FIGURES 27–29 in External ultrastructure of Progonoia diatreta sp. nov. (Bacillariophyta, Scoliotropidaceae) differs from P. musca and P. intercedens comb. nov.

FIGURES 27–29. Progonoia diatreta, sp. nov., internal SEM. 27. General view of valve. 28. Detail of apex showing terminal raphe ending and internal aspect of alveoli, with partial transverse walls and a series of small pores around the inner edge of one, the outer edge of the other, and the apical end of the last alveolus (arrow). Some of the pores of the external surface can be seen where the inner membrane has broken away (arrowhead). 29. Detail of central area showing the double helictoglossa (arrow) and the partial transverse walls extending into each alveolus from the longitudinal wall (arrowhead). Scale bars: Fig. 27 = 10 μm, Figs 28, 29 = 2 μm.