From Fensome et al., 2019:
Dinogymnium muticum (Vozzhennikova, 1967, p.46–47, pl.1, figs.6–7; pl.2, fig.9) Lentin and Williams, 1973, p.49. Emendation: Lentin and Vozzhennikova, 1990, p.19–20, as Dinogymnium muticum. Holotype: Vozzhennikova, 1967, pl.1, fig.6; Lentin and Vozzhennikova, 1990, text-fig.6a; lost according to Lentin and Vozzhennikova (1990, p.19). Neotype: Vozzhennikova, 1967, pl.1, fig.7; Lentin and Vozzhennikova, 1990, pl.2, figs.13–14; text-fig.6b; designated by Lentin and Vozzhennikova (1990, p.20). Originally Gymnodinium (Appendix B), subsequently (and now) Dinogymnium. Age: Senonian.

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Translation Vozzhennikova, 1967: Lentin and Vozzhennikova, 1990

Original description: Vozzhennikova, 1967, p. 46-47: Gymnodinium muticum
Theca biconical. Epitheca somewhat smaller than hypotheca. Epitheca short, broadly conical with one side straighter than the other giving the theca a somewhat slanting appearance. The hypotheca resembles a bluntly truncated cone. Traverse furrow deep, annulate. Longitudinal furrow barely distinguishable but apparently slit-like. Thecal surface granular.

Emended description: Lentin and Vozzhennikova, 1990, p. 20
Cyst shape elongate, epicyst long with conical, pointed apex; hypocyst shorter than epicyst, broadly conical with one site shorter producing asymmetry; autophragm minutely granulose with longitudinal ridges running the entire length of the cyst interrupted only by the paracingulum; archeopyle formed by two arcuate sutures approximately 5 µm long, which result in the loss of the pointed apex; paracingulum teep, dividing the cyst into two unequal portions, the epicyst being somewhat longer than the hypocyst; parasulcus inticated by a deep longitudinal groove which is difficult to distinguish except at the slightly offset paracingular margin.
Size: Neotype, 48 µm long, 35 µm wide, paracingulum 2-3 µm wide; range, 47-57 µm long, 32-35 µm wide.