FIGURES 23–28 in Three new species of the diatom genus Halamphora (Bacillariophyta) from the prairie pothole lakes region of North Dakota, USA

FIGURES 23–28: SEM. Halamphora pertusa sp. nov. Fig. 23. External whole valve view. Fig. 24. Detail of external valve apex. Fig. 25. Detail of the external areolae structure, showing internal biseriate sieve plate (arrow). Fig. 26. Interior whole valve view. Fig. 27. Detail of interior valve center showing longitudinal band of silica (arrow). Fig. 28. Detail of valve interior showing biseriate striae.