From Fensome et al., 2019:

"Omanodinium", Bradford, 1975, p.3070.
Taxonomic senior synonym: Selenopemphix, according to Bradford and Wall (1984, p.49) and Head (1993, p.32). Lentin and Williams (1981, p.202) did not agree with Harland and Reid in Harland et al. (1980, p.223) that Omanodinium and the two included species, Omanodinium alticinctum and Omanodinium tholus, are not validly published names because they lack Latin diagnoses. As no living forms were observed, Lentin and Williams (1981) agreed with Bradford (1975), who clearly stated that he considered cysts of unknown origin in unconsolidated sediments to be fossils.
Type: Bradford, 1975, figs.23–26, as Omanodinium alticinctum.

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Original description: [Bradford, 1975]:

Diagnosis:
Proximate cysts, pentagonal in shape dorsoventrally, usually circular in polar view. Epitract and hypotract of similar size, divided by a broad cingulum of varying width. Epitract dome-shaped, with or without an apical horn. Hypotract very variable in shape, most often with concave sides- may possess one or two antapical horns.
Anterior intercalary archeopyle.
Tabulation absent; sulcus usually present.