"Calyptræa is very thin and brittle, with an internal lip. (See Frontispiece.)
"Crepidula has the shell partly covered, or arched: it looks like a little slipper.
"Ancylus spina-rosa is a pretty species from the south of France: the genus is fluviatic. A. lacustris and fluviatilis are both natives of our fresh-waters.
"The next family, Bullæana, has
| Acera | Bulla. |
| Bullæa | Bulla. |
| Bulla | The same. |
"Acera and the following genus have each but one species, Bulla carnosa and B. aperta of Linnæus. The original genus Bulla was composed of an assemblage of shells of various characters, having little resemblance except in their gibbous form. Bulla naucum is an example of the genus of Lamarck's system; so is B. lignaria. (See Frontispiece.) B. ampulla and B. striata are common in collections.
APLYSIA.
DOLABELLA.
"Aplysiana is a small family, containing