From Williams et al., 2017:

[Opaeopsomus, Pocock, 1972, p. 96

tax. jr. synonym of Ellipsoidictyum Klement, 1960, according to Stover and Evitt, 1978 & Dapcodinium Evitt, 1961, according to Dörhöfer and Davies, 1980 — however, Lentin and Williams (1993, p.465) retained Opaeopsomus.
tax. jr. synonym of Valvaeodinium Morgenroth, 1970, according to Below, 1987. Lentin and Williams, 1993, retained Opaeopsomus, with the recommendation that the name be restricted to the holotype of O. wapellensis.

Type species: Opaeopsomus wapellensis, Pocock, 1972 (pl.24, fig.14)]

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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.