Cyclonephelium crassimarginatum Cookson and Eisenack, 1974

Holotype: Cookson and Eisenack, 1974, pl.28, fig.3
Age: Middle Cretaceous

Original diagnosis: Cookson and Eisenack, 1974, p.74-75
A Cyclonephelium-species with more or less thickened margin, and with fairly sturdy, radially directed, but irregularly developed and arranged supports, which support a more or less broad membrane with a continuous and smooth margin.As in the case of the Cyclonephelium-species, the base of the supports still lies on the flat sides of the shell in the vicinity of the margin, so that the supports come from both sides; accordingly the membrane is double, a phenomenon which is, however, only difficult to recognize. The surface of the shell is more or less distinctly granular.
Dimensions and occurrence: Type about 94 Ám broad. The breadth of the remaining specimens lies between about 94 and 114 Ám.
The specimens stem from the Gingin Brook bore from a region comprised between 404-414 ft. (Figure 1 ) and from the Balcatta bore, 240 ft.

Remarks: Cookson and Eisenack, 1974, p.75
The structure of the membrane is best recognized in case of injuries; in Figure 1, the specimen is slightly laterally compressed.