FIGURES 38–42 in Surirella subrotunda sp. nov. and Surirella parahelvetica sp. nov., two new diatom (Bacillariophyta) species from Lake Prespa, Macedonia

FIGURES 38–42: Surirella parahelvetica (SEM). Figs 38, 41. External views. Fig. 41. Short conic spines along inner side of keel (white arrow), spines on alar canals (black arrow). Keel with silica ridges following raphe and a random pattern of silica thickening on the keel. Figs 39, 40, 42. Internal views. Fig. 42. terminal raphe fissures with simple pores, not deflected and areolae with ringed domes. Scale bars in Figs 38–40 = 10 µm; Fig. 41 = 5 µm; Fig. 42 = 2 µm.