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Show 382 MOLLUSCA. TuRBINELLA, Lam., Also consists of shells with a straight canal, but without varices, distinguishable by the large transverse plic:£ on their columella, which extend the whole length of the aperture, and which closely approximate them to the conical Volut:£; they only differ from the latter in the elongation of their aperture into a sort of canal( I); the line that separates them is not easily traced. The genus STROMBus, Lin., Includes those shells with a canal that is either straight or inflected towards the right, of which the external margin of the aperture dilates with age, but still preserves a sinus near the canal, under which pas.ses the head of the animal, when it extends itself. In most of them the sinus is at some distance fl'om the canal. They are subdivided by M. de Lamarck into two subgenera. The STROMBus, Lam. In which the margin expands into a wing of more or less extent, but not digitated. The foot is proportionably small, and the eyes are supported by lateral pedicles of the tentacula, thicker than the tentacula themselves. The operculum is horny, long and narrow, and placed on a thin tail(2). In the PTEROCERA, Lam. The mat·gin, in the adult, is divided into long and slcntlet· digita· tions, varying in number, according to the species. The animal is the same as that of the true Strombus(3). In other Strombi, the sinus of the external margin is contiguous to the canal, funning the RosTELLARIA, Lam. There is usually a second canal ascending the spire, formed by the external rnat·gin and by a continuation of the columella. 0) Mur. scolyrnus, Martini, lV, cxlii, 1325;-Voluta pyrum, Martini, Ill, xcv, 916, 917;-Voluta cerarnica, List., 829, 51;-Voluta rhinoceros, Chemn., X, 150, f. 1407, 1408;-Voluta turbinellus, List., Sll, 20;-Vol. capitellum, List., 810, 19;Vul. globulus, Chern., XI, 178, f., 1715;-Vol. tu?·rita, Gm. (2) Nearly all the St.rombi comprised in the second and third division of Gmelin, observing, that owing to the various degrees of development acquired by the ex· ternal margin, there a1·e several repetitions. (3) Strombus lambis, Rondel., 79; Martini, HI, lxxxvi, 855;-Stt·. cltimgra, List., 870;-Str. rnillepeda, list., 868, 869;-St?·. scwpius, List., 867. GASTEROPODA PECTINIBRANCHIAT A. 383 In some of them, the margin is still digitated. Their animal resembles that of a Murex, but has only a very small operculum( 1 ). In others, we merely observe a dentated margin. Their canal is long and straight(2). In some again, that margin is entire; they are the HIPPOORENEs, Montf.(3) ORDER VII. TUBULIBRANCHIA T A. The Tubulibranchiata should be detached from the Pectinibranchiata, with which they are very closely allied, because the shell, which resembles a more or less irregularly shaped tube, only spiral at the commencement, attaches itself to various bodies; they consequently are deprived of copulating organs, and fecundate themselves. In the V ERMETus, A dans., We remark a tubular shell whose whorls, at an early age, still form a kind of spire, but then continue on in a tube more or less irregularly contorted, or bent like the tubes of a Serpula. This shell usually attaches itself by interlacing with others of the same species, or is partly enveloped by Lithophytes: the animal, having no power of locomotion, is deprived of a foot, properly so called; but the part which in ordinary Gasteropoda forms the tail, is here turned under it, and extends to beyond the head, where its e.xtremity becomes inflated and furnished with a thin opet·culum; when the animal withdraws into its shell, it is this mass which closes the entrance; it is sometimes seen with various appendages, and in certain species, the operculum is spiny. The head of the animal is obtuse, and has two moderate tentacula, on the external sides of which, at the base, (1) Strombus pes pelecani, L., List., 865, 866. (2) Strombu~fusus, L., List., 854, 11, 12, 916, 9. (3) Strombus amplus, Brander., Foss., Hant., VI, 76, or Roatellaria macroptera, Lam.; Str.jissurella, Lam., Encycl. Method., p. 411, 3, a, b, which is not that of Martini, IV, ch·iii, 1498, 1499, &c. |