Bolma Risso, 1826. Species here placed in Bolma are similar in having a turbinate shell; one or, in most species, two angulations on the last whorl (and one on spire whorls) that bear nodules or spines on most species; a simple columellar callus which, in mature shells of most species, spreads over much of the base adjacent to the columella, and is coloured yellow or orange in some species. The operculum is simple, markedly convex, and smooth or with a granular, in some species depressed, central area. The position of angulations on whorls, length of spines, and details of fine nodular ornament and opercular sculpture, features that have been used to define several genera or subgenera, seem to us to be specific characters within this group and we propose to place all species in the genus Bolma, recognising as a separate subgenus only Senobolma Okutani, 1964.
Two species groups can conveniently be recognised within Bolma s.s. One, the ''Bolma rugosa group" is composed of species with generally rather solid, larger shells, usually with distinct, irregular axial folds dorsally and an oval, often coloured operculum. The other group, the "Bolma guttata group" is composed of species with generally smaller shells of lighter build and usually with a white, circular operculum and regular gemmate sculpture. Some species share some features of both groups and consequently the groups are not considered to be of subgeneric status.