Part 6

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.