Operculodinium tiara (Klumpp, 1953) Stover and Evitt, 1978

Originally Hystrichosphaeridium, subsequently Baltisphaeridium, thirdly Cordosphaeridium, fourthly Cleistosphaeridium, fifthly (and now) Operculodinium.

Holotype: Klumpp, 1953, pl.17, fig.8-9
Paratypes: Klumpp, 1953
Locus typicus: Kiel, N Germany
Stratum typicum: Eocene
Translation Klumpp, 1953: LPP

Original description: Klumpp, 1953, p. 391: Hystrichosphaeridium tiara
Diagnosis: A species of the genus Hystrichosphaeridium with the following special characteristics: the shell always has an oval, smooth-rimmed hole, which gives rise to the tiara-shape. The membrane consists of smooth, thin inner layer and a felty, thick outer layer. The processes are smooth, and stem from the inner layer, going through the felt-layer.
Description: Most striking is the thickness of the shell, the outer layer of which is 4 µm. This felt-layer slightly rises, in a cone-like fashion, along the smooth spines. The processes terminate in one or two tips. Near the oval opening the processes seem to be a little shorter.
Length 56 Ám, largest width 68 Ám, process length 14-18 Ám, length of opening 44 Ám.