tulanæ.

BIVALVE SHELLS.

Calceola. A regular bivalve shell, with unequal valves, the largest being in the form of a half sandal, and the smallest flat, semiorbicular, and resembling an operculum; the hinge with from one to three small teeth. This shell is only known as a fossil, and is considered by Gmelin as an Anomia (Anomia sandalium). It is very thick, and about an inch in length. Its back is flattened; its interior is striated longitudinally, and its valve or operculum, concentrically.

Terebratula, a regular bivalve shell, with unequal valves, fixing itself by a ligament or short tube; the largest valve perforated at its summit, which is prominent and recurved; hinge with two teeth. The regularity of the valves, the absence of any operculum, the position of the hole, and the form of the hinge, separate this genus from that of Anomia.

Crania, a regular bivalve shell, with unequal valves, the inferior almost smooth, and nearly round, and pierced in its internal face with three unequal and oblique holes; the superior valve very convex, furnished internally with two projecting cal losities. The three holes in the inferior valve of this shell, induced Lamarck and Bruguìere to separate it from the Anomiæ,

and place it in a distinct genus. The spe cies described by Linnæus is named by him Anomia craniolaris.

Placuna, an irregular bivalve flat shell; the interior hinge composed of two diverging ridges, which serve for the attachment of a ligament. Linnæus has arranged two species, Anomia placenta, and Anomia sella, under the genus Anomia.

Hyalæa, a regular bivalve shell, with unequal, bulging, connées, transparent valves, gaping under the beak, and tricuspidated at the base. This genus is formed by Lamarck, from a shell described by Forskal, and denominated in Gmelin's Linnæus Anomia tridentata, caudata and retusa. The Clio pyramidata of Linnæus are also referable to this genus.

Lingula, a long flat shell, formed of two valves, nearly equal, truncated in the forepart; the hinge without teeth; the beak of the valves pointed, and joined to a tendinous tube, which as a ligament to the shell, and fixes it to other solid bodies. Linnæus, who knew only of one valve of this shell, termed it Patilla unguis.

Corbula is an unequal-valved, sub-transverse, smooth, regular shell; with a conical cardinal tooth, curved, or turned upwards, on each valve; interior ligament, and two muscular impressions. This genus is characterised by the inequality of its valves, one of them being nearly a third larger than the other. These shells are found fossil at Grignon, near to Versailles.

Orbicula is a genus formed by Lamarck from a shell which was discovered by Muller, and which was named by him Patella anomala. Its differing so entirely from Patellæ in being a bivalve, and its being inhabited by an animal totally different from that of the Patella, has induced Lamarck thus to separate it from the genus Patella. This shell is orbicular, but rather flattened, and composed of two valves; by the lowest of which, which is extremely delicate, it adheres to other bodies. Its hinge is not known.

Pandora is a regular inequivalved, and inequilateral shell; with two cardinal, oblong, unequal, and diverging teeth, in the upper valve; and two oblong pits in the other valve; and interior ligament, and two muscular impressions. The shell which gives rise to this genus is Tellina inæquivalvis, of Linnæus; the inequality of the valves being the circumstance which is supposed to warrant the separation. This shell is named Pandora margaritacea, by Bruguìere.

Lima. An inequilateral-eared bivalve; the valves a little gaping on one side; hinge without teeth; ligament external, beaks separated. This genus is founded chiefly on the Ostrea lima of Linnæus, now named by Brugniere, Lima squamos. The separation of these shells from the Pectens, on the idea of their forming a byssus, whilst the Pectens do not, requires, it should seem, a more accurate knowledge of the habits of the animals which occupy the different

Pectens.

Pecten. This, contrary to Linnæus, is adopted by Bruguìere as a genus distinct from Ostrea. Its characters are given: a regular bivalve shell; the valves unequal; the hinge without teeth, most commonly eared, with a triangular pit for the ligament. The hinge shutting by a black ligament fixed in this triangular pit, and the different forms of the shells are the circumstances. which are supposed to warrant the proposed separation.

Pedum. The shell from which this genus has been formed, and of which only one species is known, being that which is figured by Chemnitz and Favanne, is semi-transparent, unequal valved, eared; the inferior valve gaping; the beaks separated; hinge without teeth; ligament external, and attached to a long and narrow gutter. The upper valve is striated, and granulated longitudinally; but the under valve is smooth, sharply edged, and hollowed out in one part.

Perna. An irregular, flattish, bivalve, shell: the hinge composed of many linear, parallel teeth, disposed in a straight line, across. The hinge is closed by a ligament which is attached between the teeth, and which, by its thickness, prevents the teeth from articulating with each other. Ostrea perna, isogona, ephippium, pictum, and legumen, of Linnæus, are placed under this genus.

Avicula. This genus Lamarck forms from Mytilus hirundo, Linnæus, which is the only shell in the genus. He describes it: an irregular, loose shell, a little gaping towards its beaks, and having the valves of unequal size. The hinge callous, without teeth; a little oblong pit, which is marginal and parallel with the edge which supports the ligament.

Malleus. The hammer-oyster of Linnæus, with two other species, form this genus, according to Lamarck, who gives for the characters of the genus: an irregular loose

shell, a little gaping near its beaks, having equal valves; a callous hinge, without teeth, having a conical pit, placed obliquely on the edge of each valve. This genus seems to be hardly sufficiently distinguishable from the last; nor does the name of the genus appear to be well adapted, since some of the species no ways resemble a hammer in their form.

Vulsella. This genus is formed from the Mya vulsella of Linnæus. The uncertainty with which this shell has been viewed, at different periods, shows the uncertainty of its nature, and the propriety of not placing it under any other genus. Linnæus had once considered it as a Pinna, and Bruguìere as an oyster. It is a loose shell, longitudinal, and nearly equivalved, terminating in a very short bent beak; the hinge callous, depressed, and without teeth, of equal elevation on each valve, forming a rounded conical pit for the ligament.

Ostrea. In this genus is comprehended those shells only which are oysters, according to common acceptation. The charac ters of the genus are, therefore, an irregular, adherent, inequivalve shell; the hinge without teeth; an oblong pit, sulcated across, giving attachment to a ligament.

Gryphæa. The shell, for the reception of which this genus was established by Lamarck, was improperly considered as a species of Anomia by Linnæus, and as a species of oyster by Bruguìere; to which latter genus it undoubtedly very nearly approximates. It is a loose unequivalved shell; the inferior valve concave, terminated by a beak turned upwards, and bent into an involved spire; the superior valve smaller, like an operculum; the hinge with out teeth, but with an oblong and dented pit; and one muscular impression in each valve. Lamarck enumerates eight fossil species of this genus.

Plicatula is a genus formed, by Lamarck, from Spondylus plicatus of Linnæus. It is an angulated shell, with unequal valves and unequal beaks, which are pointed; the edges are in deep plaits; its hinge is formed of two strong teeth on each valve, and an intermediate pit for the reception of the ligament; with one muscular impression ou each valve.

Spondylus. In this genus of Linnæus are comprised bivalve, irregularly-formed shells, the hinge of which is formed of two strong hooked teeth, and an intermediate pit for the ligament; in the inferior valve are two

thick recurved teeth, with two intermediate rounded cavities to receive the teeth of the other valve, and an elongated pit in which the ligament is placed; in the superior valve are two exterior cavities for receiving the teeth of the other valve, and two teeth curving backwards, with a pit for the ligament.

Chama. This gens is appointed, by Bruguiere and Lamarck, to those shells only which, in particular, possess unequal valves, and are adherent. The characters of the genus therefore are: a bivalve shell, with adhering unequal valves; the hinge compo. sed of one oblique thick tooth, which may be crenulated or rough, and is articulated in a cavity in the opposite valve.

It was necessary, therefore, to establish other genera for the reception of those shells which thus become excluded from the genus Chama. Hence Bruguìere formed too new genera; Cardita, having two teeth in the hinge; and Tridacna, possessing the same number, but having the edges of the crescent crenulated and gaping. Lamarck has proceeded still further; he has subdivided the genus Cardita from an isolated tooth, situated, in some species, under the corslet, as in Cardium isocardia, and makes this his genus Isocardia. He also makes another genus, Hippopus, the species of which are subtransverse, inequilateral shells; the hinge with two compressed, in verted teeth, the crescent filled up: of this genus is Chama gigax. But it is necessary still further to particularise these new genera.

Cardita, a loose inequilateral shell, the hinge with two teeth; the one at the base of the left valve, and the other longitudinal, parallel with the anterior face.

Hippopus. An inequilateral, subtransverse shell; the hinge with two compressed and inverted teeth; the crescent filled up. Hippopus, it is to be remembered, differs from Tridacna by having its crenate filled, whilst in Tridacna it is gaping.

Tridacna. An inequilateral, subtransverse shell; hinge with two teeth, compres sed and inverted; the crescent gaping. The Chama gigas of Linnæus (the Tridacna gigas of Lamarck) is the only species under this genus.

Cardium. This genus remains unaltered by the French naturalists. The characters being a sub cordiform shell, with valves dentated on their edges; the hinge with four teeth; two cardinal, approximating

obliquely in each valve, and articulating across with their correspondent teeth; the lateral teeth distant, and inverted in the opposite valve.

Acardo. Is a genus very properly established by Commercon. It is founded on two species: the generic characters of which are a shell composed of two, nearly equal, flat valves; having neither hinge nor ligament; a muscular impression appearing on the centre of each valve.

Radiolites. This is a genus approximating to the preceding, but very properly sepa rated from it by the form of the shell. The shell is of an irregular form, of unequal valves, striated on the outside; the inferior valve turbinated; the superior convex, or conical; no hinge nor ligament.

Erodona. This genus was formed, by Daudin, from two shells in the cabinet of Favannes. It is intermediate between the Mya and Mactra. It is a subtransverse, bivalve shell, irregular and gaping; one of the valves having a hollow tooth; and the other a pit between two projections; the ligament inserted on the tooth and in the pit.

Mya, is a transverse shell, gaping at both ends; the ligament on the inside; the left valve having a cardinal tooth, compressed, rounded, perpendicular to the valve, and giving attachment to the ligament. This is the original genus of Linnæus, from which Bruguìere and Lamarck have withdrawn many of the species to place them under the genera Vulsella, Glycemeris, and Unio; leaving only those sea-shells which have a very projecting cardinal tooth in one of their valves.

Glycemeris. A transverse shell, gaping at both extremities: a protuberant hinge without teeth; the ligament on the outer part. Such is Mya glycemeris of Linnæus.

Solen. A transverse shell, gaping at both extremities: the upper edge straight, or nearly so; two or three teeth at the hinge, furnished by both valves.

Tellina. Considerable confusion has arisen from the admission of species which by no means belong to this genus. Bruguìere and Lamarck have divided the Tel. lens of Linnæus into two new genera. 1. Tellina, a transverse or orbicular shell with equal valves, with a fold on the anterior side: one or two cardinal teeth, and two separated lateral teeth, as in Tellina virgata. 2. Caspa, a transverse shell, with

two teeth in one valve, and one tooth in the opposite valve, shutting between those of the other valve, as in Tellina angulata.

Cyclas. This genus comprehends some shells which Linnæus had associated with Tellens; but which Bruguìere and Lamarck have separated from them, from their wanting the fold on the anterior side. The characters are: A suborbicular, or in a small degree, transverse shell, without fold on the anterior side; the ligament external and bulging; two or three cardinal teeth, and elongated, lamelliform, inserted lateral teeth. They are fresh water shells.

Venus. This genus of Linnæus is formed by shells which are regular, suborbicular, bivalves, provided with a crescent and a corslet; three cardinal teeth near together, and sometimes one or two lateral teeth. The valves of this genus are generally pretty gibbous and thick; constantly equal, and nearly of a triangular form. Lamarck divides this genus into two. 1. Venus, a suborbicular or transverse shell, with three approximated cardinal teeth, the lateral ones being more or less diverging. 2. Meretrix, a transverse or orbicular shell; with three approximated cardinal teeth, and one isolated tooth under the crescent. The genus Caspa, mentioned above, is proposed by Bruguiere and Lamarck to comprise several of the Venus's of Linnæus.

Ungulina. A regularly formed long bivalve; the hinge formed by a very small tooth between two oblique deuts: the valves bearing the form of the finger nail. There is but one species in this genus. The hinge bears some resemblance to that of Cardium, but the general form of the shell differs much from that of Cardia.

Donax. A regular, transverse, inequilateral bivalve, with threes cardinal teeth, and one or two separated lateral teeth. Shells of this genus have much of the trian gular form, their sides very unequal; they are solid, thick, flattened at the inferior, and rounded at the opposite, extremity. The ligament, which, in most shells with equal valves, is placed above the summit, is in these shells unequally distributed above and below it. Above, it is narrow and short; and below, it is thick, nearly round, and fills the cavity of the corslet exactly.

Mactra. A bivalve shell, regular, transverse, inequilateral, and a little gaping, the eardinal tooth having a pit for the ligament; lateral teeth compressed and inserted, or

none.

Lamarck divides this genus into three.

1. Mactra, a transverse, inequilateral shel a little gaping; the cardinal tooth folded in a furrow, articulating with that of the opposite valve, and accompanying a pit for the ligament; two lateral and inserted teeth, such is Mactra stultorum. 2. Lutraria, a transverse, inequilateral shell, gaping at the extremities; two cardinal teeth, oblique, and diverging, accompanying a large pit for the ligament; no lateral teeth; such is Mactra lutraria, Linnæus. 3. Paphia, a subtransverse, inequilateral shell, the valves close: a pit for the ligament on the beak between or near to the teeth of the hinge, as in Venus divaricata. Linnæus.

Crassatella. A genus formed by Lamarck of shells unknown to Linnæus, and which Brugnìere had placed in the genus Mactra. The generic chararacters are an inequilateral, subtranverse shell, with close valves, with a sunk crescent or corslet; the ligament internal; the pit for the ligament placed under the beaks, above the teeth of the hinge. There are two fossil, and one recent species under this genus. These shells are remarkable for the thickness of the valves, and for their two deep muscular impressions.

Trigonia. This is a genus formed by Lamarck, the species of which are known only in a fossil state. The characters of the genus are, an inequilateral subtrigonal shell, the hinge formed by two large flat diverging teeth, transversely grooved. These are the Cunei of Dacosta.

Hiatella. A genus formed by Daudin on two shells from Tranquebar, which appear to be intermediate between the genera Trigonia and Tridacna; the characters are a transverse, irregular bivalve shell, gaping in its superior edge; its hinge a tooth in each valve, inserted in a groove in the opposite valve.

Cucullæa. A gibbous, subtranverse inequilateral shell, with detached beaks: the hinge in a straight line, having a range of numerous teeth, transverse inserted; and at the extremities two or three parallel rib-like teeth, the ligaments external. This genus is founded by Lamarck on a recent shell from the Indian Sea, and on a fossil shell from Beauvais, which Bruguìere had placed among the Arks; from which these shells differ in the ribs placed at the extremities of the hinge.

Arca. An inequilateral bivalve shell; the hinge composed of numerous teeth, which lock in the interstices of those of the opposite valve, and which range in a straight, angular, or curved line. The ligament

tulanæ.

BIVALVE SHells.

Calceola. A regular bivalve shell, with unequal valves, the largest being in the form of a half sandal, and the smallest flat, semiorbicular, and resembling an operculum; the hinge with from one to three small teeth. This shell is only known as a fossil, and is considered by Gmelin as an Anomia (Anomia sandalium). It is very thick, and about an inch in length. Its back is flattened; its interior is striated longitudinally, and its valve or operculum, concentrically.

Terebratula, a regular bivalve shell, with unequal valves, fixing itself by a ligament or short tube; the largest valve perforated at its summit, which is prominent and recurved; hinge with two teeth. The regularity of the valves, the absence of any operculum, the position of the hole, and the form of the hinge, separate this genus from that of Anomia.

Crania, a regular bivalve shell, with un equal valves, the inferior almost smooth, and nearly round, and pierced in its internal face with three unequal and oblique holes; the superior valve very convex, furnished internally with two projecting cal. losities. The three holes in the inferior valve of this shell, induced Lamarck and Bruguìere to separate it from the Anomiæ,

and place it in a distinct genus. The spe cies described by Linnæus is named by him Anomia craniolaris.

Placuna, an irregular bivalve flat shell; the interior hinge composed of two diverging ridges, which serve for the attachment of a ligament. Linnæus has arranged two species, Anomia placenta, and Anomia sella, under the genus Anomia.

Hyalæa, a regular bivalve shell, with unequal, bulging, connées, transparent valves, gaping under the beak, and tricuspidated at the base. This genus is formed by Lamarck, from a shell described by For skal, and denominated in Gmelin's Linnæus Anomia tridentata, caudata and retusa. The Clio pyramidata of Linnæus are also referable to this genus.

Lingula, a long flat shell, formed of two valves, nearly equal, truncated in the forepart; the hinge without teeth; the beak of the valves pointed, and joined to a tendinous tube, which as a ligament to the shell, and fixes it to other solid bodies. Linnæus, who knew only of one valve of this shell, termed it Patilla unguis.

Corbula is an unequal-valved, sub-transverse, smooth, regular shell; with a conical cardinal tooth, curved, or turned upwards, on each valve; interior ligament, and two muscular impressions. This genus is characterised by the inequality of its valves, one of them being nearly a third larger than the other. These shells are found fossil at Grignon, near to Versailles.

Orbicula is a genus formed by Lamarck from a shell which was discovered by Muller, and which was named by him Patella anomala. Its differing so entirely from Patellæ in being a bivalve, and its being inhabited by an animal totally different from that of the Patella, has induced Lamarck thus to separate it from the genus Patella. This shell is orbicular, but rather flattened, and composed of two valves; by the lowest of which, which is extremely delicate, it adheres to other bodies. Its hinge is not known.

Pandora is a regular inequivalved, and inequilateral shell; with two cardinal, oblong, unequal, and diverging teeth, in the upper valve; and two oblong pits in the other valve; and interior ligament, and two muscular impressions. The shell which gives rise to this genus is Tellina inæquivalvis, of Linnæus; the inequality of the valves b ing the circumstance which is suppo warrant the separation. This shell Pandora margaritacea, by Brugur