Palaeocystodinium? hyperxanthum (Vozzhennikova, 1963, p.185, fig.20) Vozzhennikova, 1967, p.152. Emendation: Lentin and Vozzhennikova, 1990, p.60, as Palaeocystodinium? hyperxanthum.

Originally Cystodiniopsis, subsequently Palaeocystodinium, thirdly (and now) Palaeocystodinium?. Stover and Evitt, 1978 considered this to be a "provisionally accepted species" of Palaeocystodinium.

Holotype: Vozzhennikova, 1963, fig.20 (lost according to Lentin and Vozzhennikova, 1990)
Lectotype: Lentin and Vozzhennikova, 1990, pl.7, fig.7, text-fig.31; designated by Lentin and Vozzhennikova, 1990, p.60
Locus typicus: Western Siberia, USSR
Stratum typicum: Palaeocene
Translation Vozzhennikova, 1967: Lentin and Vozzhennikova, 1990

Original description: Vozzhennikova, 1963, p.185: Cystodiniopsis hyperxantha
Theca with the middle part closely applied to the elliptical internal body and with the anterior and posterior ends drawn out into long processes truncated at the distal end. Theca and internal body thin walled, their surface is smooth or finely dotted, colored deeply or pale yellow. Pylome absent.

Emended description: Lentin and Vozzhennikova, 1990, p.60
Cyst shape elongate ellipsoidal, with single slender, pointed apical and antapical horns at each pole, usually found in lateral orientation; autophragm thin, minutely granulose, normally dark brown in color.
Paratabulation indicated by archeopyle parasutures only; peridinioid.
Archeopyle attenuated hexa type, intercalary 2a, operculum apparently free but seldom removed.
Paracingulum is not indicatet; parasulcus is not indicated.
Size: Holotype, length 161µm, width 38µm; Lectotype, length 126µm (apical horn broken off), width 37µm. Range, length 150 - 165µm, width 35 - 40µm.