From Fensome et al., 2019:
Pentadinium membranaceum (Eisenack, 1965b, p.151, pl.14, fig.4; pl.15, fig.6; text-fig.1) Stover and Evitt, 1978, p.180.
Holotype: Eisenack, 1965b, pl.14, fig.4; text-fig.1; Jan du Chêne et al., 1986a, pl.80, figs.4–7. Originally Planinosphaeridium, subsequently (and now) Pentadinium. Taxonomic junior synonym: Ataxiodinium choane according to Dale (1976, p.45; footnote to table II) — however, Edwards and Andrle (1992, p.265) retained Ataxiodinium choane. Age: Late Eocene–Early Oligocene.

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Locus typicus: NW Germany
Stratum typicum: Late Eocene-Early Oligocene

Original diagnosis: Eisenack, 1965, p.151: Planinosphaeridium membranaceum
Central body nearly sphaeroidal, surrounded by an irregular membrane. The shell is fine to coarsely granulate or vermiculate. Type consists of a large, trapezoidal pylome with rounded corners.

Dimensions:
Type: central body 54x56 µm, allover 70-82 µm, pylome 30x32 µm.