FIGURES 25–29. Planothidium sheathii SEM views. Fig. 25 in Planothidium sheathii a new monoraphid diatom species from rivers in California, USA

FIGURES 25–29. Planothidium sheathii SEM views. Fig. 25. Internal view of RV areolae. Figs 26, 27. Detail of cavum aperture. Note the boarders of the aperture attached to neighbor virgae. Fig. 28. External view of SV periphery and mantle. Striae 5–6 seriate, interrupted at valve mantle junction. Note the separated groups of 8–13 rounded areolae, bordered by 2 elongated areolae on mantle in oblique position to each areola group (arrows). Fig. 29. External view of RV periphery and mantle. Striae 5–6 seriate, interrupted at valve mantle junction. Note the separated groups of 7 rounded areolae on mantle (arrows). All figures from the type locality San Joaquin River, California, USA. All scale bars: 1 μm.