From Fensome et al., 2019:

Opaeopsomus, Pocock, 1972, p.96.
Taxonomic senior synonyms: Ellipsoidictyum, according to Stover and Evitt (1978, p.69); Dapcodinium, according to Dörhöfer and Davies (1980, p.23); Valvaeodinium, according to Below (1987b, p.64) -- however, Lentin and Williams (1993, p.465) retained Opaeopsomus. Pocock (1972, p.96) cited this genus as "Opaeopsomus Evitt n.gen.". Lentin and Williams (1993, p.465) recommended that this name be restricted
to the "type species".
Type: Pocock, 1972, pl.24, fig.14, as Opaeopsomus wapellensis.

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Original description: [Pocock, 1972]:

Description:
Vesicle ellipsoidal to spherical, usually relatively small.
Archeopyle apical.
Wall bears a series of ridges or septa which may only reflect tabulation, or may be supplemented by additional ridges or septa which may result in the formation of a coarse or fine reticulum. A thin membrane, supported by the ridges or septa, may or may not be developed.

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Stover and Evitt, 1978, p. 69:

Comment:
Opaeopsomus is probably congeneric with Ellipsoidictyum.