Chapter C: MARINÆ. Four genera (1)

4. Cyprina. Two species.

This shell is generally large, resembling the Venus, from which it may be distinguished by having on the front side one impressed lateral tooth, which is sometimes obsolete; the nymphæ or callosities of the hinge large, arched, and terminated near the apices by a cavity, sometimes very deep.

De Blainville says that this genus is intermediary to the Cyclas and the Venus, and contains but one living species; Lamarck makes two, though at first he characterized eight.

Cyprina tennistria.
Cyprina Islandica.

_C. Islandica._ The Icelandic Cyprina. Pl. 9, fig. 2.

Shell thick, regular, heart-shaped, covered with dark brown epidermis; white interior; sub-striated longitudinally; apices very strongly recurved anteriorly, and often contiguous; hinge thick, sub-similar, formed by three cardinal teeth but little convergent, and by one remote posterior lateral tooth, sometimes obsolete; ligament very thick, convex, fixed to large, arched, nymphal callosities, preceded by a cavity more or less deep, hollowed immediately behind the summits; muscular impressions subcircular and very distant.

5. Cytherea. Seventy-eight species.

This genus was taken from the Venus, and is easily defined as distinct from it by having four primary teeth on one valve, and only three united on the other, with an isolated cavity, oval and parallel to the margin; the lateral teeth divergent to the summit. In some species the internal margin is entire, having the anterior cardinal tooth with a striated canal or uneven sides; in others the anterior cardinal tooth is entire, without a striated canal; sometimes the internal margin is crenulated or dentated.

Shell solid, regular, equivalve, inequilateral; apices equal, recurved, and slightly projecting; four primary teeth on one valve, of which three are divergent and approximating at the base, and one remote; three primary divergent teeth on the other valve, with a distant cavity parallel to the edge.

Cytherea lusoria.
C. petechialis.
C. impudica.
C. castanea.
C. zonaria.
C. graphica.
C. morphina.
C. purpurata.
C. casta.
C. corbicula.
C. meretrix.
C. gigantea.
C. erycina.
C. lilacina.
C. impar.
C. erycinella.
C. pectoralis.
C. planatella.
C. florida.
C. nitidula.
C. Chione.
C. maculata.
C. citrina.
C. albina.
C. lata.
C. mactroides.
C. trigonella.
C. sulcatina.
C. Hebræa.
C. castrensis.
C. ornata.
C. picta.
C. tigrina.
C. scripta.
C. numulina.
C. muscaria.
C. pectinata.
C. gibbia.
C. ranella.
C. testudinalis.
C. divaricata.
C. cuneata.
C. placunella.
C. rugifera.
C. tripla.
C. Venetiana.
C. juvenilis.
C. rufa.
C. Guiniensis.
C. Dione.
C. Arabica.
C. trimaculata.
C. immaculata.
C. pellucida.
C. hepatica.
C. lucinalis.
C. lactea.
C. exoleta.
C. lincta.
C. concentrica.
C. prostrata.
C. interrupta.
C. tigerina.
C. punctata.
C. umbonella.
C. undatina.
C. pulicaris.
C. mixta.
C. abbreviata.
C. plicatina.
C. flexuosa.
C. macrodon.
C. lunularis.
C. squamosa.
C. lunaris.
C. cardilla.
C. cygnus.
C. dentaria.

_C. Chione._ The Chione Cytherea.

Thick, solid, heart-shaped, covered with a smooth brown epidermis, beneath which the shell is of a beautiful purple; radiated longitudinally, faintly wrinkled transversely, anterior cardinal tooth entire, and without a striated canal; apex turned sideways, with a cordiform depression.

_C. mactroides._ The Mactra-like Cytherea. Pl. 9, fig. 4.

Species thin, convex, triangular; summits very marked; margins sharp; anterior cardinal tooth entire.

_C. pectinata._ The pectinated Cytherea.

Species oval, thick, solid, more or less compressed, costated, pectinated upon the edges.

6. Venus. Eighty-eight species.

This genus of shells is numerous and varied. It surpasses all bivalve shells in beauty, and is in form very like the Cytherea, but easily distinguished by the hinge, which almost invariably contains three approximate teeth, and a lateral tooth diverging to the summit. The internal margin of the valves is crenated or dentated, with or without lamellar striæ.

The shells are of the most beautiful and lively tints; the exterior as well as the interior colouring is of almost every possible shade and hue. They are found buried a little below the surface on the sandy shores of most parts of the world, particularly in warm climates.

Shell solid, thick, regular, perfectly equivalve and close, more or less inequilateral; summits well marked, inclined anteriorly; hinge sub-similar; the middle cardinal tooth forked, or three cardinal teeth more or less contiguous and convergent towards the summit; ligament thick, often arched, convex, and exterior; two distant muscular impressions; cordiform depressions beneath the beaks.

Venus puerpera.
V. reticulata.
V. pygmæa.
V. corbis.
V. verrucosa.
V. rugosa.
V. casina.
V. crebiscula.
V. crenulata.
V. discina.
V. granulata.
V. marica.
V. cingulata.
V. cardivides.
V. grisea.
V. elliptica.
V. Dombeii.
V. mercenaria.
V. lagopus.
V. gallina.
V. gallinula.
V. pectinula.
V. sulcata.
V. lamellata.
V. exalbida.
V. rufa.
V. dorsata.
V. hiantina.
V. crassisulca.
V. corrugata.
V. Malabarica.
V. papilionacea.
V. adspersa.
V. punctifera.
V. turgida.
V. literata.
V. florida.
V. petalina.
V. bicolor.
V. floridella.
V. catenifera.
V. pulchella.
V. sinuosa.
V. tristis.
V. plicata.
V. cancellata.
V. pectorina.
V. sulcaria.
V. textilis.
V. texturata.
V. geographica.
V. rariflamma.
V. decussata.
V. pullastra.
V. glandina.
V. truncata.
V. retifera.
V. anomala.
V. galactites.
V. exilis.
V. scalarina.
V. Scotica.
V. aurea.
V. virginea.
V. marmorata.
V. ovulæa.
V. laterisulca.
V. callipyga.
V. opima.
V. nebulosa.
V. phaseolina.
V. carneola.
V. flammiculata.
V. conularis.
V. strigosa.
V. aphrodina.
V. Perronii.
V. aphrodinoides.
V. elegantina.
V. flammea.
V. rimularis.
V. vulvina.
V. vermiculosa.
V. subrostrata.
V. undulosa.
V. pumila.
V. ovata.
V. inquinata.

_V. Casina._ The Casina, or broad-ribbed Venus. Pl. 8, fig. 2.

Sub-orbicular, with transversely acute recurved ridges; lamellar striæ; crenulated on the hind margin; slightly channelled behind the depression.

_V. decussata._ The intersected Venus. Pl. 9, fig. 3.

Species sub-rhomboidal, with decussated striæ; margin not denticulated; umbo placed near one end; the three teeth of the hinge very contiguous and very weak; exterior brownish and marked with purple lines.

_V. aurea._ The golden Venus.

Sub-orbicular, inequilateral, transversely and concentrically striated; yellow golden colour.

_V. corbis._ The basket Venus.

Species sub-rhomboidal, deeply latticed; teeth very thick, ligament entirely concealed, margin dentated.

_V. puerpera._ The convex or spotted Venus.

Species thick, solid, orbicular or sub-orbicular, with concentric striæ, or, rather, laminæ; teeth very thick; margin dentated.

_V. granulata._ The granulated Venus.

Species thick, solid, cardium-shaped, radiated from the summit to the base.

7. Venericardia. One species.

This genus resembles the Venus, but has only two oblique cardinal teeth on each valve.

Shell equivalve, inequilateral, sub-orbicular, sides generally with longitudinal rayed ribs; hinge with two oblique cardinal teeth in each valve, turned in the same direction.

_V. imbricata._ The imbricated Venericardia. Pl. 9, fig. 1.

Species almost round, having convex longitudinal ribs, covered with imbricated rough scales; inferior margin rounded and dentated; more and more equilateral; the two teeth short and oblique.

FAMILY X.
CARDIACEA. Five genera.

1. Cardium. Cockle, or Heart Shell. Forty-eight species.

This genus received its name from its resemblance to a heart (καρδια). It is so well defined by Linnæus that no alteration was made by Lamarck, except in making two divisions of them; the first distinguished by having the anterior side as large or larger than the posterior, and no distinct angle at the apex; the second by possessing carinated or angular umbones, and the posterior side often much larger than the anterior. These shells are found at a small depth in the sand on almost every seashore.

Shell inflated, equivalve, sub-cordiform (when seen anteriorly), generally costated from the summit to the circumference; summits very evident; slightly recurved forward; hinge complex, similar, formed by two oblique cardinal teeth, articulating with the corresponding teeth on the other valve; two distant lateral teeth on each valve; ligament dorsal, posterior, and very short.

Cardium costatum.
C. Indicum.
C. ringens.
C. Asiaticum.
C. tennicostatum.
C. fimbriatum.
C. pseudolima.
C. aculeatum.
C. erinaceum.
C. tuberculatum.
C. Brasilianum.
C. apertum.
C. papyraceum.
C. bullatum.
C. ciliare.
C. echinatum.
C. lævigatum.
C. biradiatum.
C. eolicum.
C. pectinatum.
C. isocardia.
C. muricatum.
C. angulatum.
C. marmoreum.
C. elongatum.
C. ventricosum.
C. rugosum.
C. sulcatum.
C. serratum.
C. unedo.
C. medium.
C. fragum.
C. retusum.
C. tumoriferum.
C. rusticum.
C. edule.
C. Groenlandicum.
C. latum.
C. crenulatum.
C. exiguum.
C. minutum.
C. roseum.
C. scobinatum.
C. hemicardium.
C. cardissa.
C. inversum.
C. Junoniæ.
C. lineatum.

_C. edule._ The edible Cardium, or common Cockle. Pl. 10, fig. 2.

Species not gaping, with about twenty-six depressed ribs and transverse obsolete scales; of a cream colour; beaks protuberant.

_C. cardissa._ Venus’s Heart.

Species heart-shaped, valves angularly flattened, umbones alternating.

_C. lævigatum._ The smooth Cardium.

Species smooth or nearly so, anterior side as large as the posterior.

_C. hemicardium._ The half-heart Cardium.

Species ribbed, with elevated rough striæ; the anterior side is very short and almost flat.

_C. costatum._ The high-ribbed Cardium.

No angle at the umbones; anterior side at least as large as the posterior; rows of white, hollow, elevated ribs, situated at regular distances, proceeding from the umbones to the margin, with the spaces between them of a reddish brown colour.

_C. unedo._ The Strawberry Heart.

Species with ribs armed with small crescent-shaped scales.

_C. tuberculatum._ The tuberculated Cardium.

Species not gaping, with large ribs armed with nodules.

2. Cardita. Twenty-one species.

Lamarck took this genus from the Chama on account of several peculiarities in the shell as well as in the animal. It is not affixed to other bodies by its lower valve, but, according to De Blainville, lies exposed on the rocks. There is some difficulty in distinguishing this genus from the Venericardia, without carefully examining the position of the two teeth.

Shell regular, thick, solid, equivalve, more or less inequilateral; summit dorsal, always very recurved anteriorly; hinge similar, formed by two oblique teeth; one short cardinal placed beneath the umbo, the other oblique, arched, marginal, and prolonged; ligament elongated, sub-exterior, and inserted; two very distinct muscular impressions.

Cardita sulcata.
C. ajar.
C. turgida.
C. squamosa.
C. phrenetica.
C. crassicosta.
C. rufescens.
C. calyculata.
C. subaspera.
C. nodulosa.
C. intermedia.
C. trepezia.
C. bicolor.
C. depressa.
C. concamerata.
C. sinuata.
C. aviculina.
C. citrina.
C. sublævigata.
C. corbularis.
C. lithophagella.

_C. crassicosta._ The thick-ribbed Cardita.

Species elongated, a little gaping at the inferior margin; ligament concealed.

_C. sulcata._ The furrowed Cardita. Pl. 10, fig. 3.

Sub-cordiform or oval, more transverse than longitudinal; colour white, tesselated with brown; posterior depression heart-shaped; longitudinal, convex, transversely-striated ribs.

3. Cypricardia. Four species.

Distinguished from the Cardita by having three teeth beneath the apices, and a callous lengthened tooth or ridge.

Shell obliquely elongated, equivalve, inequilateral; valves striated, but never ribbed; hinge with three teeth beneath the umbo, and one lateral elongated tooth.

Cypricardia Guinaica.
C. angulata.
C. rostrata.
C. coralliophaga.

_C. Guinaica._ The Guinea Cypricardia. Pl. 10, fig. 6.

Species elongated, very inequilateral; summit rounded and recurved anteriorly; two short divergent cardinal teeth, besides a lamellous tooth; ligament very long, projecting or not; yellowish white, covered with decussated striæ.

4. Hiatella. Two species.

Established by Daudin; classed by Linnæus with the Solen, but Lamarck is of opinion that it more nearly approximates the Cardita.

Shell thin, sub-rhomboidal, equivalve, very inequilateral, gaping at its inferior margin and posterior extremity; the summit very anterior and recurved in front; dorsal hinge formed by a single tooth on one valve corresponding to a semicircular slope on the opposite valve, or by a small tooth with a cardinal cavity in each valve; ligament probably exterior and dorsal; muscular impressions unknown.

Hiatella Arctica.
Hiatella biaperta.

_H. Arctica._ The Arctic Hiatella.

Shell small, transversely oblong; apices truncated, with two divergent spring ridges; a small tooth on each valve; cream colour, with decussated striæ; inside pearly.

_H. biaperta._ The double-clefted Hiatella. Pl. 10, fig. 4.

Species that has only a single tooth on one valve; yellowish white.

5. Isocardia. Three species.

Taken from the Chama of Linnæus on account of a peculiarity in the shape of the cardinal teeth, and the singular curvature of the umbones.

Isocardia cor.
I. semisulcata.
I. Moltkiana.

_I. cor._ The heart Isocardia. Pl. 12, fig. 4.

Shell free, regular, heart-shaped, equivalve, very inequilateral; summits diverging, strongly recurved spirally, forward, and outward; hinge dorsal, long, similar, formed by two flat cardinal teeth, with an elongated lateral one behind the ligament, which is dorsal and exterior, diverging towards the summits; muscular impressions very distinct and rather small; slightly wrinkled longitudinally; exterior reddish chestnut colour, interior white.

The Isocardia Moltkiana is a very rare shell, and the most elegant species of this genus.

FAMILY XI.
ARCACEA. Four genera.

1. Cucullæa. One species.

Distinguished from the Arca by the muscular impression within, to one side of which is an ear-shaped testaceous appendage; the shell is more trapeziform, and the hinge by age becomes obsolete, giving the teeth a more horizontal appearance.

Shell equivalve, inequilateral, trapeziform, heart-shaped; beaks distant, and separated by the angular groove of the ligament, which is altogether external; hinge linear, straight, with small transverse teeth, having at its extremity from two to five parallel ribs; valves marked with minute and strong longitudinal striæ, and sometimes one valve overlaps; margins crenulated.

_C. auriculifera._ The eared Cucullæa. Pl. 10, fig. 1.

Species navicular or obliquely heart-shaped, with decussated striæ; hinge completely straight, with two parallel ribs at each end, the terminal teeth longer and more oblique than the others; exterior chestnut colour, interior white, tinged with violet.

2. Arca. The Ark. Thirty-seven species.

This genus is easily known by its resemblance to the hull of a ship; the hinge is peculiar, being composed of numerous sharp teeth alternately inserted between each other. The Arca of Linnæus was divided by Lamarck into the four genera that compose this family, each possessing a strong distinctive character. All the shells of this family are found in the sea at a little distance from the shore; they are covered with a dark greenish lamellar or velvet-like epidermis, frequently ending in a deep fringe at the margin.

Shell a little varied in form, but most generally elongated, and more or less oblique at the posterior extremity; sometimes very inequilateral; summits more or less distant, and a little recurved forward; hinge anomalous, straight, or a little curved; long, and formed by a line of short vertical teeth decreasing from the extremities to the centre; ligament exterior, broad; sometimes the margin is crenated.

Arca tortuosa.
A. semitorta.
A. Noæ.
A. tetragona.
A. umbonata.
A. sinuata.
A. avellana.
A. cardissa.
A. ventricosa.
A. retusa.
A. sulcata.
A. ovata.
A. Helbingii.
A. scapha.
A. barbata.
A. fusca.
A. Magellanica.
A. Domingensis.
A. lactea.
A. trapezina.
A. pistachia.
A. pisolina.
A. cancellaria.
A. callifera.
A. irudina.
A. bisulcata.
A. Indica.
A. senilis.
A. antiquata.
A. rhombea.
A. granosa.
A. auriculata.
A. Brasiliana.
A. corbicula.
A. squamosa.
A. Cayennensis.
A. inequivalvis.

_A. Noæ._ Noah’s Ark. Pl. 10, fig. 5.

Species boat-shaped, oblong, striated transversely and ribbed longitudinally; umbones remote and incurvated; margins entire and gaping; hinge straight; whitish, with divergent zigzag chestnut stripes; inside bluish white.

_A. tortuosa._ The twisted Ark.

A rare species; shell elongated, close, twisted; hinge completely straight.

_A. barbata._ The bearded Ark.

Species with the hinge straight, not hollowed or not gaping inferiorly, and of which the muscle is not adherent.

3. Pectunculus. Nineteen species.

This genus has the ligament partially inserted internally, and has no exterior angular groove. The valves never gape, often have rayed longitudinal ribs, are compressed, and the shell by age becomes thick and ponderous, sometimes attaining a large size. The teeth in the hinge are not so numerous as in the Arca and Cucullæa; the centre teeth appear worn down.

Shell close, orbicular, doubly convex, equivalve, sub-equilateral; summits almost vertical, and more or less distant; hinge formed on each valve by a rather numerous series of small teeth, disposed in a curved line, sometimes broken under the summit; ligament external and large.

Pectunculus glycimeris.
P. pilosus.
P. undulatus.
P. marmoratus.
P. scriptus.
P. angulatus
P. stellatus.
P. pallens.
P. violacescens.
P. zonalis.
P. pennaceus.
P. rubens.
P. castaneus.
P. pectiniformis.
P. striatularis.
P. nummarius.
P. pectinatus.
P. radians.
P. vitreus.

_P. glycimeris._ The delicious Pectunculus.

Sub-orbicular, umbones produced; finely striated transversely and longitudinally; covered with epidermis, under which it is marked with reddish chestnut spots or bands; inside white; margins crenulated.

_P. pilosus._ The hairy Pectunculus.

Species convex, more or less smooth and hairy.

_P. pectiniformis._ The Pecten-shaped Pectunculus. Pl. 11, fig. 6.

Species lenticular, more compressed, pectinated, and more or less rough.

4. Nucula. Six species.

Shell small, more or less thick, sub-triangular, equivalve, inequilateral; summits contiguous and turned forward; hinge similar, formed by a numerous series of very pointed teeth, pectinated and disposed in a line interrupted under the summit; ligament internal, short, inserted in a small oblique cavity in each valve; two muscular impressions; valves more or less pearly within.

Nucula lanceolata.
N. rostrata.
N. pella.
N. Nicobarica.
N. obliqua.
N. margaritacea.

_N. rostrata._ The beaked Nucula.

Species of which the margin is entire.

_N. margaritacea._ The pearly Nucula. Pl. 11, fig. 7.

Species of which the margin is crenated; numerous regular pectinated teeth; obliquely ovate, trigonal; striæ minute and almost obsolete; covered with a greenish epidermis; inside silvery, pearl-like.

FAMILY XII.
TRIGONACEA. Two genera.

1. Trigonia. One species.

Supposed to be in very deep places in the sea; it is a strong, beautiful, pearly shell, sub-trigonal or sub-orbicular; thick, regular, equivalve, inequilateral; summits slightly prominent, recurved, anterodorsal; hinge complex, dorsal, dissimilar; two large oblong teeth laterally compressed, joined angularly under the summit, strongly furrowed on the right valve, penetrating into two excavations of the same form, equally furrowed on the left valve; ligament exterior and marginal; two distinct muscular impressions.

_T. pectinata._ The pectinated Trigonia. Pl. 11, fig. 4.

Species sub-orbicular, with radiated or divergent, prominent, and somewhat scaly ribs; inside pearly; margin crenellated.

2. Castalia. One species.

This genus is found in fresh waters, and differs from the Trigonia in the number and position of the lamellar teeth. The substance of the shell is pearly.

Shell sub-trigonal, equivalve, inequilateral; umbones eroded, covered with epidermis, and inflected anteriorly; hinge with two lamellar teeth, transversely striated, one of them posterior, distant, and shortened, the other anterior, lengthened, and lateral; ligament exterior.

_C. ambigua._ The ambiguous Castalia. Pl. 11, fig. 5.

Short, sub-trigonal; umbones truncated; longitudinally ribbed, with distant transverse striæ; covered with epidermis, under which the shell is of a pale chestnut brown, inside pearly; the lamellar and præ-apicial teeth are well marked, more regular, and all striated perpendicular to their length.

FAMILY XIII.
NAIADES. Four genera.

1. Unio. Forty-eight species.

The species of this genus become every day more numerous; they are found in all countries, but particularly in North America. The Unio is a fresh-water shell, and therefore, with great propriety, removed from the Mya, which consists entirely of marine shells. The substance is pearly; the exterior covered with a brown or green epidermis; the apices eroded. They are found in the mud of rivers, with their apices downward; some are slightly gaping, and some species produce fine pearls.

Shell generally very thick, pearly within, covered with epidermis; summits eroded, dorsal, and sub-interior; besides a long lamellous tooth under the ligament, the hinge is formed by a double precardinal tooth, more or less compressed, and dentated irregularly on the left valve, simple on the right valve; ligament external, dorsal, and post-apicial; muscular impressions well marked.

Unio sinuata.
U. elongata.
U. crassidens.
U. Peruviana.
U. rariplicata.
U. pupurata.
U. ligamentina.
U. obliqua.
U. retusa.
U. rarisulcata.
U. coarctata.
U. purpurascens.
U. radiata.
U. brevialis.
U. rhombula.
U. carinifera.
U. Georgina.
U. clava.
U. recta.
U. naviformis.
U. glabrata.
U. nasuta.
U. ovata.
U. rotundata.
U. littoralis.
U. semirugata.
U. nana.
U. alata.
U. deladonta.
U. sulcidens.
U. rostrata.
U. pictorum.
U. Batava.
U. corrugata.
U. nodulosa.
U. varicosa.
U. granosa.
U. depressa.
U. Virginianum.
U. luteola.
U. marginalis.
U. angusta.
U. manca.
U. cariosa.
U. spuria.
U. Australis.
U. anodontina.
U. sub-orbiculata.

_U. pictorum._ The Painter’s Unio. Pl. 8, fig. 6.

Species oval, not auriculated, strong, anterior side rhomboid and attenuated; the opposite side obtusely acute; the umbones somewhat warted; concentrically wrinkled; covered with a dusky green epidermis.

_U. sinuata._ The crooked Unio.

Species oval, sub-auriculated; cardinal tooth short, not lamellar or sub-striated.

_U. sub-orbiculata._ The sub-orbicular Unio.

Species round or almost round; cardinal tooth compressed, elongated, and often lamellar.

2. Hyria. Two species.

Easily distinguished from the Unio by a compound cardinal tooth, which slopes in an inclined position towards the posterior side. They are more found in lakes than in rivers.

Shell solid, pearly, equivalve, obliquely triangular, auriculated; base truncated and straight; hinge with two projecting teeth; the cardinal divided into numerous divergent parts; anterior ones smaller, the others long and lamellar.

Hyria avicularis.
Hyria corrugata.

_H. avicularis._ The little bird Hyria. Pl. 5, fig. 4.

Umbones smooth and polished; ears large, with pointed terminations; finely striated; interior pearly, exterior of a rich reddish golden-yellow colour; covered with a greenish brown epidermis.

3. Anodonta. Fifteen species.

A fresh-water shell, found in ponds and lakes, difficult to be distinguished from the Unio but by the hinge, which wants the cardinal and lateral tooth, and merely presents a smooth internal rim round the edge terminated by a sinus or notch, in which the anterior extremity of the ligament is sunk; the substance is pearly, covered with a false epidermis.

Shell ordinarily rather thin, regular, close, equivalve, inequilateral; summit anterodorsal; hinge linear, without teeth; ligament external, dorsal, and post-apicial; two well-marked muscular impressions.

Anodonta cygnæa.
A. anatina.
A. sulcata.
A. fragilis.
A. cataracta.
A. trapezialis.
A. exotica.
A. rubens.
A. crispata.
A. uniopsis.
A. Pennsylvanica.
A. intermedia.
A. glauca.
A. sinuosa.
A. Patagonica.

_A. cygnæa._ The Swan Anodonta. Pl. 11, fig. 2.

Species oval, thin, elongated, hinge straight, and only auriculated anteriorly; beaks small and ventricose; concentrically wrinkled; covered with a greenish epidermis, which is frequently of a brown tinge towards the umbo.

_A. rubens._ The ruddy Anodonta.

Species oval, hinge arched, without trace of auricula or ear.

_A. trapezialis._ The trapezium Anodonta. Pl. 11, fig. 3. Species oval or rounded, auriculated on both sides the summit.

4. Iridina. One species.

A very rare shell, separated from the Anodonta on account of the hinge being attenuated in the middle, and having small tubercles distributed along its length. The substance is thicker and more solid than the Anodonta, and of a brilliant rose-coloured pearly hue; it is found in the rivers of warm countries.

Shell equivalve, inequilateral, transverse, with small apices; recurved, but nearly erect; not auriculated; hinge very long, linear, crenulated through all its length; ligament external and marginal; two well-marked muscular impressions.

_I. exotica._ The exotic Iridina.

The only species of this genus answering to the above description.

FAMILY XIV.
CHAMACEA. Three genera.

1. Diceras. One fossil species.

Only found in a fossil state; distinguished from the Chama by the hinge, which is dissimilar, formed by a large thick tooth, concave in the greater valve; summits very projecting; almost regular spiral contortions.

_D. arietina._ The ram’s-horn Diceras.

Shell irregular, inequivalve, inequilateral, somewhat heart-shaped, with divergent beaks.

2. Chama. The Clam or Gaper. Seventeen species.

In this genus are now comprehended only such as have a thick oblique transverse tooth, resembling a lengthened callosity, generally crenulated or grooved, fitting into a corresponding cavity in the lower valve. The animals inhabiting these shells have the faculty of affixing themselves to other bodies by the lower valve.

The Chama received its name from its gaping; it is found in most seas, particularly in the Southern; sometimes its colours are elegantly blended.

Shell irregular, adherent, inequivalve, inequilateral; summits more or less twisted spirally, especially in the lower valve; some from left to right, others from right to left; hinge dissimilar, large, formed by one lamellous, arched, sub-crenulated, post-cardinal tooth, articulating into a furrow of the same form; exterior, post-apicial, slightly inserted; two large and rather distant muscular impressions.

Chama Lazarus.
C. damæcornis.
C. gryphoides.
C. crenulata.
C. unicornis,
C. arcinella.
C. radians.
C. cristella.
C. florida.
C. limbula.
C. æruginosa.
C. asperella.
C. decussata.
C. albida.
C. ruderalis.
C. croceata.
C. Japonica.

_C. Lazarus._ Lazarus’s Chama. Pl. 12, fig. 2.

Species of which the summits twist from left to right; imbricated, dilated, waved foliations; striated obsoletely; exterior white, orange, red, or yellow; interior white.

_C. arcinella._ The hedgehog Chama.

Species of which the summits twist from right to left; the pink-coloured ones of this species are the most prized.

3. Etheria. Four species.

Distinguished from the Chama by the want of teeth in the hinge, and being of a pearly substance. It is a rare shell, only found in deep water, where it is attached to the rocks by the lower valve. Its irregular form is perhaps occasioned by the lower valve adapting itself to the form of the body to which it is affixed. Two species are fluviatile and two marine.

Shell adhering, irregular, thick, pearly, inequivalve, inequilateral; summits thick, little evident; hinge toothless, callous, thick, irregular; longitudinal, sub-dorsal ligament, partly exterior and partly penetrating into the shell; two oblong muscular impressions, one inferior and anterior, the other superior and sub-posterior; with or without an oblong incrusted callosity on the base of the valve.

Etheria elliptica.
E. semilunata.
E. trigonula.
E. transversa.

_E. elliptica._ The oval Etheria. Pl. 11, fig. 1.

Species with an oblong callosity on the anterior part of the shell; oval, depressed, dilated towards the umbones; summits distant.

_E. semilunata._ The semilunar Etheria.

Species without callosity at the base.

FAMILY XV.
TRIDACNITES. Two genera.

1. Tridacna. The Clam Shell. Six species.

The most ponderous shell known, sometimes measuring several feet in length, and sometimes weighing five hundred pounds.

By Linnæus this genus was classed with the Chama, but the characteristic distinctions are so great that they are easily known. The Chama is irregular, has but one tooth, and is fastened to other substances by the lower valve; the Tridacna is equivalve, has but two teeth, and is affixed to other bodies by a byssus consisting of filiform tendons.

The animal inhabiting this shell is said to produce very fine pearls, but there is no pearly appearance on the valves.

Shell thick, solid, varying in size; some are very small and some very large; regular, triangular, more or less inequilateral; the summits inclined backward; hinge dissimilar, entirely anterior to the summits; one lamellous precardinal tooth, and two distant lateral teeth on the left valve, corresponding to two lamellous precardinal teeth and one remote lateral tooth in the right valve; ligament anterior, elongated; one forked sub-median muscular impression, almost marginal and oftentimes nearly obsolete; valves with broad, rounded longitudinal ribs, armed with vaulted scales, more or less elevated; posterior slope heart-shaped, and widely gaping.

Tridacna gigas.
T. elongata.
T. squamosa.
T. crocea.
T. mutica.
T. serrifera.

_T. gigas._ The giant Tridacna. Pl. 12, fig. 3.

Species of which the shell is sometimes very large, white, transversely ovate or elongated; the anterior side longer than the posterior; broad ribs covered with vaulted scales; when of a pink or orange colour, greatly valued.

2. Hippopus. One species.

Similar to the Tridacna, but distinguished from it by having its posterior slope closed with a dentated margin; its ribs are never arched or vaulted, and its anterior side is shorter than the posterior side.

_H. maculatus._ The spotted Hippopus. Pl. 12, fig. 1.

Shell transversely ovate, ventricose, with scaly ribs; lunule, heart-shaped, and oblique; margins deeply crenulated; reddish purple spots.

FAMILY XVI.
MYTILACEA. Three genera.

1. Mytilus. The Muscle. Thirty-five species.

As arranged by Lamarck, now comprises only such shells as are regular, equivalve, and longitudinal; solid in substance, and attached to other bodies by a short thick byssus.

In colour and appearance they greatly vary, some being smooth and beautifully variegated with delicate colours, or radiated with purple and white; some are coarsely ribbed or granulated, and have only one colour, as black, blue, yellow, brown, or green; all are covered with an epidermis, to which oftentimes the colour is confined.

Shell of a close texture, elongated, more or less oval, sometimes sub-triangular, equivalve, summits anterior, more or less curved, a little sloping inferiorly; hinge generally without teeth, or with two very small rudimentary teeth; ligament dorsal, linear, sub-interior, inserted in a long and narrow furrow; two muscular impressions, of which the anterior is very small, with or without longitudinal grooves or furrows.

Mytilus Magellanicus.
M. erosus.
M. crenatus.
M. decussatus.
M. hirsutus.
M. elongatus.
M. latus.
M. zonarius.
M. ungulatus.
M. violaceus.
M. opalus.
M. smaragdinus.
M. corneus.
M. edulis.
M. retusus.
M. Hesperianus.
M. perna.
M. exustus.
M. bilocularis.
M. ovalis.
M. ustulatus.
M. Domingensis.
M. Senegalensis.
M. Afer.
M. achatinus.
M. ungularis.
M. planulatus.
M. borealis.
M. Galloprovincialis.
M. angustanus.
M. lineatus.
M. lacunatus.
M. canalis.
M. incurvatus.
M. abbreviatus.

_M. incurvatus._ The incurvated Mytilus.

Nearly smooth, elongated oval, valves inflated and curved near the ligament; apex acute.

_M. Afer._ The African Mytilus.

More or less compressed and sub-triangular, without grooves; byssus very large and much developed; summit entirely terminal and anterior; smooth and radiated with blue or purple, covered with a dark brown epidermis; inside margin blue, shade decreasing to the centre.

_M. crenatus._ The crenated Mytilus.

Species longitudinally grooved, radiated, or striated.

_M. hirsutus._ The bearded Mytilus.

Species with grooves; covered with a shaggy or bearded epidermis.

2. Modiola. Twenty-three species.

Taken by Lamarck from the Mytilus, as it differs by being more transverse than longitudinal, and the beaks, instead of being terminal, are placed beneath the apex.

Shell smooth, sub-transverse, equivalve, regular, sub-triangular, the posterior side short; summits almost lateral; hinge lateral and linear, without teeth; ligament partly interior, placed in a marginal furrow; one sub-lateral elongated muscular impression in each valve.

Modiola Papuana.
M. tulipa.
M. albicosta.
M. vagina.
M. picta.
M. sulcata.
M. plicatula.
M. semifusca.
M. securis.
M. purpurata.
M. barbata.
M. Guyanensis.
M. Adriatica.
M. pulex.
M. discrepans.
M. discors.
M. trapezina.
M. cinnamomea.
M. silicula.
M. plicata.
M. semen.
M. lithophaga.
M. caudigera.

_M. discors._ The discordant Modiola.

Shell elongated oval, very convex, narrowest at the anterior end; striated at the two extremities; summit oblique; exterior greenish; interior white, with sometimes a pink-tinge, and somewhat pearly; crenulated margin.

_M. Papuana._ The Papuan Modiola. Pl. 12, fig. 6.

Species smooth, more or less triangular; summit near the anterior extremity; byssus obsolete in adults.

_M. sulcata._ The furrowed Modiola.

Species striated longitudinally.

3. Pinna. The Wing Shell. Fifteen species.

This genus is the same as constituted by Linnæus; the shell is marine, generally very brittle and fragile, in form resembling an acute angled triangle; usually covered with longitudinal ribs and elevated transverse striæ; generally horn coloured.

This genus is remarkable for the production of an abundant byssus of a fine brown silky texture, which the Italians frequently fabricate into articles of dress, equal in appearance to the finest silk.

The Pinnæ often grow to a large size; they are sometimes found standing erect in the smooth-water bays, with the base of the shell uppermost, but generally affixed by the byssus to rocks and other sub-marine bodies. The filaments that compose the byssus are so tough and strong that the shells are not easily detached.

Shell fibrous, fragile, regular, equivalve, longitudinal, triangular, base gaping and as if truncated; summit pointed and straight; hinge dorsal, longitudinal, linear, and without teeth; marginal ligament occupying almost the whole of the dorsal edge of the shell; one very broad muscular impression behind a trace of the anterior in the summit.

Pinna rudis.
P. flabellum.
P. seminuda.
P. angustina.
P. nobilis.
P. squamosa.
P. marginata.
P. muricata.
P. pectinata.
P. saccata.
P. varicosa.
P. dolabrata.
P. ingens.
P. vexillum.
P. nigrina.

_P. squamosa._ The scaly Pinna.

Species very close and rounded at the posterior extremity; valves convex, covered with vaulted imbricated scales.

_P. flabellum._ The fan Pinna. Pl. 13, fig. 2.

Species gaping at the posterior extremity, which is as if truncated; valves rather rounded at the upper end, and in the shape of an expanded fan; light fawn colour.

_P. pectinata._ The pectinated Pinna. Pl. 13, fig. 1.

Thin, pellucid; longitudinally ribbed and spinous for half its width, obliquely striated transversely on the other half.

FAMILY XVII.
MALLEACEA. Five genera.

1. Crenatula. Seven species.

There is one peculiar distinction between this genus and the Perna; the hinge of the Crenatula is composed of slightly concave callous crenulations, which receive the ligament; while in the Perna it consists of parallel truncated linear teeth (or, rather, riblike joints), corresponding and opposed to the opposite ones, the ligament being inserted only in their interstices.

Shell thin, very delicate, irregular, valves flattened, foliaceous, sub-rhomboidal, sub-equivalve; hinge longitudinal, dorsal, without teeth; ligament sub-multiple, and inserted in a series of rounded cavities corresponding with the dorsal margin; one sub-central muscular impression.

Crenatula avicularis.
C. modiolaris.
C. nigrina.
C. bicostalis.
C. viridis.
C. mytiloides.
C. phasianoptera.

_C. avicularis._ The avicular Crenatula. Pl. 14, fig. 2.

Answers to the above description.

_C. mytiloides._ The muscle-shaped Crenatula.

Oblong, ovate, oblique; base acute; violet coloured, with obscure radiations.

2. Perna. Ten species.

In speaking of the Crenatula, we gave the characteristic distinction, which regarded it natural and expedient to make the Perna form a different genus.

Shell irregular, very compressed, foliaceous, sub-equivalve, rather variable form, gaping at the anterior part of the lower extremity; summit very small, hinge straight, vertical, without teeth; ligament multiple, and inserted in a series of longitudinal parallel furrows.

Perna ephippium.
P. obliqua.
P. isognomon.
P. avicularis.
P. femoralis.
P. canina.
P. marsupiom.
P. sulcata.
P. vulsella.
P. nucleus.

_P. femoralis._ The femoral Perna. Pl. 14, fig. 1.

Species elongated, and with appendages like ears.

_P. vulsella._ The tweezer Perna.

Species elongated, without earlike appendages, or having very small ones.

_P. ephippium._ The saddle Perna.

Species round, compressed, very pearly in the interior; very slightly, if at all, auricled; margin acute; exterior purplish brown.

3. Malleus. The Hammer. Six species.

A shell of a singular form, resembling a pickaxe, found only in the Indian and Australian Seas; there are two species, the white and the black, both of which, when in fine preservation, are highly esteemed, but the white is more rare and valuable.

Shell sub-nacreous, irregular, rugged, sub-equivalve, inequilateral, generally auricled before and prolonged behind, so as to be in form like a hammer; summit entirely anterior; between them and the inferior auricle, an oblique cut or slope for the passage of the byssus; hinge linear, elongated, without teeth; ligament simple, triangular, inserted in a conical oblique cavity, partly exterior; one rather large sub-central muscular impression.

Malleus albus.
M. vulgaris.
M. normalis.
M. vulsellatus.
M. anatinus.
M. decurtatus.

_M. vulgaris._ The common Malleus. Pl. 14, fig. 4.

Species with two earlike appendages; trilobate, colour blackish brown.

_M. albus._ The white Malleus.

Species trilobate; base of the lateral lobe prolonged, without a sinus; the base and the pit of the ligament not distinct; colour white, with transverse undulations.

_M. vulsellatus._ The tweezer Malleus.

Species slightly auricled.

_M. normalis._ The square Malleus.

Species without earlike appendages.

4. Avicula. Thirteen species.

Remarkable for the form of its shell, which resembles, when partially expanded, a bird flying.

Shell foliaceous or not, thin and very fragile, always pearly, sub-equivalve; form sub-regular, but rather variable; summit anterior; valves oblique, the left one with a little notch, through which the byssus passes; sometimes unequally and obliquely auricled; hinge linear, toothless, or with two small rudimentary teeth; ligament more or less exterior, placed in a narrow groove, sometimes enlarged towards the summit; one very large posterior muscular impression; and one very small anterior.

Avicula macroptera.
A. lotorium.
A. semi-sagitta.
A. heteroptera.
A. falcata.
A. crocea.
A. Tarentina.
A. Atlantica.
A. squamulosa.
A. papilionacea.
A. costellata.
A. physoides.
A. virens.

_A. macroptera._ The rounded Avicula. Pl. 14, fig. 3.

Species oval, oblique, the earlike appendages very developed, especially the superior; one tooth at the hinge.

_A. Atlantica._ The Atlantic Avicula.

Obliquely curved, yellowish fawn colour, with dark reddish-brown stains; interior pearly.

5. Meleagrina. Two species.

The form of the shell is orbicular and equivalve, without the elongated transverse base on the cardinal tooth, and the sloping sides of the opening for the passage of the byssus are perceptible on both valves; these peculiarities distinguish it from the Avicula.

Shell sub-equivalve, rotundate, nearly square, externally squamose; the inferior cardinal margin straight, not caudate anteriorly; a sinus at the posterior base of the valves for the passage of the byssus; the left valve being at this place narrow and channelled; hinge linear, without teeth.

Meleagrina margaritifera.
Meleagrina albina.

_M. margaritifera._ The pearl-bearing Meleagrina, sometimes called the mother-of-pearl oyster.

Species slightly oblique, somewhat square, pearly, very thick, compressed; undulated and transversely striated, with a series of lamellated longitudinal scales; exterior greenish, interior pearly. This shell is celebrated for its irridescent colours, and is valued for the beautiful and costly pearls it produces. These pearls are formed from a deposition of the substance destined to line the shell upon sand or other bodies, casually or purposely introduced within the mantle of the animal; the shell itself is the mother-of-pearl used for inlaying, or making various elegant trinkets.

FAMILY XVIII.
PECTINIDES. Seven genera.

1. Pedum. The Shepherd’s Crook. One species.

The common name was given to this genus from the resemblance to a French shepherd’s crook. The shell is of a regular form; its lower valve, in which is a sinus for the byssus, is turned up at the edges, and the upper valve falls within it.

Shell inequivalve, a little eared; apices unequal, distant, rounded, little evident; hinge without teeth; ligament inserted in an oblique groove, prolonged to the summit, and carried within in a kind of spoonlike cavity.

_P. spondyloideum._ The spondylus-shaped Pedum. Pl. 15, fig. 5.

Ovate, wedge shaped, flat; superior valve with longitudinal striæ; white, granulated, and rough; slightly tinged with purple near the beak.

2. Lima. The File Shell. Six species.

No sinus or notch; the valves, thick and gaping, form a lateral opening; the ears are small, but distinct.

Shell oval, more or less oblique, almost equivalve, with small ears, regularly gaping at the anterior part of the lower edge; summits anterior and distant; hinge longitudinal, without teeth; ligament rounded, almost exterior, inserted in a cavity of each valve; central muscular impression divided into three very distinct parts.

Lima inflata.
L. squamosa.
L. glacialis.
L. annulata.
L. fragilis.
L. linguatula.

_L. squamosa._ The scaly Lima. Pl. 15, fig. 3.

Answers to the above description, with valves ventricose, armed with vaulted scales.

_L. fragilis._ The fragile Lima.

Oblong ovate, very pellucid, delicately white, with longitudinal distinct striæ; lower margin denticulated, closely interlocking when the valves are closed.

3. Pecten. The Scallop. Fifty-nine species.

The shells constituting this genus are found in all seas; they are well known, and many of them are very beautiful.

The form is usually regular; their surface is adorned with elevated divergent ribs, varying in number from five to thirty, proceeding from the beaks and terminating at the margins in a scalloped outline.

Some are equivalve, others have one valve flat and the other convex; the colours of the upper valve are brighter than those of the lower.

There is considerable variation in the size and form of the ears, which in some species are equal or nearly so, but in others are unequal; some are so small as to be nearly indistinct. The ribs are variously diversified with beautiful colours and delicate checker-work; the margins are mostly crenated, and oftentimes beautifully coloured.

These shells were formerly worn by Pilgrims on their hat or coat, as a mark of having been to the holy shrine in Palestine.

Shell free, regular, thin, solid, auricled, equivalve, equilateral; summits contiguous; hinge without teeth; a ligamental membrane through all the length of the hinge, besides a short, thick ligament, almost entirely internal, which fills a triangular cavity under the summits; one sub-central muscular impression.

Pecten maximus.
P. medius.
P. Jacobæus.
P. bifrons.
P. ziczac.
P. Latirentii.
P. rastellum.
P. turgidus.
P. flagellatus.
P. aspersus.
P. flavidulus.
P. plica.
P. pleuronectes.
P. obliteratus.
P. Japonicus.
P. Magellanicus.
P. purpuratus.
P. lineolaris.
P. radula.
P. nodosus.
P. pallium.
P. pes-felis.
P. tigris.
P. imbricatus.
P. histrionicus.
P. sauciatus.
P. opercularis.
P. asperrimus.
P. senatorius.
P. aurantius.
P. florens.
P. varius.
P. sanguineus.
P. sinuosus.
P. ornatus.
P. glaber.
P. sulcatus.
P. virgo.
P. unicolor.
P. griseus.
P. distans.
P. Isabella.
P. lineatus.
P. flabellatus.
P. irradians.
P. flexuosa.
P. dispar.
P. quadriradiatus.
P. Islandicus.
P. inflexus.
P. pellucidus.
P. Tranquebaricus.
P. gibbus.
P. miniaceus.
P. pusio.
P. hybridus.
P. sulphureus.
P. lividus.

_P. glaber._ The glabrous Scallop. Pl. 15, fig. 4.

Species of which the two valves are ribbed and almost equally convex, the right a little less, and having its inferior ear less broad than the left, so as to produce a kind of groove for the passage of the byssus.

_P. Jacobæus._ The scallop of St. James.

Species very inequivalve; the left valve being very flat, the right convex; ears equal.

_P. pleuronectes._ The sole Scallop.

Species equivalve, not closing; surface smooth and ribbed within; one valve perfectly white, the other of a brownish or reddish colour.

4. Plagiostoma. Ten fossil species.

Only known as fossils; probably introduced here by Lamarck to serve as a connecting link for the genera Lima, Pecten, Spondylus, and Podopsis.

Shell rather thick, regular, free, sub-equivalve, sub-auriculated; the two valves almost equally convex, both provided with a distinct summit, recurved in the middle of a level surface, with a great triangular slope in the middle; the cardinal base transverse, straight; hinge without teeth; a conical cardinal pit situated below the beak, partly internal, opening outward, and receiving the ligament.

_P. spinosa._ The thorny Plagiostoma.

Subarcuated, the umbo of one shell higher than that of the other, with longitudinal ribs and remote concentric rings.

5. Plicatula. Five species.

Separated from the Spondylus of Linnæus on account of its distinct structure. The ligament is altogether internal; it is without ears, and the prolonged beak so conspicuous in that genus. The Plicatula has the faculty of affixing itself to another body, so that many are found grouped together in clusters. The valves are strongly plaited within and without, closely interlocking with each other.

Shell solid, adhering, sub-irregular, without ears, inequivalve, pointed at the summit, rounded and plaited behind; hinge with two strong teeth in each valve, with a cavity between them, in which the ligament is internally inserted.

Plicatula ramosa.
P. depressa.
P. cristata.
P. reniformis.
P. Australis.

_P. ramosa._ The branched Plicatula. Pl. 15, fig. 2.

Oblong, trigonal, very thick; strong longitudinal plaits; exterior brown, with a yellow tinge, with reddish arrow-shaped markings; interior white.

6. Spondylus. The thorny Oyster. Twenty-one species.

The valves of this genus greatly resemble those of the common oyster, but have ears, and are covered with long recurved or straight-pointed spines.

The lower valve is much larger than the upper, and has foliaceous laminæ, by which it is attached to the other substances. They are found in all seas of hot countries, but particularly in the Indian; they adhere to rocks, coral, &c., oftentimes in large groups.

The usual colours are red, purple, white, brown, or orange, several of which are sometimes blended in the same shell.

Shell solid, adhering, sub-regular, more or less spined, sub-auriculated, inequivalve; the right or inferior valve fixed, much more excavated than the other, and having behind, at the summit, a triangular face, which enlarges and elongates with age; hinge longitudinal, provided in each valve with two strong teeth entering into corresponding cavities; ligament short, almost medial, partly exterior; one sub-dorsal, muscular impression.

Spondylus gædaropus.
S. Americanus.
S. arachnoides.
S. candidus.
S. multilamellatus.
S. coccineus.
S. crassisquama.
S. spathuliferus.
S. ducalis.
S. longitudinalis.
S. costatus.
S. variegatus.
S. longispineus.
S. regius.
S. avicularis.
S. microlepos.
S. croceus.
S. aurantius.
S. radians.
S. zonalis.
S. violacescens.

_S. gædaropus._ The thorny red Spondylus. Pl. 15, fig. 1.

Upper valve red, under one white, with longitudinal striæ or ribs; rough granulations, and somewhat tongue-shaped; rather short truncated spines.

_S. longispineus._ The long-spined Spondylus.

Thickly spined, longitudinally sulcated and ribbed; alternate spines arcuated and tongue-shaped; valves of a reddish colour; umbones orange.

7. Podopsis. Two fossil species.

Only introduced here to fill up the family and keep up the chain of connexion. It approximates the genus Gryphea.

Shell rather thick, sub-regular, symmetrical, equilateral, inequivalve, adhering by the extremity of the shorter valve; the other terminated by a summit pointed, a little recurved and medial; articulation very angular, by means of two very distant condyles.

FAMILY XIX.
OSTRACEA. Six genera.

1. Gryphæa. One species.

This genus resembles the Ostrea, with which it was formerly classed, but from which it is distinguished by the peculiar character of the lower valve. It is very deep and carinated, with a summit terminating in a long spirally recurved beak, slightly turned to one side; the edge sharp and angular.

It is seldom, if ever, attached to other bodies. Shell more finely lamellated than that of the oyster, free or slightly adherent, sub-equilateral, very inequivalve; the lower valve very concave, with a summit more or less recurved like a hook; the upper valve much smaller, and formed like a lid; hinge without teeth; ligament inserted in an oblong arched cavity; one single muscular impression on each valve.

_G. angulata._ The angulated Gryphæa. Pl. 16, fig. 2.

Oblong ovate, with three long longitudinal carinated ribs below; summit of the inferior valve is subvolute. This is a rare shell.

2. Ostrea. The Oyster. Forty-eight species.

As given by Lamarck, is a natural and well-defined family. It is too well known to require description. It fixes itself to other bodies by the laminæ of the whole surface of one valve, and generally remains immoveable, exhibiting no other signs of life other than that of opening its valves to receive nutriment.

Shell irregular, inequivalve, inequilateral, exterior roughly foliaceous, interior somewhat pearly; the left or inferior valve larger, deeper, and adhesive, its summit prolonging with age in a sort of heel, the right or superior valve smaller, more or less in the form of a lid; hinge without teeth; ligament short, sub-interior, inserted in an oblong cardinal cavity, increasing with the summit; muscular impression single and sub-central.

Ostrea edulis.
O. hippopus.
O. borealis.
O. Adriatica.
O. cochlear.
O. cristata.
O. gallina.
O. numisma.
O. lingua.
O. tulipa.
O. Brisiliana.
O. scabra.
O. rostralis.
O. parasitica.
O. denticulata.
O. spathulata.
O. cornucopiæ.
O. cucullata.
O. doridella.
O. rubella.
O. limacella.
O. ruscuriana.
O. Virginica.
O. Canadensis.
O. excavata.
O. mytiloides.
O. sinuata.
O. trapezina.
O. tuberculata.
O. rufa.
O. margaritacea.
O. gibbosa.
O. Australis.
O. elliptica.
O. haliotidæa.
O. deformis.
O. fucorum.
O. plicatula.
O. glaucina.
O. fusca.
O. turbinata.
O. crista-galli.
O. erucella.
O. folium.
O. labrella.
O. imbricata.
O. hyotis.
O. radiata.

_O. edulis._ The eatable Oyster. Pl. 16, fig. 5.

Species orbicular, and not plaited; rugged, with undulated, imbricated scales; one valve flat and the other convex; variable in size; outside greenish brown, inside pearly white, sometimes with a bluish tinge.

_O. Virginica._ The Virginian Oyster.

Species longitudinal and not plaited.

_O. imbricata._ The imbricated Oyster.

Species orbicular and plaited.

_O. crista-galli._ The Cock’s-comb Oyster.

Species strongly plaited longitudinally.

3. Vulsella. The Tweezers. Six species.

This genus has several characteristics which distinguish it from the Ostrea; they are free; the valves and the apices are nearly equal, with a projecting callosity on each valve, depressed underneath, and obliquely arched for the reception of the ligament.

Shell sub-nacreous, sub-regular, sub-equivalve, inequilateral; upper valve finely granulated, or striated longitudinally from the apex to the margin; summits anterior, distant, recurved below; hinge without teeth; ligament undivided, thick, inserted in a rounded cavity, made in a slightly projecting callosity on each valve; muscular impression sub-central, rather large, and two very small ones entirely anterior.

_V. lingulata._ The tongue-like Vulsella. Pl. 15, fig. 6.

Elongated, depressed, transversely striated; pale yellowish brown, with longitudinal darker stripes.

4. Placuna. The Chinese Window Shell. Three species.

This genus received its common name from the thin, transparent nature of the valves of the shell, particularly of the species _placenta_, which by the ingenious Chinese are often polished and used as a substitute for window-glass.

The hinge of the shells of this genus is so peculiar as to make it perfectly distinct; entirely interior, fastened by a ligament shaped like a V on one of the valves.

Shell free, sub-irregular, very thin, almost entirely transparent, flat, sub-equivalve, sub-equilateral, slightly auricled; hinge entirely internal, formed on the superior less valve by two elongated, unequal, oblique ribs converging at the summit, to the interior side of which a ligament like the letter V is inserted in two equally converging, rather deep cavities of the lower valve, which is more convex; one rather small, sub-central muscular impression.

_P. placenta._ The glassy Placuna. Pl. 16, fig. 3.

Sub-orbicular, flat, white, and transparent; finely striated longitudinally, slightly decussated.

5. Anomia. The Antique Lamp. Six species.

When Linnæus formed this genus and named it Anomia, he probably did so from its having no determinate character. Its common name was given it by the fancied resemblance of some of its species to an antique lamp. Like the oyster, they seldom leave their place; they are always affixed to marine bodies by an osseous operculum, formed by the thick extremity of the animal’s muscle. The lower valve is perforated and smaller, conforming to the shape of the substance to which it is affixed.

Shell adhering, irregular, inequivalve, inequilateral, ostraceous; inferior valve rather more flat than the superior, divided at the summit into two sloping branches, whose approaching together forms a large oval hole, through which protrudes a muscle, the extremity of which becomes ossified and adheres to extraneous bodies; one sub-central muscular impression divided into three.

Anomia ephippium.
A. patellaris.
A. cepa.
A. electrica.
A. pyriformis.
A. fornicata.
A. membranacea.
A. squamula.
A. lens.

_A. ephippium._ The Saddle Anomia. Pl. 16, fig. 1.

Shell sub-orbicular, irregularly wrinkled and waved; upper valve convex, under flat and perforated at the hinge, through which passes the ligament by which it is affixed to other bodies; inside pearly, and of various changing colours, such as green, purple, violet, and yellow.

6. Crania. The Scull. One species.

So called from the appearance caused by three holes or cavities on the surface of the lower valve.

Shell irregular, orbicular, inequivalve; the inferior valve almost flat, and marked on the interior with four muscular impressions, sometimes very deep, and of which the two sub-central are sufficiently connected to form but one; the superior valve like a Patella, more or less convex, with four very distinct muscular impressions, rather distant.

_C. personata._ The masked Crania. Pl. 16, fig. 4.

Orbicular; upper valve gibbous and conical, lower valve flat, with three perforations.

FAMILY XX.
BRACHIOPODA. Three genera.

1. Orbicula. One species.

Greatly resembling a Patella, for which it is often mistaken on account of the lower valve being very thin, flat, and adhering.

Shell sub-orbicular, very compressed, inequilateral, very inequivalve; the inferior valve very thin, adherent, and imperforated; the superior valve like a Patella, with a summit more or less inclined towards the posterior side.

_O. Norwegica._ The Norwegian Orbicula. Pl. 17, fig. 4.

Upper valve in the form of a depressed cone, with a summit produced and pointed.

2. Terebratula. Twelve species.

Taken from the Anomia, and with great propriety, as its characteristic differences are very great; the perforation of the Anomia is always in the smaller valve, which is attached to the larger by a cardinal ligament, while in the Terebratula the perforation is always in the larger valve, which is connected to the smaller by teeth at the hinge. In some the valves are smooth, and in others grooved longitudinally.

Shell thin, equilateral, sub-triangular, inequivalve; one of the valves larger and more convex than the other, prolonged behind by a sort of heel, sometimes recurved, and pierced by a round hole at its extremity; frequently sloped more or less by a cleft of variable form; the opposite valve smaller, more flat, sometimes formed like a lid, having in the interior a system of support variable in form and complication in every true species; hinge limited, prominent, and formed by two articulating surfaces of one valve placed between corresponding projections of the other; a kind of tendinous ligament issuing from the sloping cleft of the shell, by which it is attached to marine bodies.

Terebratula vitrea.
T. dilatata.
T. rotunda.
T. flavescens.
T. dentata.
T. dorsata.
T. pisum.
T. globosa.
T. sanguinea.
T. caput-serpentis.
T. truncata.
T. psittacea.

_T. dorsalis._ The dorsal Terebratula. Pl. 17, fig. 1.

The summit of the large valve pierced with a round hole, very circumscribed; grooved longitudinally; valves as if cut sloping in the middle line.

_T. globosa._ The globose Terebratula.

Species smooth, with the valves rounded at their anterior edge.

_T. caput serpentis._ The Serpent’s-head Terebratula.

Species grooved, with the summit or heel of the large valve deeply hollowed even to the edge of the articulation; the slope rounded; the valves sub-bilobate by the apparent slope of the anterior edge.

3. Lingula. One species.

The valves of this genus are united by means of a tubular, fleshy, or membranous peduncle surrounding the narrow part of them, and of which the base is affixed to marine substances.

Shell covered with epidermis, sub-equivalve, equilateral, depressed, elongated, truncated anteriorly, summit middle and posterior, without trace of ligament, but supported at the extremity of a long fibro-gelatinous peduncle, which attaches it vertically to sub-marine bodies; multiple muscular impression.

_L. anatina._ The Duck’s-bill Lingula. Pl. 17, fig. 2.

Covered with a green, shining epidermis, shaped like a duck’s bill, and having a cylindrical peduncle.

CLASS IV.
MOLLUSCA.
TWENTY-TWO FAMILIES.

FAMILY I.
PTEROPODA. Six genera

Some genera of this family are without a testaceous covering, and are mentioned only for the sake of preserving the family entire.

1. Hyalæa. Venus’s Chariot. Two species.

This genus derives its common name from a fancied resemblance to a miniature triumphal car.