From Williams et al., 2017:

[Pentagonium, Snopková and Samuel, 1982, p. 132
Acritarch genus.
Name illegitimate — senior homonym: Pentagonium Schauer, 1843.

Type species: Pentagonium obidum, Snopková and Samuel, 1982, (pl.48, figs.1–3; pl.49, figs.1–2; pl.50, fig.1)]