Isabelidinium thomasii (Cookson and Eisenack, 1961) Lentin and Williams, 1977

Originally Deflandrea, subsequently (and now) Isabelidinium. See also Isabelia (combination illegitimate).

Holotype: Cookson and Eisenack, 1961, pl.11, fig.8
Paratype: Cookson and Eisenack, 1961
Locus typicus: Belfast No. 4 Bore, Victoria
Stratum typicum: Senonian

Original description: Cookson and Eisenacik, 1961, p.71-72: Deflandrea thomasii
Shell longer than broad, roughly oval with a median girdle with low borders which, sometimes, is only indicated at the lateral margins. The epitheca has a short, solid pointed horn which terminates in a minute hyaline prominance.
The antapex is variable in outline, it may be indented, obliquely truncate with a single short, pointed, lateral horn or broadly rounded. The shell membrane is 2 layered; the inner layer is thin and hyaline, the outer is formed of densely arranged minute granules or rods; it is from this layer that the apical horn is formed. In poorly preserved specimens the outer layer tends to be destroyed. The internal body is oval in outline and thin-walled; it appears to be absent from some specimens. The pylome is trapezoid in shape.
Dimensions: Type--length 108 Ám, breadth 82 Ám. Range--length 85-114 Ám, breadth 50-90 Ám.