta seu literata), when the surface is marked with lines resembling written characters. - inflected (inflexa), when the edge of the lips is bent towards the inner surface of the valves.
Anus, signifies an impression usually hollow, placed at the lower part of the posterior surface. It is divided into
- bordered (marginatus), when it is circumscribed by a distinct elevation. - heart-shaped (cordatus), exhibiting the form of a heart. - toothed (dentatus), furnished with teeth or notches. - lanceolate (lanceolatus), when the length is greater than the breadth, and the extremities are pointed. - open (patulus seu hians), forming by the separation of its edges, a considerable opening, which penetrates into the interior of the shell. - oval (ovatus), of an elliptical figure.
Valves, Valves, of bivalve shells, are divided into right and left, equal and unequal, equilateral and inequilateral, superior and inferior.
— right valve (dextra), is distinguished from the left, by placing the shell on its base, having the cardinal ligament before, and the anus behind. In this position the right valve of the shell corresponds to the left of the observer, and the left valve (sinistra) to the right of the observer.
— equal (eques), when the right valve corresponds with the left in form, size, and other external characters.
— superior (valvula superior). In an irregular shell, such as the oyster, one of the valves is attached to solid bodies; the other in this case is superior. This valve is sometimes called by Linnæus, the lid (operculum): in some species it is flat and small, and in others more convex than the inferior valve.
— keel-shaped (valvula carinata), when one part of their convexity presents a sharp edge.
— chambered (concamerata), when they exhibit in their cavity teflaccous plates, detached and raised.
— spinous (spinosae), when the whole surface is furnished with spines.
— banded (fasciatae), exhibiting large coloured transverse stripes or bands.
— lamellated (lamellofae), when the surface is furnished with plates more or less separated.
— radiated (radiatae), exhibiting divergent or coloured rays.
— sinuated (lacunofae), when one of the valves has a sensible depression at the middle of its margin, and a corresponding elevation of the opposite valve.
— striated (striatae) when the surface is marked with striae.
— transverse, when the striae are parallel to the margin of the valves.
— longitudinal, when they run from the base to the circumference.
Muscular impressions (impressiones), are marks on the interior surface of the valves, where the muscles of the animal are attached.
— solitary (foliaris), when the inner surface of each valve has only one.
— double (duplicatae), two on the inner surface of each valve.
— triple or ternate (ternatae), three in each valve.
Ligament (ligamentum), is a horny substance, of little flexibility, which unites the two valves near their base, and which in almost all bivalve shells is placed at the lower part of their anterior surface. It is divided into:
— gaping (hians), when its upper extremity is divided into two.
— double (duplex), when under the external ligament there appears a second, in a particular hollow of the hinge, which does not appear externally.
— internal (internalis), when it unites the valves without appearing externally.
— profound (retractum seu intractum) when it is so deep in the future as scarcely to be seen when the valves are shut.
truncated (truncatum) when shorter than its future.
Furrows (falsi), are those impressions or interfices between the ribs or rays on the surface of the valves.
— square (quadrati), when the bottom is flat.
— lamellated (lamellata), when the bottom is marked with small transverse scales.
— punctated (excavato punctati), when the whole surface is marked with small cavities or dots.
3. Explanation of Terms applied to Univalve Shells.
The base, (basis) is the most elevated part of the Univalves shell, opposite to the spire. It is divided into:
— notched (emarginata), when it is accompanied with a deep notch.
— tubular (tubulosa seu cordata), when it is formed by a tube.
— simple or entire (simplex aut integra), without notch or tube.
Summit (vertex) signifies the top of some patellæ, and from its position is central, marginal, or submarginal.
The shell (testa) is divided with regard to its position into superior and inferior.
The anterior part (pars antica), is that which forms the spire of the shell; and it is also the superior part.
The form of shells is:
— bordered (marginata), when the two sides of the opening are broader and thicker than the rest of the diameter.
— chambered (polythalamia), when it is internally divided by different partitions parallel to the opening.
— convoluted (convoluta), when the spires turn round a lengthened cone, nearly vertical to each other.
— rooted (radicata), when it is attached to a solid body by a ligament proceeding from its base.
— interrupted (interrupta), when the successive additions to the shell are marked with distinct rings.
— umbilicated (umbilicata), when the axis round which the sphere turns, being empty, forms a cavity at the base of the shell, whose diameter is at least a sixth part of that of the shell.
— imperforated (imperforata seu exumbilicata), when its inferior axis has neither hole nor umbilicus.
— oval or elliptic (ovales), the longitudinal diameter exceeding the transverse, and the two extremities equal and a little contracted.
— egg-shaped (ovata), the longitudinal diameter exceeding the transverse, and the extremities terminated by the segment of a circle.
— beaked (rostrata), when the two extremities, sometimes tubular, form a projection in form of a beak.
— imbricated (imbricata), when the surface is covered with parallel scales, so arranged as to cover each other.
— turbinated (turbinata), when the belly of the shell is large in proportion to the spires, which seem to proceed from its center. Opening or mouth (apertura), is that part of the cavity of the shell which is visible. It is
- angular (angulata), when its circumference has several angles. - gaping (dehiscens), when one of the extremities is wider than the other. - bimarginated (bimarginata), when the right lip forms a double margin. - compressed (coarctata), when it is distinctly flattened. - semicircular (semiorbiculata), when it forms half a circle. - linear (linearis), when it is narrow, and the length considerably exceeds the breadth. - longitudinal (longitudinalis), when the length is greater than the breadth, and the greatest dimension is parallel to the axis of the shell. - orbicular (orbicularis), forming an entire circle. - striated (stria), when the cavity is marked with striae, parallel to the direction of the convolutions. - transverse (transversa), when the breadth is greater than the length.
Pillar (columella), is that part of the shell situated within the opening, near its axis, round which the spires turn. It is brought into view by dividing the shell its whole length. It is
- flattened (plana), when the surface is flat and smooth. - caudated (caudata), when it is lengthened beyond the base of the shell. - folded (plicata), marked with transverse and distinct folds. - spiral (spiralis), proceeding from the base, and forming a small, twisted elongation. - truncated (truncata), cut transversely at the base.
Convolutions (anfractus), are the turnings of the spire round the pillar, from the opening to the base of the shell. They are
- bifid (bifidi), when each is divided into two equal parts by a furrow or spiral line. - grooved (canaliculati), when the superior edge is marked with a groove. - keel-shaped (carinata), when the outer turn of the shell is marked with an angle more or less acute. - crowned (coronata), when the upper surface is bordered at a little distance from the sutures, with a single row of tubercles or spinous scales. - dextral (dextri), turning from the left to the right. - sinistral (sinistri), turning from the right to the left. - lettered (scripti), marked with characters. - spinous (spinosi), having short spines on the surface. - entire (simplices), without furrows or tubercles. - banded (fasciati), when the surface is marked with broad coloured stripes. - lamellated (lamellati), the surface marked with longitudinal or transverse excrescences, and laminated like membranes.
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Sutures (fissurae), signify the place of junction of the different convolutions, forming a spiral line. They are
- grooved (canaliculatæ), when they are so deep as to form a small canal. - notched (crenulatæ), when the points of contact are marked with notches. - double (duplicatæ), accompanied with two striae, which run parallel. - effaced (obsoletæ), when the place of junction is not perceptible.
Siphon (siphon), is a small canal situated in the internal part of the shell of the nautili, which penetrates into the divisions of which it is composed. It is
- central (centralis), when it is situated in the middle of the divisions. - lateral (lateralis), situated at one side. - oblique (obliquus), cutting the axis of the divisions obliquely.
Veins (varices) are elevations or ribs, running in the direction of the length of the shell, formed by the junction of the different additions which the shell has received. They cut the convolutions of the spire transversely. They are
- continued (continuatae), proceeding from the base of the spire to the convolution at the opening, without interruption. - spinous (spinosæ), furnished with strong spines. - interrupted (decussatae), not corresponding with the different convolutions. CHAP. IV. CLASSIFICATION OF SHELLS.
SHELLS are divided by Linnaeus into multivalve, bivalve, and univalve. In the following classification the same arrangement will be adopted; and we shall first exhibit in one view the characters of each genus, in the original language of Linnaeus, with a translation opposite, for the sake of the English reader; so that the genus of any shell may be easily determined. In describing the species, we shall observe the utmost brevity, giving such characters only as are necessary to afford precise marks of distinction. In arranging the species under each genus, the British species will be distinguished with an asterisk; so that, with the advantage of a general classification, this will answer the purpose of a British conchology.
GENERIC CHARACTERS.
I. MULTIVALVE SHELLS.
1. Chiton. Animal doris. Testae plures, secundum longitudinem fibi appositae dorso incumbentes.
2. Lepas. Animal triton. Testa basi affixa multivalvis: valvis inaequalibus erectis.
3. Pholas. Animal ascidia. Testa bivalvis divaricata, cum minoribus accefforis difformibus: cardo recurvatus cartilagine connexus.
II. BIVALVE SHELLS.
4. Mya. Animal ascidia. Testa bivalvis bianis, ut plurimum, altera extremitate: cardo dente (plerique uno) folido, crasso, patulo, vacuo; nec inferto testae appositae.
5. Solex. Animal ascidia. Testa bivalvis oblonga, utroque latere bianis. Cardo dens subulatus reflexus, (ape duplex, non infertus testae appositae, margo lateralis magis obfoletus.
6. Tellina. Animal tethys. Testa bivalvis, anterius hinc ad alterum latus flexa. Cardinis dentes ut plurimum tres: laterales plani alterius testae.
7. Cardium. Animal tethys. Testa bivalvis subaequilatera, aequivalvis plerumque convexa, longitudinaliter costata, striata aut fulcata, margine dentata. Cardo dentibus mediis binis alternatis: altero ut plurimum incurvo; lateralibus remotis infertis.
8. Macra. Animal tethys. Testa bivalvis, inequilatera, aequivalvis. Cardo dente medio complicato cum adjecta foveola, lateralibus remotis infertis.
9. Donax. Animal tethys. Testa bivalvis, margine saepe crenulato antico obtusifimo. Cardo dentibus duobus; marginalique solitario (rarius duplici, triplice, aut nullo) subremoto sub ano.
10. Venus. Animal tethys. Testa bivalvis; labris margine antico incumbentibus. Cardo dentibus tribus, omnibus approximatis, lateralibus apice divergentibus.
1. C. Animal inhabiting the shell a doris. Shell consisting of several segments or valves disposed down the back.
2. L. Animal a triton. Shell affixed at the base, and consisting of many unequal erect valves.
3. P. Animal an ascidia. Shell bivalve, divaricate, differently shaped; accessory valves: hinges bent back, united by a cartilage: beneath the hinge internally, is an incurved tooth.
4. M. Animal an ascidia. Shell bivalve, generally gaping at one end. Hinge with broad, thick, strong teeth (eldom more than one), and not inserted into the opposite valve.
5. S. Animal an ascidia. Shell bivalve, oblong, open at both ends. Hinge with a subulate, reflected tooth, often double, and not inserted in the opposite valve, the lateral margin more effaced.
6. T. Animal a tethys. Shell bivalve, generally sloping on one side, in the fore part of one valve a convex, of the other a concave fold. Hinge usually with three teeth; the lateral ones in one shell being smooth.
7. C. Animal a tethys. Shell bivalve, nearly equilateral, aequivalve, generally convex, longitudinally ribbed, striated or grooved, with a toothed margin. Hinge with two teeth near the beak, and a larger remote lateral one on each side, each locking into the opposite.
8. M. Animal a tethys. Shell bivalve, of unequal sides, and aequivalve. Middle tooth of the hinge complicated, with a small hollow on each side, lateral ones remote and inserted into each other.
9. D. Animal a tethys. Shell bivalve, generally with a notched margin: the frontal margin very obtuse. Hinge with two teeth, and a single marginal one placed behind (rarely double, triple, or none).
10. V. Animal a tethys. Shell bivalve; the frontal margin flattened with incumbent lips. Hinge with three teeth, all approximate; the lateral ones divergent at the tip. 11. Spondylus. Animal tethys. Testa inaequivalvis rigida. Cardo dentibus duobus recurvis, cum foveola intermedia.
12. Chama. Animal tethys. Testa bivalvis crassior, cardo callo gibbo, oblique inferto fossula obliqua.
13. Arca. Animal tethys? Testa bivalvis equivalvis. Cardo dentibus numerosis, acutis alternis infectis.
14. Ostrea. Animal tethys. Testa bivalvis (plurimis inaequivalvis subaurita). Cardo edentulus, foliula cava, ovata, sulcisique (in plurimis) lateralibus transversis.
15. Anomia. Animal corpus ligula emarginata ciliata: ciliae valvae superiori affixis: brachiis duobus linearibus corpore longioribus conniventibus recteortis, valvae alternis utrinque ciliatis: ciliae affixis valvae utrique: testa inaequivalvis, valva altera planulicula, altera basi magis gibba: parum altera basi fape perforata. Cardo cicatricula lineari, prominente introfusum dente laterali; valvae vero planioris in ipso margine. Radii duo offici pro basi animalis.
16. Mytilus. Animal ascidia? Testa bivalvis, rudis, sepium affixa bysio, ut plurimum, crassiori. Cardo in plurimis edentulus, distinctus, paucis exceptis, linea subulata, excavata longitudinali.
17. Pinna. Animal limax. Testa sub-bivalvis fragilis, erecta hians, emittens barbam bysifinam. Cardo edentulus, coalitis in unam valvis.
III. UNIVALVE SHELLS.
18. Argonauta. Animal sepia aut clio. Testa univalvis, spiralis, involuta, membranacea, unilocularis.
19. Nautilus. Animal? Testa univalvis, isthmis perforatis concameratis, polythalamia.
20. Conus. Animal limax. Testa univalvis convoluta, turbinata; apertura effusa, longitudinalis, linearis, edentula, bas integra; columella levis.
21. Cypraea. Animal limax. Testa univalvis, involuta, sub-ovata, obtusa, laevis. Apertura utrinque effusa, linearis utrinque dentata longitudinalis.
22. Bulla. Animal limax. Testa univalvis convoluta, inermis. Apertura sub-coarctata, oblonga, longitudinalis, bas integerrima. Columella obliqua, levis.
23. Voluta. Animal limax. Testa unilocularis spiralis. Apertura ecaudata, sub-effusa. Columella plicata: labio umbilicovo (ut plurimum) nullo.
24. Buccinum. Animal limax. Testa univalvis, spiralis, gibbosa. Apertura ovata definens in canaliculum (retusum lacunum) dextrum, cauda retusa. Labium interius explanatum.
25. Strombus. Animal limax. Testa univalvis, spiralis, latere ampliata. Apertura labro faepius dilatato, definens in canalem finitrum.
26. Murex. Animal limax. Testa univalvis, spiralis, exasperata suturis membranaceis. Apertura defi-
11. S. Animal a tethys. Shell hard, solid, with unequal valves. Hinge with two recurved teeth, separated by a small cavity.
12. C. Animal a tethys. Shell bivalve, rather coarse. Hinge with a callous protuberance, obliquely inflected in an oblique hollow.
13. A. Animal a tethys? Shell bivalve equivalve. Hinge with numerous sharp teeth, alternately inflected between each other.
14. O. Animal a tethys. Shell bivalve, generally with unequal valves, and slightly eared. Hinge without teeth, but furnished with an ovate cavity, and in most with lateral, transverse furrows.
15. A. Animal an emarginate, ciliated, strap-shaped body, with brittle attached to the upper valve; arms two, linear, longer than the body, projecting and approaching together, alternate on the valve, and ciliated on each side, with brittle affixed to each valve. Shell inequivalve, one of the valves flatish, the other protuberant at the base; one of the valves often perforated near the base. Hinge with a linear prominent cicatrix, and a lateral tooth placed within; but on the very margin of the flat valve there are two bony rays for the base of the animal.
16. M. Animal an ascidia? Shell bivalve, rough, generally affixed by a byssus or beard of silky filaments. Hinge mostly without teeth, and in most cases with a subulate, hollow, longitudinal line.
17. P. Animal a limax. Shell bivalve, brittle, gaping at one end, and having a byssus or beard. Hinge without teeth, the valves being united into one.
18. A. Animal a sepia or clio. Shell univalve, spiral, involute, membranaceous, one cell.
19. N. Animal? Shell univalve, divided into several chambers communicating with each other.
20. C. Animal a limax. Shell univalve, convolute, turbinate; aperture effusa, longitudinal, linear, without teeth; entire at the base. Pillar smooth.
21. C. Animal a flag. Shell univalve, involute, subovate, smooth, obtuse. Aperture effusa at each end, linear, extending the whole length of the shell, and toothed on each side.
22. B. Animal a limax. Shell univalve, convolute, without teeth. Aperture a little narrowed, oblong, longitudinal, quite entire at the base. Pillar oblique and smooth.
23. V. Animal a limax. Shell one cell, spiral. Aperture without a beak, and somewhat effusa. Pillar twisted or plaited: generally without lips or perforation.
24. B. Animal a limax. Shell univalve, spiral, gibbous. Aperture ovate, ending in a short canal, leaning to the right, with a retuse beak. Internal or pillar lip expanded.
25. S. Animal a limax. Shell univalve, spiral, enlarged at the side. Aperture dilated with the lip expanding, and ending in a groove towards the left.
26. M. Animal a limax. Shell univalve, spiral, rough, with membranaceous sutures. Aperture oval,