FIGURES 19–24. Planothidium sheathii SEM views. Figs 19, 20 in Planothidium sheathii a new monoraphid diatom species from rivers in California, USA

FIGURES 19–24. Planothidium sheathii SEM views. Figs 19, 20. External SV view. Fig. 21. Internal SV view with cavum. Figs 22, 23. External RV view. Note the more distant central shortened striae on secondary side (arrowheads). Fig. 24. Internal RV view. All figures from the type locality San Joaquin River, California, USA. All scale bars: 5 μm.