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Show 394 MOLLUSCA. greatly elongated. There is much incertitude however with t·espect to all these bodies(l ). As to the well known living testaceous Acephala, Linnmus had united in the genus OsTUEA, Lin., All those which have but a small ligament at the hinge, inserted into a little depression on each side, and without teeth or projecting plates. OsTREA, Brug. The true Oysters have the ligament as just described, and irregular inequivalve and lamellated shells. They adhere to rocks, piles, and even to each other, by their most convex valve. The animal-PELORis, Poli,-is one of the most simple of all the bivalves, possessing nothing remarkable but a double fringe round the mantle, the lobes of which arc only united above the head, near the hinge; but there is no vestige of a foot. 0. edul'is, L. The common oyster is well known to every one. Its fecundity is as astonishing as its flavour is delicious. Among the neighbouring species we may observe, 0. cristata, Poli, II, xx, or the little Mediterranean oyster. Among the foreign species we have, 0. parasitica, L.; Chemn., VIII, lxxiv, 681. Round and flat; it adheres to the roots of such mangroves and other trees of the torrid zone, as the salt-water can reach. 0. folium, L.; lb., lxxi, 662, 666. Oval; the margin plicated in zig-zag; it attaches itself by the indentations in the back of its convex valve to the branches of the Gorgonire and other Litho· phytes(2). M. de Lamarck separates by the name of (1) The observations of M. Desha yes and Audouin even lead us to believe tba4 in a part of these shells, there were two muscular impressions. (2} The various species of Oysters, on account of their irregularity, are not easily distinguished: to this genus are referred the Oat. orbicularia;-0. famica!a; -0. ainemia;-0. Forakahlii,--0. rostrata,--0. virginica;-0· cornucopire;-0. aenegalenais,--0. stellata;-0. ovalis;-0. papyracea, and the Mytilua crista·ga/Ji; -M. hyotis;-M. frons, Gmel., and those figured by Brugiet•e in the Encyc. Me· thod., pl. 179, 188. It is almost certain, however, that several of these pretended species are mere varieties. The Oat. aemi-aurita, Gualt., 84, H, is a young .!lviculahirundo. ACEPHAI. TESTACEA. 395 • GitYl1 II..t'EA, Lam., Certain oysters, mostly fossil, of the ancient calcareous and schistous strata, in which the summit of the most convex valve greatly projects and cu:ves more or less into a hook, ot· is partially spiral; the other valve IS frequently concave. The greater number of these shells appear to have been free; some of them, however, seem to have adhered to other bodies by theit· hook( 1 ). G. tricarinata. The only living species known. PEoTEN, Brug., The Pectens, very properly separated from the Oysters by Brugiere, although they have the same kind of hinge, arc easily distinguished by their ineq uivalvc semi-circular shell, almost always regularly marked with ribs, which radiate from the summit of each valve to the edge, and furnished with two angular productions called ears, which widen the sides of the hinge. The animal -ARous P ' ' , oh, has but a small oval foot(2) placed on a cylindrical pedicle be-fore a sac-like abdomen that hangs between the branchire. Some species, known by a deep emargination under their anterior ear arc furnished with a byssus. The others cannot adhere and even s~vim with rapidity by suddenly closing their valves. Th'e mantle is surrounded with two ranges of filaments, several of the external ones being tet·minated by a little greenish globule. The mouth has numerous branched tentacula in place of the four, usual, labial leaflets. The shell is frequently tinged with the most lively colours. The great species of the French coast, Ostrea maxima, L., has convex valves, one whitish, the other reddish, with fourteen ribs each, that are broad and longitudinally stdated. The animal is eaten. We may also remark the Sole of the Indian Ocean, Ostrea solea, Chemn., VII, lxi, 595, with extremely thin and almost equal valves, one brown, the other white, and internal ribs fine as hairs, approximated two by two(3). ' (l) SecBrug., Encyc. Metl10d., pl. 189. ( (2) Improperly styled by Poli the abdominal tracltea tha3 ) Add th e n·m ety-one spee1· es of Ostrea, Gmel.; we .m ust remember however t ~orne of them are fat• fi·om established on a solid foundation. Fo; the fossii iecles, consult Sowerby (Mineral Conchology), and Brongniart, App. Cuv., Oss. 081• tome IJ, Env. de Paris. |
