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Show 336 MOLLUSCA. ONcHIDIUM, Buchan.(l) A broad fleshy mantle, in the form of a shield, overlapping the foot at all p~ints, and even covering the head when it contracts; two long retractile tentacula, and on the mouth an emarginated veil, formed of two triangular and depressed lobes. The anus and respiratory orifice are under the posterior edge of the mantle, where, a little more deeply, we also find the pulmonary cavity. Close to them, on the right, opens the female organ of generation, that of the male, on the contrary, is under the right great tentaculum, the two openings being united by a furrow, which extends along the under part of the whole of the right margin of the mantle. These animals, destitute of jaws, have a muscular gizzard, followed by two membranous stomachs. Several of them inhabit the sea-shore, but in places where the ebb leaves them uncovered, so that they can readily breathe the natural air(2). The aquatic Pulmonea, with complete shells, were also placed by Linnreus in his genera HELIX, BuLLA and yoLUTA, from which it has been found necessary to separate them. In the first were comprised the two following genera, where we find the internal edge of the aperture crescent-shaped, as in Helix. PLANORBis, Brug.(3) The Planorbes had already been distinguished from the Helices by Brugieres, and even previously by Guettard, on account of the slight increase of the whorls of their shell, the convolutions of which are (1) 0Ncnxmux, a name given to thilil genus because the first species (Oncltidium typhre, Buchan., Lin. Soc. Lond., V, 132) was tuberculous; I now know one that is smooth, the Oncltidiwm lrevigatwm, Cuv., and four or five that are tuberculous: Oncl~. Peronii, Cuv., Ann. du Mus., V, 6;-0nclt. Sloanii, Cuv., Sloane, Jam., pl. 273, 1 and 2;-0nclt. verruculatum, Descr. de l'Eg., Moll. Gaster., pl. ii, f, 3;- 0nclt. celticum, Cuv., a small species from the coast of Brittany. N.B. M. de Blainville has changed the name of Onchidium into that of PtnoNU, and applied the former to the Vaginula:. These Peronia: he places among his CYCLOllRA.NcnuTA., but I can sec no 1·eal difference between their respiratory organ and that of the other Pulmonere. (2) See Chamisso., Nov. Act. Nat. Cur., XI, part I, p. 348, and Van Hassel., Bullet. Univers., 1824, Sept., Zool., 83. (3) Hel. vortex;-H. cornea;-/{. spi1·orbis;- ll. polygyra;-H. contorta;-H· nitida;-H. alba;-H. similis, GASTEROPODA PULMONEA. 337 nearly in one plane, and because the aperture is wider than it · I . . 18 big~. t contams a~ ammal with long, thin, filiform tentacula, at the mner base of whtc~ are the eyes, and from the margin of whose mantle exudes a qua~tlty of a red flu.id, which is not, however, its blood. Its stomach lS muscular and lts food vegetable like that r the Limnrei, of which, in all our stagnant waters, it is' the faithf~l companion. The · LIMN.tEus, Lam.(l) Separated from the Bulirni of Brugiere by M. Delarnark, has, like a Bulimus, an oblong spine and the aperture higher than it is wide· but the margin, like that of a Succinea, is not reflected, and ther~ is a longitudinal fold in the columella, which runs obliquely into the cavity. The shell is thin; the animal has two compressed broad tr1. angu 1a r tentacu 1a , near the base of whose inner edge are t'h e eyes., They feed on plants and seeds, and their stomach is a very muscular gizzard, preceded by a cl'op. Like all the Pulmonea, they are hermaphrodites, and the female organ of generation being far from the other, they are compelled so to copulate, that the individual which acts as a male for one; serves as a female for a third; long strings of them may be observed in this position. They inhabit stagnant waters in great numbers; they also abound with the Planorbes in certain layers of marl or calcareous strata which they evidently prove were deposited in fresh water(2). ' PuYsA, Drap. The Physre, which were gratuitously placed among the Bullre, have a shell very similar to that of a Lymnrea, but without the fold in the columella and reflected edge, and very thin. When the animal swims or crawls, it covers its shell with the two notched lobes of its mantle, and has two long, slender and pointed tentacula, on the greatly enlarged internal base of which are the eyes. They inhabit springs, &c. One of them, Bulla fontinalia, L., which is sinistral, is found in France(3). See the quotations of Gmel., and add, Draparnaud, pl. I, f. 39-51, and pl. ii, f.l-22. (1) Hel. Jtagnalis, L., of which H. fragilis is a variety;-H. paluatria;-H. peregra;- H. limosa,·-H. auricularia. See Drap., pl. ii, f. 28, 42, and pl. iii, f. 1, 7. (2) The mantle of the Limn. glutinosus, like thnt of the Phys<l:, is sufficiently ample to envelope its shell. I tis the genus AxPihPEPLEA., Nilson, Moll. succ. ~3~ The neighbouring species, Bull. hyprurrwm, L., and Phyaa acuta, and Scatlll'lg& num, Drap., require an examination of their animals. Jlide, Drap., p. 54, et seq. VoL. II.-2 S |