FIGURES 7–13 in External ultrastructure of Progonoia diatreta sp. nov. (Bacillariophyta, Scoliotropidaceae) differs from P. musca and P. intercedens comb. nov.

FIGURES 7–13. Progonoia intercedens, LM (Figs 7–10 DIC) and external SEM (Figs 11–13). 7, 8. Oblique frustule at two focal planes. 9. Valve. 10. Frustule in girdle view, showing the striae on the copulae. 11. Valve, external view. 12. Detail of areolae showing contrasting structure of longitudinal rows: a hymen near the surface in the middle rows (arrowhead), probably unbroken in life, and the deeper pits of the inner and marginal areolae (arrows). Notice also the small pores with structure similar to the middle rows. 13. Detail of marginal areolae, showing the deeper membranes with small marginal perforations (arrow). Scale bars: Figs 7–10 = 10 μm, Fig. 11 = 5 μm, Figs 12, 13 = 1 μm.