FIGURES 17–21. Stauroneis schinzii var. argentina Frenguelli. Specimens from type population. SEM. Fig. 17 in Revision Of The Type Materials Of Stauroneis Schinzii Var. Argentina Frenguelli And S. Schinzii Var. Maxima Frenguelli (Bacillariophyceae)

FIGURES 17–21. Stauroneis schinzii var. argentina Frenguelli. Specimens from type population. SEM. Fig. 17. Broken valve in external view. Fig.18. Broken valve in internal view. Fig. 19. Detail of external valve end showing distal raphe fissure. Note one row of poroids on each girdle band (arrows). Fig. 20. Detail of external valve face; note the transapical elongated areolae. Fig. 21. Detail of internal valve center showing proximal raphe ends. Scale bars: 10 µm (Figs 17–18); 2 µm (Figs 19–21).