Cleistosphaeridium tiara, (Klumpp, 1953), Davey et al., 1969

Now Operculodinium. Originally Hystrichosphaeridium, subsequently Baltisphaeridium, thirdly Cordosphaeridium, fourthly Cleistosphaeridium, fifthly (and now) Operculodinium.
This combination was not validly published in Davey et al., 1966, since these authors did not fully reference the basionym.

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

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Original description as Hystrichosphaeridium tiara: [Klumpp, 1953, p. 391]: (Translation: LPP):

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 µm, largest width 68 µm, process length 14-18 µm, length of opening 44 µm.