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.
B. ampulla.
B. striata.
B. naucum.
B. physis.
B. fasciata.
B. aplustre.
B. hydatis.
B. cornea.
B. fragilis.
B. solida.
_B. aplustre._ The streamer-like Bulla. Pl. 17, fig. 7.
Species completely involute; the spire very distinct, visible, but not
projecting, with a kind of thickening at the anterior part of the
columellar edge.
_B. lignaria._ The woodlike Bulla.
Species sub-involute, no visible spire either within or without, but
narrowed towards the top when it is slightly umbilicated; yellowish
brown colour, with transverse pale striæ.
_B. hydatis._ The watery Bulla.
Species more solid, thicker, almost entirely involute; whorls of the
spire slightly visible in an umbilicus projecting interiorly from the
summit.
_B. naucum._ The sea-nut Bulla.
Species thin; the whorls of the spire visible externally, but without
projection, and with a suture as if caniculated without thickening at
the anterior part of the columellar edge.
_B. fragilis._ The fragile Bulla.
Species very thin, rather involute; the whorls of the spire distinct
within as without; the suture deep, angular, and cleft in a greater or
less part of its length.
FAMILY V.
APLYSIACEA. Two genera.