The bulla was a circular gold locket containing a charm of some kind against evil.'
In connexion with the large size of the ears is the excessive inflation of the auditory bulla of the skull.
Actaeon is prosobranchiate, the visceral commissure is twisted in Actaeon and Chilina, and even slightly still in Bulla and Scaphander; in Actaeon and Limacina the osphradium is to the left, innervated by the supra-intestinal ganglion.
The Thecosomatous Pteropoda are allied to Bulla, the Gymnosomatous forms to Aplysia.
It is one of the more typical Opisthobranchs, that is to say, it belongs to the section Tectibranchia, but other members of the suborder, namely, Bulla and Actaeon (figs.