From Fensome et al., 2019:
Amphidiadema? similis, Marheinecke, 1992, p.80–81, pl.16, figs.5–7; text-fig.14.
Holotype: Marheinecke, 1992, pl.16, fig.7.
Questionable assignment: Marheinecke (1992, p.80).
Contrary to the opinion of Lentin and Williams (1993, p.24), Williams et al. (1998, p.39) considered this name to be validly published.
Age: early–late Maastrichtian.

Locus typicus: Hemmoor, Lower Saxony, Germany

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Original description: [Marheinecke, 1992, p. 80]: (Translation: LPP):

Description:
Cyst bicavate ovaloidal. Endoblast subsphaeroidal, transparent with slightly granulate surface. Periblast transparent, weakly granulate or smooth. Apex and antapex rounded and in size and shape equally developed.
Archaopyle uncertain.
Cingulum and sulcus not indicated.

Affinities:
?Amphidiadema similis shows simularities to Xenikoon australis. These differ in shape of the antapical pericoel.