Chapter IV: Introduction (2)

_Animal._ Soft, inarticulated, always fixed in a bivalve shell, without head or eyes, having the mouth naked, concealed, and without any hard parts; a large mantle enveloping the whole of the body, forming two laminiform lobes; the edges detached or sometimes united in front. Gills or respiratory organs external, situated on each side between the body and the mantle; circulation simple, the heart with one ventricle; some few ganglions of the different nerves, but no knotted medullary cord.

_Shell._ Always bivalve, enveloping the animal entirely or partially, sometimes free, sometimes affixed; the valves most frequently united on one side by a hinge or ligament. Sometimes attached to the shell are testaceous accessory pieces. Twenty families.

FAMILY I.

TUBICOLA. Six Genera.

1. Genus _Aspergillum_. Pl. V.

_Animal._ Entirely unknown.

_Shell._ Oval, somewhat elongated, striated longitudinally, conic, club-shaped, having two valves incrusted on one side of the club, open at its attenuated extremity, and terminated at the other by a convex disk, pierced by a number of small perforations, and encircled by a dilated margin of papyraceous tubes, resembling a plaited ruff—smaller extremity always open. This is a well known, but rare shell, found in sandy places in low water in the Indian ocean. Four species.

Aspergillum Javanum. A. vaginiferum. A. Novæ Zælandiæ. A. agglutinans.

2. Genus _Clavagella_. Pl. VI.

_Animal._ Unknown.

_Shell._ A tubular sheath, testaceous, attenuated, and open before; terminating posteriorly in an oval, sub-compressed club, roughened by spiniform tubes—one valve fixed in the side of the club, the other free in the tube. Inhabits the Indian seas. Four species.

Clavagella aperta. C. cristata. C. tibialis. C. Brocchii.

3. Genus _Fistulana_. Pl. VI.

_Animal._ Provided with two protuberant calcareous tubes, covering parts of its body at the open end of the tube, each of which is terminated with from five to eight cup-shaped calcareous or corneous appendages. It inhabits the sand, and perforates wood, stones, and sometimes shells.

_Shell._ Lamarck asserts that the tube and shell of this genus are quite distinct. They have the shell free and detached within the sheath, and neither of the valves fixed into the partition of the tube, which is most generally testaceous, closed, and retort-shaped at the posterior extremity. Inhabits the Indian seas. Four species.

Fistulana clava. F. corniformis. F. gregata. F. lagenula.

4. Genus _Septaria_. Pl. VI.

_Animal._ Unknown.

_Shell._ A very long testaceous tube, gradually attenuated to its upper end, and divided internally by vaulted divisions seldom complete, the extremity of which is terminated by two slender tubes without interior partitions. Specimens of this genus have been found five feet long. Found in sand on the shores of the Indian seas. Two species.

Septaria arenaria. S. maculata.

5. Genus _Teredina_. Pl. VI.

A fossil genus; consisting of a testaceous cylindrical sheath, the posterior extremity closed, and exhibiting the two valves of the shell it encloses; the anterior end open. Two fossil species.

6. Genus _Teredo_. Pl. VI.

_Animal._ Body very much elongated, vermiform: mantle very fine, tubular, opening only at front and below for the issue of a teat-shaped foot; mouth small; very short, distinct tubes; the inferior or respiratory one somewhat larger than the superior; labial appendages short and striated; branchiæ very long, narrow, united, and prolonged throughout the extent of the tubular cavity of the mantle; only one large contractile muscle between the valves; at the point of junction of the mantle and tubes is a muscular ring, in which is implanted a pair of corneo-calcareous appendages.

_Shell._ Thick, solid, very short or annular, open before and behind; valves equal, equilateral, angular and trenchant before, only touching each other by the opposite edges; no hinge; a considerable spoon-like cavity; only one feeble muscular impression. Tube more or less distinct from the substance in which the animal lives, cylindrical, straight or winding, and closing with age at the buccal extremity so as to envelope the animal and its shell; at the other end it is always open, and divided internally into two syphons by a partition in the middle. Inhabits the European seas in timber. Three species.

Teredo navalis. T. palmulata. T. gigantea.

FAMILY II.

PHOLADARIA. Two Genera.

1. Genus _Pholas_. Pl. VI.

_Animal._ Without a tubular sheath, projecting anteriorly into two united tubes, frequently surrounded by a common skin, and the posterior extremity provided with a short muscular foot, flattened at its extremity.

_Shell._ Multivalve, equivalve, transverse, gaping at both ends, with various accessory pieces either on the hinge or below it. Inhabits the Indian seas and American shores. Eighteen species.

Pholas dactyla. P. orientalis. P. candida. P. dactiloides. P. papyracea. P. tuberculata. P. silicula. P. callosa.

· · · · ·

P. costata.* P. clavata.* P. ovum.* P. lancellata.* P. crispata.* P. truncata.* P. californica.* P. penita.* P. oblongata.* P. cuneiformis.*

2. Genus _Gastrochæna_. Pl. VI.

_Animal._ Unknown.

Always without accessory pieces, therefore easily distinguished from the Pholas.

_Shell._ Equivalve, somewhat cuneiform with a very large oval and oblique aperture anteriorly; posterior extremity nearly closed; hinge linear; marginal and without teeth. Three species.

Gastrochæna cuneiformis. G. mytiloides. G. modiolina.

FAMILY III.

SOLENEA. Four genera.

1. Genus _Solen_. Pl. VI.

_Animal._ Body cylindroid, much elongated; the mantle in form of a canal open at both ends, closed in the rest of its extent by a thick epidermis which surrounds it; a cylindroid anterior foot.

_Shell._ Equivalve, extremely inequilateral, the summits very small, and entirely at the commencement of the dorsal line; one or two teeth in the hinge. Inhabits the seas of America and Europe. Twenty-one species.

Solen vaginus. S. corneus. S. pygmæus. S. ambiguus. S. Dombeii. S. Javanicus. S. Caribæus. S. violaceus. S. antiquatus. S. vaginoides. S. siliqua. S. cultellus. S. planus. S. constrictus. S. coarctatus.

· · · · ·

S. ensis.* S. minutus.* S. viridis.* S. centralis.* S. rostratus.* S. giganteus.*

2. Genus _Panopæa_. Pl. VI.

_Animal._ Unknown.

The situation of the ligament, and the prominency of the apex, are the characters which distinguish it from the Mya.

_Shell._ Regular oval, elongated, gaping at both ends, equivalve, inequilateral; summit little marked and anterodorsal; hinge complete; similen formed by a conical primary tooth, before a short, compressed, ascending callosity, ligament exterior, attached to the callosity; two muscular impressions. Inhabits the Mediterranean Sea. One species.

Panopæa Aldrovandi.

3. Genus _Solecurtus_. Pl. VI.

_Animal._ Unknown.

_Shell._ Oval, elongated, equivalve, subequilateral, with edges nearly straight and parallel, the extremities equally rounded, and, as it were, truncated; summits but little marked; hinge without teeth, or formed by some rudimentary primary teeth, ligament projecting, affixed to thickened callosities; two distinct rounded muscular impressions.—Mediterranean Sea and coasts of America. Ten species.

Solecurtus radiatus. S. strigilatus. S. legumen.

· · · · ·

S. fragilis.* S. costatus.* S. Caribæus.* S. lucidus.* S. Nuttallii.* S. subteres.* S. Californianus.*

4. Genus _Glycimeris_. Pl. VI.

_Animal._ Unknown.

The few species of this genus yet known have been blended, by previous authors, either with the Mya or Solen, but from either they are easily distinguished.

_Shell._ Covered with epidermis, slightly irregular, elongated, gaping at both ends, equivalve, exceedingly inequilateral; summits little marked; hinge toothless; a longitudinal callosity. Ligament exterior, affixed to very projecting callosities on the shortest side of the shell; two distinct muscular impressions. Inhabits the North seas. Two species.

Glycimeris margaritacea. G. siliqua.

FAMILY IV.

MYARIA. Two genera.

1. Genus _Mya_. Pl. VI.

_Animal._ Subcylindrical, enveloped in a mantle pierced only with one interior and inferior hole for the passage of a very small and conical foot; the tubes very considerable, and completely united; a tolerably large mouth, oval, and with simple lips; very small labial appendages: branchial laminæ inconsiderable; the external very short, the internal united with that of the opposite side.

_Shell._ Surrounded with a thick epidermis, which is prolonged upon the tubes and the edges of the mantle of the animal; tolerably solid, with fine trenchant edges; the summits very little marked; hinge dissimilar; one or two oblique cardinal folds, divergent, behind a horizontal spoon-shaped hollow upon the left valve, corresponding with a hollow; horizontal and cardinal in the right valve; two distinct muscular impressions. Inhabits the British and American coasts. Eight species.

Mya truncata. M. arenaria. M. erodona. M. solenimyalis.

· · · · ·

M. hyalina.* M. cancellata.* M. acuta.* M. mercenaria.*

2. Genus _Anatina_. Pl. VI.

_Animal._ Unknown.

_Shell._ Transverse, subequivalve, gaping at both valves, or in one only; no cardinal teeth; one broad primary tooth in both valves, projecting interiorly; a lateral plate running obliquely under the primary teeth. Sometimes there is a fissure extending from the apex, giving the appearance of a second plate or rib. Inhabits the British and American seas. Twelve species.

Anatina laterna. A. truncata. A. subrostrata. A. trapezoides. A. rugosa. A. imperfecta. A. longirostris. A. globulosa. A. myalis. A. rupicola.

· · · · ·

A. Leana.* A. papyracea.*

FAMILY V.

MACTRACEA. Seven genera.

1. Genus _Lutraria_. Pl. VI.

_Animal._ Body oval, much compressed, or subcylindrical; the mantle enclosed only in the half of its inferior side: foot small and projecting but little beyond the abdominal mass, tubes long, distinct or united. This genus is perfectly distinct from the Mactra, to which it formerly belonged, on account of its having no lateral teeth. It is called by De Blainville, Lutricola, from its being found very deep in mud or sand at the mouth of rivers.

_Shell._ Oval or elongated, regular, equivalve, more or less inequilateral, sometimes but slightly gaping: edges always simple and trenchant; summits feebly marked; hinge subsimilar, formed by two very small divergent cardinal teeth; two very distinct muscular impressions united by a palleal impression profoundly sineous to the rear. Inhabits the seas of Europe and America. Fourteen species.

Lutraria solenoides. L. rugosa. L. compressa. L. piperata. L. tellinoides. L. candida. L. elliptica. L. papyracea. L. plicatella. L. crassiplica. L. complanata.

· · · · ·

L. lineata.* L. Nuttallii.* L. caniculata.*

2. Genus _Mactra_. Pl. VI.

_Animal._ Body oval and pretty thick; edges of the mantle thick, smooth, or without tentacular papillæ, augmented behind by two indistinct tubes; mouth small and oval; labial appendages narrow; branchial laminæ very small, and united in their length among themselves and with those of the opposite side; foot oval, trenchant, very long.

_Shell._ The Mactra has a peculiar hinge distinguishing it from all other genera. It is triangular, with a curved or angular compressed tooth on each valve, with a small oblique cavity on each side, to which is attached the ligament. Two lateral teeth, one near the primary tooth and one near the ligament. The shape of the shell is subtriangular or oblong; exterior smooth, striated, or ribbed transversely; two muscular impressions united by a narrow marginal tongue. Inhabits the British and American coasts. Forty-four species.

Mactra spengleri. M. striatella. M. carinata. M. straminea. M. Australis. M. violacea. M. fasciata. M. turgida. M. plicataria M. rufescens. M. maculata. M. subplicata. M. triangularis. M. lactea. M. abbreviata. M. crassatella. M. helvacea. M. grandis. M. stultorum. M. maculosa. M. ovalina. M. castanea. M. rufa. M. squalida. M. brasiliana. M. donacina. M. depressa. M. lilacea. M. trigonella. M. deltoides. M. alata.

· · · · ·

M. gigantea.* M. solida.* M. oblonga.* M. californica.* M. arctata.* M. nucleus.* M. alba.* M. similis.* M. fragilis.* M. lateralis.* M. deaurata.* M. planulata.* M. tellinoides.*

3. Genus _Crassatella_. Pl. VI.

_Animal._ Unknown.

_Shell._ Close, suborbicular or transverse, striated longitudinally, denticulated, regular, equivalve, inequilateral, summits well marked, and turned to the front: primary teeth somewhat divergent with a hollow at the side; no lateral teeth nor obsolete ones; ligament internal and inserted into a pit in the hinge. It is easily known from the Mactra and Lutraria by the valves fitting exactly. The living species of this genus only exist in the seas of Australasia, while in a fossil state we find at least seven species in France. Eleven species.

Crassatella kingicola. C. donacina. C. sulcata. C. rostrata. C. glabrata. C. subradiata. C. contraria. C. cuneata. C. Erycinæa. C. cycladea. C. striata.

4. Genus _Erycina_. Pl. VI.

_Animal._ Unknown.

_Shell._ Somewhat longer than high, subtrigonal, regular equivalved, inequilateral, gaping but little or not at all; summits well marked and a little inclined to the front; hinge subsimilar; two unequal cardinal teeth converging to the summit; two oblong, compressed, short, and inserted lateral teeth; ligament internal and situated in a pit. Owing to the equivocal character of this genus it is somewhat difficult to judge of the hinge. Inhabits the Indian and American seas. Two species.

Erycina cardioides. E. striata.

5. Genus _Ungulina_. Pl. VI.

_Animal._ Unknown.

_Shell._ Vertical or sublongitudinal, a little irregular, not gaping, equivalve, subequilateral, with summits a little marked; hinge dorsal, formed by a cardinal tooth; two long muscular impressions, one short primary cleft tooth in each valve, with an oblong groove divided in the middle of the margin, ligament internal inserted in a pit. Two species.

Ungulina oblonga. U. transversa.

6. Genus _Solemya_. Pl. VI.

_Animal._ Unknown.

_Shell._ Covered with a thick epidermis, enclosing it entirely except at the extremities, regular, somewhat thick, oval, elongated, straight and parallel edges, also rounded at its two extremities, valves equal, very inequilateral; the anterior side much longer than the posterior; summits feebly marked; hinge subsimilar, formed by a cardinal tooth, dilated, compressed, and a little reflexed above; subexterior ligament inserted upon the tooth, and nearly at the posterior extremity of the shell; two small, rounded, widely separated muscular impressions, without any visible abdominal impression. Four species.

Solemya Australis. S. Mediterranea.

· · · · ·

S. velum.* S. borealis.*

7. Genus _Amphidesma_. Pl. VI.

_Animal._ Very imperfectly known.

_Shell._ Transverse, inequilateral, somewhat rounded or suboval; sides slightly gaping; hinge with one or two cardinal teeth, and a narrow groove for the internal ligament; ligament double, the external one short, the internal one fixed in the internal grooves. The two ligaments distinguish this genus from all other bivalves. Inhabits the West Indian and American seas. Forty-five species.

Amphidesma variegatum. A. donacillum. A. lacteum. A. corneum. A. albellum. A. flexuosum. A. prismaticum. A. phaseolinum. A. Tenuii. A. purpurescens. A. nucleolum. A. physioides. A. pulchrum. A. pallidum. A. formosum. A. roseum. A. corbuloides. A. glabrellum. A. lucinale. A. Boysii. A. lenticulare. A. cancellatum. A. reticulatum. A. duplicatum. A. læve. A. prismaticum. A. ellipticum. A. subtruncatum. A. solidum. A. cordiforme. A. rupium. A. lamellosum. A. crenulatum. A. punctatum. A. multicostatum. A. siculum.

· · · · ·

A. transversum.* A. rubro-lineata.* A. decisa.* A. bellastriata.* A. orbiculata.* A. equalis.* A. punctata.* A. radiata.* A. lepida.*

FAMILY VI.

CORBULACEA. Two genera.

1. Genus _Corbula_. Pl. VI.

_Animal._ Unknown.

_Shell._ Tolerably solid, regular, inequivalve, inequilateral with a conical, flexed, ascending, primary tooth in each valve; a cavity at the side; no lateral teeth; ligament interior, placed in the cavities; two neighbouring muscular impressions. Inhabits the British and American seas. Ten species. Four fossil.

Corbula Australis. C. sulcata. C. erythrodon. C. ovalina. C. semen. C. Taitensis. C. nucleus. C. impressa. C. porcina.

· · · · ·

C. contracta.*

2. Genus _Pandora_. Pl. VI.

_Animal._ Body much compressed, somewhat elongated, in form of a furrow, in consequence of the union of the edges of the mantle, and its continuation with the tubes, which are united and short; foot small, thickest in front, and issuing through a tolerably large cleft in the mantle.

_Shell._ Regular, white, elongated, much compressed, inequivalved, inequilateral; right or upper valve quite flat, with a fold; summits feebly marked; hinge anomalous, formed by a transverse cardinal tooth on the right; valve entering a corresponding cavity in the left; ligament internal, oblique, triangular, inserted in a somewhat deep pit, with edges a little projecting on each valve; two round muscular impressions. Inhabits the Mediterranean, British, and American seas. Four living species, and two fossils, according to Defrance.

Pandora rostrata. P. obtusa.

· · · · ·

P. trilineata.* P. punctata.*

FAMILY VII.

LITHOPHAGA. Three genera.

1. Genus _Saxicava_. Pl. VI.

_Animal._ Long, subcylindrical, the mantle closed in all parts, prolonged behind by two long tubes, thick and close together externally, pierced interiorly and in front with a round orifice, for the passage of a very small foot; mouth very large; labial appendages small; branchial laminæ free, the external pair much shorter than the internal.

Lamarck has thought proper to remove this genus from the Mytilus; it possesses the faculty, like the Pholas, of penetrating rocks and substances, and cannot be extracted but by breaking the substance in which it is imbedded.

_Shell._ Thick, with an epidermis, a little irregular, elongated, subcylindrical, obtuse at both ends; summits feebly marked; hinge toothless, or with a very small rudimentary tooth; ligament external, somewhat inflated; two round muscular impressions distinct, and several others irregular. Inhabits the British and American seas, in cavities, which they bore in rocks or wood. Nine species.

Saxicava rugosa. S. gallicana. S. veneriformis. S. pholadis. S. Australis.

· · · · ·

S. distorta.* S. rhomboides.* S. carditoides.* S. californica.*

2. Genus _Petricola_. Pl. VII.

_Animal._ Unknown.

_Shell._ Subtrigonal, more or less irregular, transverse, inequilateral; upper side narrowed and a little gaping; lower side rounded; hinge with two teeth in each valve, or in one valve only. Inhabits the Australian seas, boring into wood and rocks. Thirteen species.

Petricola lamellosa. P. Ochrolenca. P. Semilamellata. P. lucinalis. P. striata. P. costellata. P. recellaria. P. exilis. P. ruperella. P. chamoides. P. pholadiformis. P. labagella. P. linguatula.

3. Genus _Venerirupis_. Pl. VII.

_Animal._ Unknown, but probably resembling the Venus.

Another lithophagous shell, taken from the genus Venus, and distinguished from it by the different disposition of the teeth.

_Shell._ Transverse, inequilateral, posterior side short, the anterior gaping slightly. Hinge with two teeth on the right valve, three on the left, and sometimes three on both—these are small, near together, and parallel. Ligament exterior. Inhabits the British seas, boring into rocks and clay. Eight species.

Venerirupis perforans. V. nuclea. V. Ira. V. corditoides. V. exotica. V. distans. V. crenata. V. alata.

FAMILY VIII.

NYMPHACEA. Ten Genera.

This family is divided into N. Solenaria and N. Tellinaria, from their resemblance to the Solen and Tellina.

N. SOLENARIA. Three genera.

1. Genus _Sanguinolaria_. Pl. VII.

_Animal._ Unknown.

_Shell._ Oval, compressed, a little elongated, gaping but little, equivalve, subequilateral, rounded at both extremities; no mark of posterior keel; summits feebly marked; hinge formed by one or two contiguous cardinal teeth upon each valve; ligament projecting, two round muscular impressions, distant and joined by a narrow palleal impression strongly sinuous behind. Inhabits the sea at Jamaica and shores of America. Nine species.

Sanguinolaria occidens. S. rosea. S. alba. S. livida. S. rugosa.

· · · · ·

S. fusca.* S. lusoria.* S. Nuttallii.* S. Californiana.*

2. Genus _Psammobia_. Pl. VII.

_Animal._ Unknown.

Resembling the Tellina, from which it was taken, but not having an irregular plait on the anterior part.

_Shell._ Transverse, oblong-ovate, or elliptical, flattened, slightly gaping at one side; summits projecting; hinge formed by two primary teeth in the left valve, and one in the opposite one Inhabits the European and American seas. Twenty-one species.

Psammobia virgata. P. ferroensis. P. vespertina. P. muculosa. P. alba. P. Cayennensis. P. lævigata. P. Tellinella. P. cærulescens. P. elongata. P. flavicans. P. squamosa. P. pulchella. P. aurantia. P. fragilis. P. livida. P. galathea.

· · · · ·

P. lusoria.* P. fusca.* P. Pacifica.* P. Florida.*

3. Genus _Psammotæa_. Pl. VII.

_Animal._ Unknown.

_Shell._ Of the same form as the Psammobia, but differing in the number of teeth, the left valve of the Psammotæa having only one tooth; and sometimes one valve is without teeth, while the other has two; ligament exterior, attached to callosities at the hinge, and without an irregular plait. Inhabits the Australian seas. Seven species. One fossil species.

Psammotæa violacea. P. zonalis. P. pellucida. P. candida. P. tarentina. P. donacina. P. serotina.

N. TELLINARIA. Seven Genera.

The two last of these genera have no lateral teeth, the rest have one or two.

4. Genus _Tellina_. Pl. VII.

_Animal._ Body triangular, much compressed: the free edge of the mantle furnished with a row of tentacular, largest and longest in the rear; foot very large, compressed and pointed to the front; buccal appendages nearly as large as the bronchial laminæ, of which the external pair are much smaller than the internal; the anterior contractile muscle larger than the other; tubes very distinct.

_Shell._ Of a somewhat variable form, generally striated longitudinally and much compressed, equivalved, more or less inequilateral; the anterior side almost always longer and more rounded than the posterior, which constantly presents a flexuous fold, at least at its inferior edge; summits feebly marked; hinge similar; one or two cardinal teeth; two lateral teeth, far apart with a pit at their base in each valve; ligament posterior, large; round muscular impressions. The finest species of this beautiful shell are found in the pearl fisheries of Ceylon; and numerous species on the American shore. Sixty-eight species.

Tellina unimaculata. T. virgata. T. semizonalis. T. staurella. T. lutirostra. T. rostrata. T. Spengleri. T. radiata. T. crucigera. T. elliptica. T. albinella. T. rosea. T. foliacea. T. operculata. T. chloraleuca. T. remies. T. sulcata. T. crassa. T. exilis. T. donacina. T. nitida. T. striatula. T. decussata. T. obliqua. T. nymphalis. T. capsoides. T. seradiata. T. margaritina. T. strigosa. T. planata. T. depressa. T. pulchella. T. fabula. T. tenuis. T. sulphurea. T. cornuta. T. iris. T. levigata. T. linguafelis. T. rugosa. T. lacunosa. T. gargadia. T. pristis. T. gigas. T. scalaris. T. psammotella. T. scobinata. T. Brasiliana. T. umbonella. T. deltoidalis. T. multangula. T. solidula. T. polygona.

· · · · ·

T. ostracea.* T. intastriata.* T. polita.* T. tenera.* T. flexuosa.* T. secta.* T. decorate.* T. lateralis.* T. alternata.* T. vimaculata.* T. pumicea.* T. alta.* T. nasuta.* T. lineata.* T. sordida.*

5. Genus _Tellinides_. Pl. VII.

_Animal._ As above.

This genus is very nearly allied to the Psammobia, Tellina, and Lucina, but upon close examination it will be found to be distinct from either.

_Shell._ Equilateral, transverse, somewhat elongated, nearly without the flexuous plait; two divergent cardinal teeth, of which the anterior is but little distant from the summit. Inhabits the Bay of Naples. Two species. One species is found on the shores of America.

Tellinides Timorensis.

· · · · ·

T. rosea.*

6. Genus _Corbis_. Pl. VII.

_Animal._ Differing slightly from the Lucina.

This genus was classed by Lamarck with the Lucina, but the great difference in the organization of the animals discovered by Cuvier, has made this a distinct genus.

_Shell._ Equivalve, transverse, without any irregular fold on the anterior margin, having the beaks flexed inward and opposite; two cardinal teeth; two lateral, the posterior of which is nearest the hinge; muscular impressions simple, ligament external. Inhabits the Indian Ocean.

Corbis fimbriata. C. maculata.

7. Genus _Lucina_. Pl. VII.

_Animal._ Very imperfectly known.

_Shell._ Inequilateral, suborbicular, beaks small, pointed, and oblique; two divergent cardinal teeth, one of which is bifid, and which vary or disappear with age; two lateral teeth sometimes obsolete, the posterior approaches nearest to the cardinal teeth; two muscular impressions far apart, the posterior in shape of a band, sometimes very long; ligament external. Inhabits the British and American seas. Twenty-six species.

Lucina Jamaicensis. L. edentula. L. radula. L. lactea. L. circinaria. L. columbella. L. mutabilis. L. squamosa. L. Peruviana. L. fimbriata. L. undata. L. divaricata. L. scabra. L. sinuata. L. lutea. L. globularis. L. digitalis. L. Pecten. L. reticulata. L. carmaria. L. concentrica.

· · · · ·

L. bella.* L. Pennsylvania.* L. sphæroides.* L. Californica.* L. Nuttallii.*

8. Genus _Donax_. Pl. VII.

_Animal._ As in Tellina.

_Shell._ Transverse, inequilateral, equivalve; anterior side short and obtuse; two primary teeth in one or both valves; one or two lateral teeth varying in distance; two round muscular impressions; ligament, external, short, and inserted at the posterior impression. Inhabits the seas of Europe and America. Thirty-one species.

Donax pubescens. D. cuneata. D. radians. D. abbreviata. D. ringens. D. Cayennensis. D. denticulata. D. cinatina. D. cardioides. D. scorta. D. compressa. D. columbella. D. Australis. D. bicolor. D. merois. D. scripta. D. trunculata. D. fiabagella. D. Martiniænsis. D. triquetra. D. rugosa. D. elongata. D. deltoides. D. veneriformis. D. Vittata. D. granosa. D. epidermia. D. minima.

· · · · ·

D. variabilis.* D. fossar.* D. Californica.*

9. Genus _Capsa_. Pl. VII.

_Animal._ As above.

_Shell._ Transverse, equivalve, valves approximate and close; three primary teeth in the right valve, and a single bifid tooth in the left, inserted into a cavity in the opposite one; no lateral teeth; ligament external and on the short side, as in Donax, from which it was separated by Lamarck, on account of the peculiarity of the hinge, inhabits the Indian Ocean. Three species.

Capsa levigata. C. Braziliensis. C. Donaoides.

10. Genus _Crassina_. Pl. VII.

_Animal._ As above.

_Shell._ Distinguished from the Venus by having only two teeth on each valve, and from the crasatella by the position of the ligament; solid, suborbicular, thick, hinge with two strong diverging primary teeth in the right valve, and two unequal ones on the other; ligament external. Inhabits the Scottish and Devonshire coasts. One species.

Crassina Danmoniensis.

FAMILY IX.

CONCHACEA. Seven Genera.

This family is divided into _Conchæ Marinæ_, and _Conchæ Fluviatiles_.

CONCHÆ MARINÆ. Four Genera.

1. _Cyprina._ Pl. VII.

_Animal._ Thick, oval, foot compressed, falciform, geniculated mantle closed behind, and pierced by two oval apertures with cirrous edges: no veritable tubes.

_Shell._ With epidermis; thick, regular, substriated longitudinally, sub-cordiform, equivalved, inequilateral; summits strongly flexed to the front and often contiguous; hinge thick, subsimilar, formed by three slightly converging cardinal teeth, and by a posterior lateral tooth, sometimes obsolete; ligament very thick; muscular impressions distant, subcircular, and united by a narrow marginal band. Inhabits the Atlantic Ocean and British seas. Two living species. Seven fossil.

Cyprina tennistria. C. Icelandica.

2. Genus _Cytherea_. Pl. VII.

_Animal._ Oval or round, generally but little compressed; edges of the mantle undulous, and garnished with tentacular cirri in one row; foot considerable, compressed, trenchant, in other respects diversiform; tubes tolerably elongated, and most usually united; mouth small; labial appendages quite small; branchiæ wide, short, free, or not united either with one another or with those of the opposite side.

_Shell._ Solid, equivalve, regular, inequilateral; summits equal, reflexed, and slightly projecting; four primary teeth on one valve, of which three are divergent, and approximating at the base, and one remote—this circumstance easily distinguishing it from the Venus. On the other valve are three primary divergent teeth with a distant cavity parallel with the edge. Inhabits the British, Mediterranean, and American seas. Eighty-three living species. Nine fossil.

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

· · · · ·

C. occulta.* C. callosa.* C. crassatelloides.*

3. Genus _Venus_. Pl. VII.

_Animal._ As above.

_Shell._ Solid, thick, regular, perfectly equivalved and close, more or less inequilateral; summits well marked and inclined to the front; hinge subsimilar; the middle cardinal tooth forked, or three cardinal teeth more or less contiguous and convergent towards the summits; ligament thick, often arcuated, convex, exterior; two distant muscular impressions; cordiform depressions beneath the beaks. Inhabits the British and American seas. One hundred living species. Nine fossil.

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

· · · · ·

V. notata.* V. præparea.* V. elevata.* V. inequalis.* V. castanea.* V. Nuttallii* V. staminea.* V. Californica.* V. lamellifera.* V. Mortoni.*

4. Genus _Venericardia_. Pl. VII.

_Animal._ Nearly as above.

_Shell._ Suborbicular, inequilateral, equivalve, sides having usually longitudinally rayed ribs; hinge with two oblique cardinal teeth in each valve, turned in the same direction. Five living species. Ten fossil species.

Venericardia Australis. V. imbricata. V. flammea. V. Tankervillii. V. crassicosta.

CONCHÆ FLUVIATILES. Three Genera.

5. Genus _Cyclas_. Pl. VII.

_Animal._ Body oval, thick; edges of the mantle simple; tubes short and united; foot wide, compressed at base, and terminated by a sort of leg or appendage.

The shells of this genus are very small, found buried in the mud of fresh waters; summits never eroded, but some species are so thin as to be transparent.

_Shell._ With an epidermis, oval, or suborbicular, regular, equivalved, inequilateral; summits obtuse, contiguous or turned anteriorly; hinge similar, complex, formed by a slightly variable number of cardinal teeth, and by two separated lateral teeth with a pit at the base; ligament exterior, posterior, and inflated; two distant muscular impressions, united by a faintly marked abdominal band, and without posterior excavation. Fifteen species.

Cyclas cornea. C. obliqua. C. obtusalis. C. Australis. C. striatina. C. rivicola. C. lacustris. C. calyculata. C. fontinalis. C. sulcata.

· · · · ·

C. Sarratogea.* C. Rhomboidea.* C. similis.* C. Partumeia.* C. dubia.*

6. Genus _Cyrena_. Pl. VII.

_Animal._ As above.

_Shell._ Rounded and trigonal, ventricose, inequilateral; hinge with three teeth on each valve; two lateral teeth, one of which is near the primary ones; ligament exterior, situated on the largest side. The apices are always eroded or carious in shells of this genus. Inhabits the rivers of China. One is found on the coast of Carolina. Ten living species. One fossil.

Cyrena orientalis. C. depressa. C. fuscata. C. violacea. C. Ceylonica. C. trigonella. C. cor. C. fluminea. C. Bengalensis.

· · · · ·

C. Caroliniensis.*

7. Genus _Galathea_. Pl. VII.

_Animal._ As above.

_Shell._ Equivalve, subtrigonal, covered with a greenish epidermis; the surface beneath is white, with several violet streaks radiating from the summit to the margin; two furrowed cardinal teeth upon one valve, three upon the other, the middle one being largest and callous; muscular impressions double and lateral. Inhabits the rivers of Ceylon. One species.

Galathea radiata.

FAMILY X.

CARDIACEA. Five Genera.

1. Genus _Cardium_. Pl. VII.

_Animal._ Body somewhat inflated; mantle edged with tentacular cirri in all its inferior part; tubes united, of moderate size, and provided with cirri at the extremity; mouth transverse, very wide, with moderate labial appendages; foot very large, cylindrical, somewhat inclined anteriorly; branchiæ thick, rather small, especially the external laminæ: the internal united in all their extent.

_Shell._ Inflated, equivalve, sub-cordiform (when viewed anteriorly, usually costated from the apex to the circumference); summits very evident, but slightly flexed to the front; hinge complex, similar, formed of two oblique, conical cardinal teeth, and of two distant lateral teeth, upon each valve; ligament dorsal, posterior and very short. Inhabits the European and American seas. Fifty-seven living species. Fourteen fossil.

Cardium indicum. C. Asiaticum. C. fimbriatum. C. aculeatum. C. tuberculatum. C. apertum. C. bullatum. C. echinatum. C. biradiatum. C. pectinatum. C. isocardium. C. angulatum. C. serratum. C. costatum. C. ringens. C. tennicostatum. C. psudolima. C. crinaceum. C. Basilianum. C. papyraceum. C. ciliare. C. levigatum. C. eolicum. C. elongatum. C. rugosum. C. unedo. C. medinum. C. tumotiferum. C. retusum. C. rusticum. C. Greendlandicum. C. crenulatum. C. minotum. C. scobinatum. C. cardissum. C. inversum. C. ventricosum. C. obtusum. C. fragum. C. lineatum. C. edule. C. latum. C. exigunum. C. rosenum. C. hemicardium. C. Junoniæ. C. muricatum. C. marmoreum. C. sulcatum. C. cifidium.

· · · · ·

C. Mortonii.* C. substriatum.* C. Nuttallii.* C. Californianum.* C. quadragenarium.* C. Pennulatum.* C. pubescens.*

2. Genus _Cardita_. Pl. VII.

_Animal._ Body suborbicular, terminated superiorly by a sort of hook; mantle but little open; foot terminated at its extremity by a part much narrower than the base; superior lobes of the branchiæ very short.

_Shell._ Thick, solid, equivalve, more or less inequilateral; summit dorsal always much flexed anteriorly; hinge similar, formed by two oblique teeth, one short, cardinal or apicial, the other postapicial, long, lamellous and arcuated; ligament elongated, subexterior and inserted; two very distinct muscular impressions, united by a palleal band, narrow and semicircular. Inhabits the Mediterranean and American seas. Twenty-three living species. Four fossil.

Cardita Ajar. C. squamosa. C. crassicosta. C. calyculata. C. nodulosa. C. trapezia. C. sulcata. C. turgida. C. phrenetica. C. rufescens. C. subaspera. C. intermedia. C. depressa. C. sinuata. C. citrina. C. orbularis. C. bicolor. C. concamerata. C. aviculina. C. sublevigata. C. lithophagella.

· · · · ·

C. borealis.* C. incrassata.*

3. Genus _Cypricardia_. Pl. VII.

_Animal._ As above.

_Shell._ Obliquely elongated, equivalve, inequilateral; valves striated, not ribbed; distinguished from the Cardita by having three teeth beneath the apices, and a callous lengthened tooth or ridge. Inhabits the coast of Guinea and California. Five living species. Three fossil.

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

· · · · ·

C. Californica.*

4. Genus _Hiatella_. Pl. VII.

_Animal._ Unknown.

_Shell._ Thin, elongated, subrhomboidal, equivalve, very inequilateral, gaping at its inferior edge, and at its posterior extremity; summit very anterior, and much flexed to the front; hinge formed of a single tooth upon one valve corresponding to an emargination in the opposite valve, or of a small tooth with a cardinal pit upon each valve; ligament exterior and dorsal. Inhabits the British seas. Two species.

Hiatella Arctica. H. biaperta.

5. Genus _Isocardia_. Pl. VIII.

_Animal._ Body very thick: edges of the mantle finely papillaceous, separated inferiorly, and united behind by a transverse band, pierced with two orifices surrounded with radiating papillæ; foot small, compressed, trenchant.

_Shell._ Free, regular, inflated, equivalve, very inequilateral, with diverging summits, strongly flexed anteriorly and outwardly, in a commencing spiral, hinge dorsal, long, similar, formed of two flat cardinal teeth and one lamellous behind the ligament; ligament dorsal, exterior, diverging anteriorly towards the summit; muscular impressions very distant and small. Inhabits the Mediterranean and British seas. Four living species. One fossil.

Isocardia Moltikana. I. retusum. I. cor. I. semisulcata.

FAMILY XI.

ARCACEA. Four Genera.

1. Genus _Arca_. Pl. VIII.

_Animal._ Body thick, slightly variable in form; abdomen provided with a pedunculated foot, compressed, fit for adhesion, and cleft throughout its extent; mantle supplied with a simple row of cirri and slightly prolonged posteriorly; buccal tentacula very small and very thin.

_Shell._ Somewhat diversiform, but most usually elongated and more or less oblique at the posterior extremity, often very inequilateral; summits more or less distant and little flexed to the front; hinge anomalous, straight, or a little flexed, long, and formed by a line of short vertical teeth, decreasing from the extremities to the centre; ligament exterior, wide, nearly as much before as behind the summit; two muscular impressions united by a band or palleal impression, not very distinct. Inhabits the American and British seas. Forty-one living species. Nine fossil.

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

· · · · ·

A. ponderosa.* A. pexata.* A. incongrua.* A. transversa.*

2. Genus _Cucullæa_. Pl. VIII.

_Animal._ As above.

_Shell._ Trapeziform, inequilateral, equivalve, heart-shaped; beaks far apart, 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 minutely striated longitudinally; margins crenulated. The Cucullæa is distinguished from the Arca by the muscular impression, to one side of which is an auriform testaceous appendage; the shell also is more trapeziform. Inhabits the Indian ocean. One living species. One fossil.

Cucullæa auriculifera.

3. Genus _Pectunculus_. Pl. VIII.

_Animal._ Body round, more or less compressed; mantle without cirri or tubes; foot securiform, cleft at its inferior anterior edge; buccal appendages linear.

_Shell._ Orbicular, equivalve, subequilateral; summit nearly vertical, and more or less distant; hinge formed upon each valve, of a numerous series of small teeth disposed in a curved line, sometimes interrupted beneath the summit; ligament as in Arca, but usually much narrower. Inhabits the British and Mediterranean seas. Twenty-two living species. Nine fossil.

Pectunculus pilosus. P. marmoratus. P. Pennaceus. P. castaneus. P. angulatus. P. palleus. P. zonalis. P. glycimeris. P. undulatus. P. scriptus. P. stellatus. P. violacescens. P. aggregatus. P. striatularis. P. pectinatus. P. rubeus. P. pectiniformis. P. nummarius. P. radiatus. P. vitreus. P. inscriptus. P. cinerosus.

4. Genus _Nucula_. Pl. VIII.

_Animal._ Body subtriquetral; mantle open in its inferior half only, with whole edges, denticulated throughout the extent of the back, without posterior prolongation; foot very large, thin at the root, enlarged into a wide oval disk, the edges of which are furnished with tentacular digitations; anterior buccal appendages, pretty long, pointed, stiff, and applied one against the other like jaws; the posterior ones also stiff and vertical.

_Shell._ More or less thick, subtriquetral, equivalved, inequilateral, with summits contiguous and inclined anteriorly; hinge similar, formed by a numerous series of very sharp teeth, pectinated and arranged in a line interrupted under the summit; ligament internal, short, inserted in a little oblique pit in each valve; two muscular impressions. Inhabits the British and American seas. Forty-five living species. Four fossil.

Nucula lanceolata. N. pella. N. obliqua. N. elongata. N. tellinoides. N. crenifera. N. Arctica. N. curvirostra. N. glacialis. N. fluviatilis. N. minuta. N. para. N. Mauritania. N. rostrata. N. Nicobarica. N. Margaritacea. N. Costellata. N. gibbosa. N. eburnea. N. polita. N. nasuta. N. fabula. N. Elenensis. N. cuneata. N. striata. N. rugulosa. N. Limatula. N. lævis. N. concentrica. N. decussata. N. exigua. N. squamosa. N. gigantea. N. nitida. N. tenuis. N. convexa. N. Pisum. N. carinifera. N. torta. N. plicaria.

· · · · ·

N. navicularis.* N. tenuisulta.* N. proxima.* N. acuta.* N. myalis.*

FAMILY XII.

TRIGONACEA. Two genera.

1. Genus _Trigonia_. Pl. VIII.

_Animal._ Entirely unknown.

_Shell._ Subtrigonal or suborbicular, thick, regular, equivalve, inequilateral; summits but slightly prominent, little flexed, anterodorsal; hinge complex, dorsal, dissimilar; two thick oblong teeth joined angularly under the summit, strongly furrowed upon the right valve, penetrating into two excavations of the same form, also furrowed, in the left valve; ligament postapicial; two distinct muscular impressions, not united by a band. Inhabits the Australian seas. One living species. Fifteen fossil.

Trigonia pectinata.

2. Genus _Castalia_. Pl. VIII.

_Animal._ Body large, slightly compressed, or moderately thick, more or less oval; mantle with thick edges, simple or broken, open in all its circumference except towards the back a kind of small, incomplete tube, furnished with two rows of somewhat elongated cirri for the respiratory cavity; flamelliform and trenchant.

_Shell._ Subtrigonal, equivalve, inequilateral; umbones eroded, covered with epidermis, and flexed anteriorly; hinge with two lamellar teeth transversely striated, one distant, posterior and shortened, the other anterior, long, and lateral; ligament exterior. Habitation unknown. One species.

Castalia ambigua.

FAMILY XIII.

NAIADEA. Four genera.

1. Genus _Unio_. Pl. VIII.

_Animal._ See _Castalia_.

_Shell._ Usually very thick, nacred within, covered with epidermis, corroded at the summits, which are dorsal and subanterior; dorsal hinge formed by a double precardinal tooth, more or less compressed, irregularly dentated on the left valve, and simple on the right, together with a long lamellous tooth under the ligament: ligament external, dorsal, and postapicial; two muscular impressions, well marked, besides those of the retractile muscles. The species of this genus grow more numerous daily; they are found in all countries, but particularly in North America. One hundred and sixty-seven defined species. Numerous fossil.

Unio Batayus. U. crassissimus. U. elongatus. U. litoralis. U. pictorum. U. platyrhynchus. U. marginalis. U. tigris. U. Egyptiacus. U. Niloticus. U. Leaii. U. crassidens. U. obliquus. U. plicatus. U. purpuratus. U. radiatus. U. rectus. U. retusus. U. rotundatus. U. Australis. U. Nova Hollandica.

The following species are American:

Unio Bengalensis. _Lea._ U. bilineatus. „ U. lamellatus. _Lea._ U. Morchisonianus. „ U. cæruleus. _Lea._ U. corrugatus. „ U. Corrianus. „ U. Graianus. „ U. alatus. „ U. andontoides. „ U. Augustatus. „ U. apiculatus. „ U. arcæformis. „ U. arctior. „ U. asperimus. „ U. asper. „ U. Blandingianus. „ U. Barnesianus. „ U. brevidens. „ U. camelus. „ U. capsæformis. „ U. carbonarius. „ U. castanus. „ U. Claibornensis. „ U. circulus. „ U. occineus. „ U. compressus. „ U. complanatus. „ U. confertus. „ U. congaræus. „ U. contradens. „ U. Cooperianus. „ U. creperus. „ U. cuprinus. „ U. Cumberlandicus. „ U. decisus. „ U. dolabriformis. „ U. donaciformis. „ U. Dorfeuillianus. „ U. uromas. „ U. ebenus. „ U. elegans. „ U. olivarus. _Lea._ U. ponderosus. „ U. divaricatus. „ U. acutissimus. „ U. fabalis. „ U. Fisherianus. „ U. folliculatus. „ U. fulvus. „ U. gibber. „ U. glaber. „ U. glans. „ U. globosus. „ U. graniferus. „ U. Griffithianus. „ U. Haysianus. „ U. heterodon. „ U. Hildrethianus. „ U. Hopetonensis. „ U. Hydianus. „ U. inflatus. „ U. interruptus. „ U. iris. „ U. irroratus. „ U. Jayensis. „ U. jegunus. „ U. Katherinæ. „ U. Kirklandianus. „ U. lævissimus. „ U. lacrymosus. „ U. lancolatus. „ U. Lecontianus. „ U. lens. „ U. lugubris. „ U. luteolus. „ U. Medellinus. „ U. Menkianus. „ U. metanever. „ U. Mühlfeldianus. „ U. ellipsis. _Lea._ U. multiradiatus. „ U. modiolioformis. „ U. notatus. „ U. Novi-Eboraci. „ U. obesus. „ U. obscurus. „ U. occidens. „ U. palliatus. „ U. patulus. „ U. stapes. „ U. perdix. „ U. perplexus. „ U. pictus. „ U. pileus. „ U. pliciferus. „ U. pulcher. „ U. pumilis. „ U. pustulatus. „ U. pustulosus. „ U. pyramidatus. „ U. Rangianus. „ U. Ravenelianus. „ U. Roanokensis. „ U. rubiginosus. „ U. Schoolcraftensis. „ U. securis. „ U. Shepardianus. „ U. simus. „ U. solidus. „ U. Sowerbianus. „ U. spinosus. „ U. splendidus. „ U. multiplicatus. _Lea._ U. subovatus. „ U. subrotundus. „ U. sulcatus. „ U. Taitianus. „ U. Tampicoensis. „ U. Tappanianus. „ U. tenuissimus. „ U. trapezoides. „ U. trigonus. „ U. Troostensis. „ U. turgidus. „ U. Vanuxemensis. „ U. varicosus. „ U. Vaughanianus. „ U. venustus. „ U. Watercensis. „ U. Zeiglerianus. „ U. zigzag. „ U. alatus. _Say._ U. apiculatus. „ U. camptodon. „ U. cariosus. „ U. crassus. „ U. cylindricus. „ U. declivis. „ U. dehiscens. „ U. monodontus. „ U. nasutus. „ U. ovatus. „ U. personatus. „ U. subtentus. „ U. tetralasmus. „

2. Genus _Hyria_. Pl. VIII.

_Animal._ As above.

_Shell._ Solid, nacred, equivalve, obliquely triangular, auriculated; base straight and truncated; hinge with two projecting teeth, the cardinal divided into numerous radiations, anterior ones smaller, the others lamellar and long. Inhabits the lakes and rivers of America. Two species.

Hyria avicularis.* Hyria corrugata.*

NOTE.—_Alasmidonta._ Separated by Say from the Anodonta by its primary tooth, and from the Unio by being destitute of the lamelliform teeth.

_Shell._ Transverse, equivalve, inequilateral; hinge with a primary tooth in each valve; cicatrices three. Four species.

Alasmidonta undulata. A. ambigua. A. marginata. A. confragosa.

3. Genus _Anodonta_. Pl. VIII.

_Animal._ As above.

_Shell._ Rather thin, regular, close, equivalve, inequilateral; summit anterodorsal; hinge entirely without teeth, with a postapicial lamina; ligament external, dorsal, and postapicial, two well marked muscular impressions, besides those of the retractile muscles. Inhabits fresh-water lakes in Europe and America. Forty-nine living species; and many fossil.

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

The following species are American.

Anodonta magnifica. _Lea._ A. Woodiana. „ A. angulata. „ A. Benedictensis. „ A. cylindracea. „ A. decora. „ A. edentula. „ Anodonta gigantea. _Lea._ A. incerta. „ A. Pepiniana. „ A. plana. „ A. salmonia. „ A. Stewartiana. „ A. subcylindracea. „ A. Ferussacina. _Lea._ A. fluviatilis. „ A. Newtonensis. „ A. Nuttalliana. „ A. Oregonensis. „ A. ovata. „ A. pavonia. „ A. Wahlamatensis. „ A. Wardiana. „ A. gibbosa. _Say._ A. grandis. „ A. impura. „ A. suborbiculata. „ A. undulata. „ A. lugubris. „

4. Genus _Iridina_. Pl. VIII.

_Animal._ As above.

The principal difference between the Anodonta and the Iridina, consists in the tuberculated hinge of the latter.

_Shell._ Thin, oval, much elongated, inauriculated; hinge very long, linear, and crenulated throughout its length, ligament external and marginal; two distinct muscular impressions. Inhabits the Nile and American coasts. Six species.

Iridina exotica. I. Nilotica.

· · · · ·

I. cælistis.* I. rubens.* I. elongata.* I. McMurtria.*

FAMILY XIV.

CHAMACEA. Three genera.

1. Genus _Diceras_. Pl. VIII.

_Animal._

_Shell._ Inequivalve, adherent; beaks conical, very large, diverging in irregular spiral contortions; hinge with a large, thick, concave, subauricular tooth in the larger prominent valve; two muscular impressions. One species. Fossil.

Diceras arietina.

2. Genus _Chama_. Pl. VIII.

_Animal._ Body suborbicular terminated superiorly by a sort of hook; mantle very slightly opened for the passage of a foot, terminated at its extremity by a part much narrower than the base; superior lobes of the branchiæ very short.

_Shell._ Irregular, adhering, inequivalve, inequilateral; summits more or less twisted spirally, especially in the lower valve by which these animals have the faculty of affixing themselves to other bodies; hinge dissimilar, thick, formed by a single lamellous tooth arcuated, subcrenulated, postcardinal and articulated in a furrow of the same form; ligament anterior and postapicial; two large muscular impressions, distant. British and American seas. Eighteen living species.

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

· · · · ·

C. exogyra.* C. Florida.*

3. Genus _Etheria_. Pl. VIII.

_Animal._ Unknown.

_Shell._ Adhering, irregular, thick, much nacred, inequilateral, inequivalve; summits subcephalic, thick, indistinct, in a species of heel, growing longer with age; hinge without teeth, callous, irregular and thick; ligament subdorsal in the exterior portion of the shell, and prolonged to a point internally; two irregular oblong muscular impressions, one superior and subposterior, the other inferior and anterior, with a marginal palleal impression. Inhabits the Indian Ocean. Five species.

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

FAMILY XV.

TRIDACNEA. Two genera.

1. Genus _Tridacna_. Pl. VIII.

_Animal._ Body somewhat thick; edges inflated, lobes of the mantle adhering, and united in nearly all their circumference, so as to present but three apertures, the first inferior and anterior, for the egress of the foot; the second superior and posterior for the bronchial cavity, the third much smaller and in the middle of the dorsal edge; two pairs of labial appendages, thin, nearly filiform, in the middle of which is a very small buccal orifice; branchiæ long and narrow; abdominal muscular mass considerable, and giving issue, as if from a cup, to a thick bundle of byssoid muscular fibres.

_Shell._ Thick, solid, of variable size, regular, triangular, inequilateral; summits inclined posteriorly, hinge dissimilar, entirely anterior to the summit; a lamellous precardinal tooth and two distant lateral teeth upon the left valve, corresponding with two precardinal lamellous teeth, and one distant lateral tooth upon the right valve; ligament anterior, elongated; a large, bifid, submedian muscular impression; another anterior one smaller and less distinct. Inhabits the Indian Ocean. Seven living species. One fossil.

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

2. Genus _Hippopus_. Pl. VIII.

_Animal._ As above.

_Shell._ More elongated and inequilateral than in the _Tridacna_, the anterior side being longer than the posterior; the posterior slope closed with a dentated margin. Inhabits the Indian seas. One species.

Hippopus maculatus.

FAMILY XVI.

MYTILACEA. Three genera.

1. Genus _Mytilus_. Pl. VIII.

_Animal._ Body oval, somewhat inflated; mantle open in its inferior half only, and terminated posteriorly by an oval cleft with fringed edges; a linguiform, canaliculated, abdominal appendage, with a byssus at its base behind, and several pairs of retractile muscles; mouth with simple lips; two contractile muscles, of which the anterior is very small.

_Shell._ Of a serrated tissue, elongated, more or less oval, sometimes subtriangular, equivalve, summits anterior, more or less curved, sloping inferiorly in a slight degree; hinge toothless, or with two very small rudiments; ligament dorsal, linear, subinterior, inserted in a narrow and very long furrow; two muscular impressions, of which the anterior is very small, besides those of the retractile muscles. Inhabits the British and American seas. Forty-two species.

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

· · · · · M. hamatus.* M. croceus.* M. cubitus.* M. lateralis.* M. Californianus.* M. leucophœatus.*

2. Genus _Modiola_. Pl. VIII.

_Animal._ As above.

Separated by Lamarck from the Mytilus, on account of its being more transverse than longitudinal, the beaks instead of being terminal are placed beneath the apex.

_Shell._ Smooth, subtransverse, equivalve, regular, subtriangular, posterior side short; summits nearly lateral; hinge toothless, linear and lateral; ligament partly interior, situated in a marginal furrow; one sublateral, elongated muscular impression in each valve. Inhabits the British and American seas. Thirty-two species.

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

· · · · ·

M. Americana.* M. castanea* M. opifex.* M. capax.* M. recta.* M. Carolinensis.* M. semi-costata.*

3. Genus _Pinna_. Pl. VIII.

_Animal._ Body oval, elongated, moderately thick, enveloped in a mantle closed above, open below, and especially to the rear, where it forms sometimes a sort of tube furnished with tentacular cirri: a flabelliform abdominal appendage, and a very considerable byssus; mouth provided with double lips, beside two pairs of labial appendages; a single large retractile muscle apparent.

_Shell._ Subcornate, fibrous, brittle, regular, equivalve, longitudinal, triangular, pointed anteriorly, in which direction is the summit, which is straight, wide, and frequently truncated posteriorly; hinge dorsal, longitudinal, linear, toothless; ligament occupying nearly all the dorsal edge of the shell; a single and very wide muscular impression posteriorly; a trace of the anterior in the summit. Inhabits the Mediterranean Sea. Fifteen species.

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

FAMILY XVII.

MALLEACEA. Five genera.

1. Genus _Crenatula_. Pl. VIII.

_Animal._ Unknown.

_Shell._ Irregular, much flattened, subrhomboidal, subequivalve, gaping posteriorly; summit anterior; hinge longitudinal, dorsal, toothless; ligament submultiple, or inflated from place to place, and inserted in a series of round cavities corresponding with the dorsal edge; muscular impression unique and subcentral. Inhabits the Red Sea. Seven species.

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

2. Genus _Perna_. Pl. VIII.

_Animal._ Body much compressed, the mantle prolonged posteriorly in a sort of lobe, and fringed at its inferior edge only; a byssus; a single contractile muscle.

_Shell._ Irregular, much compressed, subequivalve, form somewhat variable, gaping at the anterior part of its inferior edge; summit very small: hinge straight, vertical, buccal, toothless; ligament multiple, and inserted in a series of longitudinal and parallel furrows; a subcentral muscular impression. Inhabits the Indian seas. Ten species living. Two fossil; one found in France and one in Virginia.

Perna ephippium. P. isognomon. P. femoralis. P. marsupium. P. obliqua. P. sulcata. P. vulsella. P. nuclea. P. avicularis. P. canina.

3. Genus _Malleus_. Pl. VIII.

_Animal._ Imperfectly known, but certainly byssiferous, with a single retractile muscle.

_Shell._ Subnacreous, irregular, subequivalve, inequilateral, generally much auriculated anteriorly, and prolonged posteriorly into the body, so as to present some resemblance to a hammer; summits entirely anterior; between them and the inferior auricle, an oblique slope for the passage of the byssus; hinge linear, very long, buccal, toothless; ligament simple, triangular, inserted in a conical oblique pit, partly external; a moderately large subcentral muscular impression. Inhabits the Australian seas. Six species.

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

4. Genus _Avicula_. Pl. IX.