Phalium, common name the bonnet shells, is a genus of large sea snails, marine gastropod molluscs in the subfamily Phaliinae of the family Cassidae, the helmet shells, bonnet shells and their allies.

[1] Abbott (1968) held a very comprehensive concept of the genus Phalium, to include all the species of the subfamily Phaliinae except those included in Casmaria H.& A. Adams, 1853.

Current authors (Alf, 1997; Beu, 2008) would include in Phalium only those species which have varixes all along the spire and have spines around the outer edge of the terminal varix as in Casmaria.

Species with predominantly spiral sculpture and with only a terminal varix without spines are currently classified in Semicassis Mörch, 1852 but often cited under Phalium.

[1] According to the World Register of Marine Species (WoRMS), the following species with valid names are included within the genus Phalium :[2]