Cleistosphaeridium williamsii, (Boltenhagen, 1977, p.41-42, pl.2, figs.6-7), Islam, 1993, p.87.

Originally Polysphaeridium, subsequently Cleistosphaeridium, thirdly (and now) Impletosphaeridium.

Holotype: Boltenhagen, 1977, pl.2, fig.6; Fauconnier and Masure, 2004, pl.50, fig.6.
Age: Cenomanian-Early Turonian.