From Fensome et al., 2019:
Amphidiadema rectangularis, (Cookson and Eisenack, 1962b, p.486, pl.1, figs.14–15) Lentin and Williams, 1976, p.61.
Holotype: Cookson and Eisenack, 1962b, pl.1, fig.14; Jan du Chêne et al., 1986a, pl.48, figs.14–15.
Originally Deflandrea, subsequently (and now) Amphidiadema.
Contrary to the belief of Stover and Evitt (1978, p.94), Gocht (1976, p.322) did not consider this species to be a taxonomic junior synonym of Triblastula (now Hystrichosphaeropsis) quasicribrata.
Age: late Turonian–middle Senonian.

Locus typicus: Perth Basin, Australia

---------------------------------------------------------------------------------------------------

Original description as Deflandrea rectangularis: [Cookson and Eisenack, 1962, p. 486]:

Description:
Shell elongate, flat, either nearly rectangular in outline or slightly narrowed above the limits of the capsule. Apex truncate to rounded, sometimes with a low central elevation. Antapex truncate to rounded or with slight indications of horns.
Tabulation, girdle and longitudinal furrow absent. Capsule circular to oval in outline, generally reaching the lateral margins of the shell. Wall of shell and capsule smooth, that of the capsule being thinner.

Dimensions:
Holotype: 120 µm long, 60 µm broad; capsule 4-x58 µm broad; pylome 24x26 µm.
Range: 100-130 µm long, 56-64 µm broad.