Shell conical; valves strongly and irregularly ribbed; interstices delicately striated transversely; colour purple.
B. spinosus. The spiny Balanus.
Either has no support or a membranous one; armed with spines exteriorly.
4. Acasta. Three species.
Found in sponge, from which, when detached, it cannot stand erect on account of the convexity of the base.
Shell oval, sub-conic, shaped like a Patella, with six lateral unequal valves slightly connected; operculum with four valves.
Acasta Montagui.
A. glans.
A. sulcata.
A. Montagui. Montague’s Acasta.