Palaeoperidinium sibiricum (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. This specific name, as Pentagonum sibiricum, was a nomen nudum in Vozzhennikova, 1963. According to Vozzhennikova, 1967, the specimens illustrated in Vozzhennikova, 1963 are specimens of Pentagonum sibiricum. However, in Vozzhennikova, 1963 the specimens illustrated in text-figs.17a-b are identified as Pentagonum conicoides Vozzhennikova.

Holotype: Vozzhennikova, 1967, pl.46, fig.2 (lost accoriding to Lentin and Vozzhennikova, 1990)
Lectotype: Lentin and Vozzhennikova, 1990, pl.7, fig.3, text-fig.34; designated by Lentin and Vozzhennikova, 1990
Locus typicus: Western Siberia, USSR
Stratum typicum: Paleocene
Translation Vozzhennikova, 1967: Lentin and Vozzhennikova, 1990

Original description: Vozzhennikova, 1967, p.106-107: Pentagonum sibiricum
Epitheca equal in size to the hypotheca or somewhat larger. Epitheca bell-shaped with a small apical horn which is bluntly rounded at the distal end. Hypotheca trapeziform with two short antapical horns. Transverse furrow equatorial, annulate, its ends laying very near to each other. Margin of the transverse furrow delimited by a narrow border. Longitudinal furrow extends over the hypotheca. Theca thin walled, its surface finely tuberculate, pale yellow in color. Pylome indistinct.
Size: Holotype, length 103 µm, width 94.5 µm, width of paracingulum 5-7 µm. Lectotype, length 116 µm, width 103 µm.