OCR Text |
Show 364 MOLLUSCA. bottom of the aperture, which seems to indicate a relation with the Terebrre of Brugieres( 1 ). In the PIRENA, Lam., We not only find this little sinus below, but likewise a second on the opposite side(2). These two subgenera, as well as the Melanire, inhabit the rivers of southern Europe and of all hot countries. There are two genera, detached from the Volutre, which, but that they are operculated and have but two tentacula, would resemble the Auriculre, that we think may come here, viz. AcTJEON, Montf.(3)-ToRNATELLA, Lam., Where the shell is elliptical, the spire but slightly salient, the aperture lengthened into a crescent and widened below, and the base of the columella marked by one or two large plicre or oblique callosi· ties( 4); and the PYRAMIDELLA, Lam. Where the spire is turreted, the aperture crescent-like and wide, and the base of the columella obliquely contorted and marked with sharp spiral plicre( 5). JANTHINA, Lam.(6) The form of the animal separates the Janthinre from all the precc· ding genera. Their shell, however, is similar to that of the terres· trial Limaces, the columellar margin being also indented, but slightly angular at the external edge, and the columella somewhat extended beyond the half-oval, which, without this prolongation, would be formed by that edge. (1) Melan. buccinoi'dea, Feruss., Mem. de la Soc. d'Hist. Nat. de Paris, tome I, pl. vii, f.l-11, &c. See Sowerby, No. XXII. (2) Pir. terebralis, Lam.; List., Tab. 115, f. 10;-Pir. maaagascariensiB, Encycl., pl. 458, f. 2, a, b, &c. (3) Which must be carefully distinguished from the .O.ctt£()'11,8 of Oken that ap· pear to be allied to the .O.plysit£. (4) Voluta.trrrnatilis, and bifasciata, L., Martini, II, xliii, 442, 443;-V. aulcato, and V. solidula, lb., 440, 441;-V. jlarnmea, lb., 439;-V. jlava, lb., 444;-P: pusilla, lb. 446. { 5) Trochus dolabratus, L. Chemn., V, clxvii, 1063, 1064;-Bulimus terebellum, Brug., List., 844, 72. (6) This genus forms the family of the OXTSTOME, Blainv. GASTEROPODA PECTINIBRANCHIAT A. 365 The animal has no operculum, but the under surface of its foot is furnished with a vesicular organ resembling a bubble of foam but composed of a solid substance, which prevents it from crawling' but allows it to ~oat on ~he surface of the water. The head, a cyli~drical proboscis, termmated by a vertically cleft mouth, and armed with little hooks, has a bifurcated tentaculum on each side. The common species, Helix Janthina, L.; List., 572, 24, has a pretty violet shell, and is very abundant in the Mediterranean. vyhen the animal is touched, it diffuses a thick fluid of a deep vwlet colour that dyes the surrounding water. NERITA, Lin.(l) The columella of the Neritre being in a straight line, renders the aperture semicircular or semi-elliptical. This aperture is generally large in comparison with the shell, but is always furnished with an operculum which completely closes it. The spire is almost effaced, and the shell semi-globular. NATioA, Lam. Neritre with an umbilicated shell; the animal of the species known has a large foot, simple tentacula with the eyes at their base, and a horny operculum(2). NERITA, Lam.-PELORONTA, Oken. The umbilicus wanting; shell thick, columella dentated, and operculum stony; the eyes of the animal on pedicles by the side of the tentacula, and a moderate foot(3). The V ELATA, Montf., Where the side of the columella is covered with a calcareous, thick and convex layer( 4), is distinguished from it, but perhaps without any good reason; also the N ERITINA, Lam., Where the shell has no umbilicus and is thin, with a horny oper- (1) M. de Blainville forms })is family of the HEMICYCLOSTOMJE, from this genus. (2) For the species see the first div. of Gm. and Chemn., V, pl. clxxxviclnxix. (3) Por the species see the third div. of Gm. and Chemn., V, pl. clxxxxclxxxxiii, and Sowerby, Gen. of Sh., No. XV. (4) Nerita perveraa, Gm., a large fossil species; Chemn., IX, cxiv, 97.'i, 976. |