Operculodinium microtriainum (Klumpp, 1953) Islam, 1983; Emendation: Sarjeant, 1981, p.110–112, as Achomosphaera microtriaina.

Originally Hystrichosphaeridium, subsequently Cordosphaeridium, thirdly Cordosphaeridium?, fourthly Polysphaeridium, fifthly Achomosphaera, sixthly (and now) Operculodinium.
Taxonomic junior synonym: Operculodinium paucispinosum, according to Jain and Garg (1991, p.80).

Holotype: Klumpp, 1953, pl.17, fig.6-7; Sarjeant, 1981, pl.2, fig.1-2, text-fig.2
Paratypes: Klumpp, 1953
Locus typicus; Woehrden, Holstein, Germany
Stratum typicum: Late Eocene
Translation Klumpp, 1953: LPP

Original description: Klumpp, 1953, p. 390: Hystrichosphaeridium microtriaina
Diagnosis: A species of the genus Hystrichosphaeridium with the following special characteristics: the membrane of the shell is bi-layered. The numerous processes are formed by the outer layer and terminate in three small hooks.
Description: The shell appears relatively delicate, the outer layer is irregularly sculptured, the netlike ridges rising along the hollow processes.
Diameter: 48 Ám; process length: 24-26 Ám.
Variation: Diameter 44-100 Ám, processes12-36 Ám.