| OCR Text |
Show 360 MOLLUSCA. 'Same way above the head by a great so~ution of continuity; the sexes are separated; the penis of the male IS large, fleshy.' and reflected into the pectoral cavity; the two tentacula are termmated by blunt tubercles, and two other tubercles, placell on their external base, support the eyes. The shell is a spiral oval, with complete whorls, transversely and finely striated, and its apet·ture, in the adult, is surrounded with a small ridge. It is closed by a small round operculum. Found in woods, under moss, stones, &c. The most common is the Turbo elegans, List., 27, 25, about six. lines in length and of a greyish colour; found under all the mos'Ses(I). VALVATA1 Mull. The Valvatre inhabit fresh water; theit· shell is convoluted in almost one plane like that of a Planorbis, but the aperture is round, and furnished with an operculum; the animal, which has two slen· der tentacula, with the eyes at their antel'ior base, respires by means of branchice. In a species found in France, Valv. cristata, Mull.; Drap., I, 32, 33; Gruet-Huysen, Nov. Act. Nat. Cur. X, pl. xxxviii, the branchire, formed like a feather, project from under the mantle and float extet·nally, vibrating with the breathing of the animal. On the right side of the body is a filament which resembles a third tentaculum. The foot is divided, anteriorly, into two hooked lobes. The penis of the male is slender, and reflected into the branchial cavity. The shell, which is hardly three lines broad, is greyish, flat, and umbilicated. Found in stagnant water(2). It is here that we must place the completely aquatic shells, or those respiring by branchire, which belonged to the old genus HELIX ; i. e., those in which the penultimate whorl forms, as in the Helices, Lymmere, &c., a depression which gives the aperture more or less of the figure of a crescent(3). The three first genera are still closely allied to Turbo. (1) Add Turbo lincina, List., 26, 24;-T. labeo, List. 25, 23;-T. dubius,Born~ XIII, 5, 6;-T.limbatus, Chemn., IX, cxxiii, I07.i. We should distinguish, among the fossils, the Cyclostoma mttmia of Lam., Brongn., Ann. du Mus., XV, xxii, 1. (2) Add, Valvata planorbis, Drap., I, 34·, 35;-V. minuta, Id., 36-38. (3) They constitute the ELLIPSOSTOMA of M. de Blain ville. GASTEROPODA PECTINIBRANCHIAT A. 361 P ALUDIN A, Lam. This genus has lately been separated from the Cyclostomre, because there is no ridge round the aperture of the shell; because there is a a small angle to that aperture as well as to the operculum, and finally, because the animal, being provided with branchire, inhabits the water, like all other genera of this family. It has a very short snout and two pointed tentacula; eyes at the external base of the latter, but on no particular pedicle, and a small membranous wing on each side of the fore part of the body. The anterior edge of the foot is double, and the wing of the right side forms a little canal which introduces water into the respiratory cavity, the incipient indication of the siphon in the following family. The common species, Helix vivipara, L.; Drap., I, 16, whose smooth and greenish shell is marked with two or three purple, longitudinal bands, and which abounds in stagnant waters, in France, produces living young ones: in the spring of the year they may be found in the oviduct of the female, in every stage of development. Spallanzani assures us that if the young ones be taken at the moment of birth and be reared separately, they will reproduce without fecundation, like those of the Aphis. The males, however, are nearly as common as the females; they have a large penis which protrudes and retracts, as in Helix, but through a hole pierced in the right tentaculum, a cit•cumstance which renders that tentaculum appa1·ently larger than the other, and which furnishes us with a mode of recogni~ing the male(l). The Ocean produces some shells which only differ from the Paludinre in being thick. They form . the LITTORINA, Feruss., Of which the common species, Le Vigneau-Turbo littoreus, L., Chemn. V, clxxxv, 1852, abounds on the coast of France, where it is eaten. The shell is round, brown, and longitudinally streaked with blackish. The MoNO DON, Lam. Only differs from Littorina in having a blunt and slightly salient tooth at the base of the columella, which sometimes has also a fine notch. (1) Add: Cyclost. achatinum, Drap. I, 18;-C. impurum, ld,, 19, 20, or Helix tentaculata, L., &.c.; and the small species of salt-water ponds described by Beudan4 Ann. du Mus., XV, p. 199. VoL. Il.-2 V |
