Gonyaulacysta monacantha Deflandre, 1936b, p.176-177 ex Sarjeant, 1967b, p.252

NOW Apteodinium?. Originally Palaeoperidinium (name not validly published), subsequently Gonyaulacysta, thirdly Millioudodinium, fourthly Apteodinium, fifthly (and now) Apteodinium?.
The name Palaeoperidinium monacanthum was not validly published in Deflandre (1936b) since the generic name Palaeoperidinium was not validly published until 1967. Williams et al. (1998, p.253) accepted Sarjeant's (1967b) indirect reference to Deflandre (1935) as indication of a type (I.C.N. Article 40.3)

Holotype: Deflandre, 1935, pl.6, fig.1; Deflandre, 1936b, pl.5, fig.10; lost according to Jan du Chêne et al. (1986a, p.48)
Age: Late Cretaceous