From Fensome et al., 2019:
Cleistosphaeridium tiara ssp. tiara Autonym. Holotype: Klumpp, 1953, pl.17, figs.8–9. Now redundant. NIA

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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.

Dimensions:
Length 56 µm, largest width 68 µm, process length 14-18 µm, length of opening 44 µm.