Pentagonum sibiricum Vozzhennikova, 1967

Originally Pentagonum (generic name illegitimate), subsequently Palaeoperidinium.
Taxonomic senior synonym: Peridinium (now Palaeoperidinium) pyrophorum, according to Lentin and Vozzhennikova (1990, p.61).
Following I.C.N. Article 55.1, the specific name Pentagonum sibiricum was validly published in Vozzhennikova (1967) even though the generic name Pentagonum is illegitimate. As indicated by Vozzhennikova (1963, p.183) and confirmed by Vozzhennikova (1967, p.106), the specimens illustrated in Vozzhennikova (1963, text-figs.17a–b) are specimens of Pentagonum sibiricum, even though the caption identifies them as Pentagonum conicoides. The name Pentagonum sibiricum was not validly published in Vozzhennikova (1963) since no holotype was designated.

Holotype: Vozzhennikova, 1967, pl.46, fig.2 lost, according to Lentin and Vozzhennikova, 1990
Lectotype: Lentin and Vozzhennikova, 1990, pl.7, fig.3; textfig.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
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 Ám, width 94.5 Ám, width of paracingulum 5-7 Ám.