Calyptraea

Calyptraea, commonly known as the `Chinese hat snails` is a genus of sea snails, marine gastropod mollusks in the family Calyptraeidae, a family which contains the slipper snails or slipper limpets, cup-and-saucer snails, and Chinese hat snails. Species within the genus Calyptraea include: ...
Found on http://en.wikipedia.org/wiki/Calyptraea

Calyptraea

Calyptraea is a genus of gastropod molluscs which includes forms presenting some resemblance in habits and external appearance to the limpets, to which they are not nearly related. Externally the shell appears simple and cap- shaped, but beneath the apex there is a concealed inner whorl.
Found on http://www.probertencyclopaedia.com/browse/BC.HTM
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