The royal natural history . spawn ok periwinkle (magnified). GASTROPODS. 387 retracted within their shells. The spawn of this species is illustrated in the allied to the last is the genus Lacuna, in which the animal has long,slender tentacles, while on the upper part of the foot there are two lono-appendages, which extend much beyond its pointed extremity, The speciesillustrated occurs on the British coasts, and, like the periwinkles, feeds uponseaweeds. The so-called staircase-shells (Solariidce) are all formed much upon. horned winkle, Lacuna divaricata (enlai-ged). one and the
The royal natural history . spawn ok periwinkle (magnified). GASTROPODS. 387 retracted within their shells. The spawn of this species is illustrated in the allied to the last is the genus Lacuna, in which the animal has long,slender tentacles, while on the upper part of the foot there are two lono-appendages, which extend much beyond its pointed extremity, The speciesillustrated occurs on the British coasts, and, like the periwinkles, feeds uponseaweeds. The so-called staircase-shells (Solariidce) are all formed much upon. horned winkle, Lacuna divaricata (enlai-ged). one and the same plan. They are more or less conical, flattened, and umbilicatedbeneath, and nearly always beautifully sculptured. In Solarium the umbilicusis often very wide, and is bordered by a crenulated edge, winding upwards to theapex of the shell, and terminating in a notch upon the aperture. The embryonicshell is sinistral, and in the course of growth becomes turned spire-downwards,and, with the exception of its base, concealed by the succeeding whorls. Abouttwenty species are known, and are chiefly met with in tropical seas. In Toriniathe shells are more narrowly umbilicated, and not carinate at the margin likeSolariiwm, and the operculum is very remarkable, being conical,and consisting of many whorls. All the molluscs belonging to the Rissoidce are, very small. Theshells are something like a minute Littorina, but they are often longi-tudinally ribbed, a style of sculpture not met with in the are found everywhere,
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Keywords: ., bookcentury1800, booksubjectnaturalhistory, booksubjectzoology
