Palaeoperidinium marginatum (Vozzhennikova, 1967) Lentin and Williams, 1976

Originally Pentagonum, subsequently Palaeoperidinium.
Tax. jr. synonym of Palaeoperidinium pyrophorum (Ehrenberg, 1838) Sarjeant, 1967, according to Lentin and Vozzhennikova, 1990.
Holotype: Vozzhennikova, 1967, pl.46, fig.6; Lentin and Vozzhennikova, 1990, pl.7, fig.6; text-fig.33; (lost according to Lentin and Vozzhennikova, 1990)
Lectotype: none available according to Lentin and Vozzhennikova, 1990
Locus typicus: Western Siberia, USSR
Stratum typicum: Palaeocene
Translation Vozzhennikova, 1967: Lentin and Vozzhennikova, 1990

Original description: Vozzhennikova, 1967, p.107: Pentagonum marginatum
Theca strongly compressed in a torso- ventral direction; epitheca slightly larger than hypotheca, triangular in outline with straight or slightly curved sites ant with a short, blunt-ended apical horn. Hypotheca trapeziform with 2 short, widely separated antapical horns. Transverse furrow equatorial, annual, its borders having a narrow rim. Longitudinal furrow extends over the hypotheca and apparently reaches the antapex. One, or less frequently two, sides of the theca have a border striated with transverse parallel lines. The border increases in width towards the transverse furrow. Theca thin walled, smooth, or finely punctuate, pale yellow in color.
Size: Holotype, length 124 µm, width 99 µm, width of transverse furrow about 6 or 7 µm. Range, length 120-127 µm, width 92-99 µm.