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Show 398 MOLLUSCA. third plate that is sometimes stony and sometimes horny, by which the animal adheres to foreign bodies, and the remainder of it (the muscle) serves to join one valve to the other. The animal,-EoHroN Poli, has a small vestige of a foot, similar to that of a Pecten, which slips between the emargination and the plate that closes it, and perhaps serves to direct water to the mouth which is close to it(l). These shells al'e found attached to various bodies like the Ostrea:!. They are found in every sea(2). PLACUN A, Brug. A small genus allied to the Anomire, in which the valves are thin, unequal, and frequently irregular, as in the latter, but both entire. Two projecting ribs, en chevron, are seen on the inside of one of them, near the hinge. The animal is not known, but it must resemble that of the Ostrero, or that of the Anomire(3). SPONDYLus, Lin. A rough and foliaceous shell as in the Ostrere, and frequently spiny; but the hinge is more complex; besides the cavity for the ligament, analogous to that of the Ostrere, there arc two teeth to each valve that enter into fossre in the opposite one; the two middle teeth belong to the most convex valve, which is usually the left one, and which has a projecting heel, flattened as if sawed through behind the hinge. The animal, like that of a Pecten, has the borders of its mantle furnished with two rows of tentacula, some of the external ones being terminated by coloured tubercles; before the abdomen is a vestige of a foot formed ~e a broad radiated disk on a short pe· dicle, and endowed with the faculty of contraction and expansion(4). From its centre hangs a filament, terminated by an oval mass, the use of which is unknown. The Spondyli are eaten like oysters. Their shells are ft·equently (1) This foot escaped the notice of M. Poli. (2) .O.nomia epltippium, Gm. ;-.9.. cepa,·-.9.. elect1·ica;-Jl.. squamula;-.11. acu· leata,·-Jl.. squama,·-.9.. punctata,·-.9.. undulata,·-and the species added by Bru· gieres, Encyc. Method., Vers., I, 70, et seq.; and pl. 170, 71. The other .O.nomice of Gmelin arc Placunce, Ter.ebratulce, and Hyalm. (3) .O.nomia placenta, Chemn., VIII, lxxix, 7i6;-JJ.n. sella, lb., 714. See also pl. 173 ancll74, Encyc. Method., Vers. ( 4) Called by Poli "the abdominal tracltea" in the Spondyli, &c. ACEPHALA TEST ACEA. 399 tinged with the most brilliant colours. They adhere to all sorts of bodies( 1 ). PuoATULA, Lam. The Plicatulre, separated by Lamarck from the Spondyli, have nearly the same kind of hinge but no heel, and flat, almost equal, irregular, plicated and scaly valves, as in many of the Ostrere(2). MALLEus, Lam. A simple pit for the ligament as in the Ostrere, where the Mallei were left by Linmeus, on account of their having the same irregular and inequivalve shell, but distinguished by a notch on the side of this ligament for the passage of a byssus. The most known species, Ostrea malleus, L.; Chemn., VIII, Ixx, 655, 656, which ranks among the number of high-priced and rare shells, has the two ends of the hinge extended and forming something like the head of a hammer, of which th~ valves, elongated in a transverse direction, represent the handle. It inhabits the Archipelago of India. There are some others, possibly young ones of the same species, in which the hinge is not prolonged. We must be careful not to confound them with the Vulsellre(s). VuLSELLA, Lam. A little salient plate inside of the hinge of each side, from one of which to the other extends the ligament, otherwise similar to that of the Ostrere. By the side of this plate is a notch for the byssus, as in the Mallei. The shell is elongated in a direction perpendicular to the hinge. The most known species inhabit the Indian Ocean( 4). PERNA, Brug. Several parallel cavities across the hinge, opposed to each other in (1) Spondylus gcederopus, Chemn., VII, xliv, et seq., IX, cxv;-Sp. regius, Id., xlvi, 471. (2) Spond. plicatus, L., Chern. VII, xlvii, 479, 482;~Plicat. cegyptia, Savign., Egyp. Coq., pl. xiv, f. 5. (3) Oatrea vulsella, Chemn., VIII, lxx, 657, of which the Ostrea anatina, lb. 658, 659, is probably a mere accidental variety. (4) Myavulsella, Chemn., VI, ii, 10, 11;-V. spongiarum, Lam., Savig., Eg., Coq, pl. xiv, f. 2;-V. Mans, Lam., Sav., lb., f. 3. |