The 100 µm scale bar applies to figs. 3-5, 7a;
figs. 1, 2, 6 and 7b each have their own scale bar.
Fig. 1. Detail of the cortical shell of Didymocyrtis messanensis, with layered structure exposed and enchanced by (post-mortem) disolution. BSS 28B(VII/1550).
Fig. 2. Cortical shell of H. hexacanthum (see Pl. 33, fig. 3), showing closure of a pore by a thin siliceous film (analysed by EDAX) formed against the inner face of the first cortical shell. BSS 2B(II).
Figs. 3-5. Didymocyrtis ellipsoidis, with varying degrees of development of the cortical shell: in fig. 3, it is mostly lacking, in fig. 5 it is a thick, well developed layer surrounding (and mostly obscuring) the internal cavity. IOW 144(F) and 2x BSS 28B(II).
Figs. 6, 7. Heliodiscus sp. Fig. 6: medullary shell of showing excentrical internal structure and differences in pore-size. Fig. 7a: Medullary and cortical shell, broken and partially dissolved. Fig. 7b: Internal layering, in concentric rings, of the shell, laid bare by dissolution. BSS 28B(VIII/1092) and (VII/1603).