Acera Carnosa.
2. Bullæa. One species.
Formerly classed with the Bulla, but separated from it on account of the shell being entirely covered by the animal, and never externally visible.
Shell oval, thin, fragile, more or less involuted on one side, rendering the aperture more or less wide.
B. aperta. The open Bullæa. Pl. [17], fig. 5.
Shell interior and very incompletely involuted, without spire or columella; sub-orbicular, white, transparent, faintly striated, and slightly wrinkled; almost entirely open.
3. Bulla. The Bubble. Eleven species.
The great confusion that existed in this genus, as classed by Linnæus, has been elucidated by the division and classification of Lamarck. This genus derived its name from the resemblance which some of the smaller species have to a bubble of water. Its shells are found in almost all parts of the world.
Shell external, oval, involuted; aperture very large, open the whole length of the shell, and generally wider at the base; outer edge sharp and smooth; summit umbilicated.
Bulla lignaria.