Elements of conchology Prepared Elements of conchology / Prepared for the use of schools and colleges elementsofconcho00rusc Year: 1844 PALUDINA.—LITTORINA—MONODON. 49 Fig. 49. PALUDINA. 37. The tribe of Hemi'cyclo'stoma is composed of pectini- branch gasteropods, which resemble snails in the form of their shell, of which the whorl next to the last presents a sunken arch, which gives its aperture more or less resemblance to a crescent. They form many genera, among which we will mention the Palvdina, Littorina, Monodonta, Janthina, and Nerita. 38. The Paludin^ were, for a long time, confou
Elements of conchology Prepared Elements of conchology / Prepared for the use of schools and colleges elementsofconcho00rusc Year: 1844 PALUDINA.—LITTORINA—MONODON. 49 Fig. 49. PALUDINA. 37. The tribe of Hemi'cyclo'stoma is composed of pectini- branch gasteropods, which resemble snails in the form of their shell, of which the whorl next to the last presents a sunken arch, which gives its aperture more or less resemblance to a crescent. They form many genera, among which we will mention the Palvdina, Littorina, Monodonta, Janthina, and Nerita. 38. The Paludin^ were, for a long time, confounded with the cyclostomse, but the aperture of their shell is without the rolled lip, and they are provided with branchise for breathing in water ; they show the first vestiges of the syphon which always exists in the follow- ing family; we observe on each side of the body a sort of membranous wing, and on the right side this prolongation curves into a small canal, through which water is introduced into the branchial cavity. Many species are found in fresh waters in the United States. A common species, the Palvdina vivi'para, so called because its young are born alive, is marked by purplish longitudinal bands, and the shell is greenish ; it abounds in the standing waters of France. 39. The Littorina do not differ much from the Paludinse, except that they have a thicker shell, and inhabit the sea. The Vigneau, or Turbo littoreus, the shell of which is round, of a brown colour, streaked with black, belongs to this genus ; it abounds on the coast of France, where it is eaten by the natives. 40. The MoNODONs are distinguished from the littorinse by the presence of a blunt, slightly projecting tooth at the base of the columella. The animal generally bears on each side three or four filaments, as long as the tentacles, and has the eyes supported on peculiar pedicles. A small species, the Trochvs tesselatvs, with a brown shell, spotted whitish, abounds on the coasts of France.
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