Hannaea inaequidentata, an initial frustule, external view, SEM 79 complete initial frustule, note its rounded, cylinder-like, twisted outline 80 middle detail of Fig. 79, showing central area, sternum not developed (i.e. striae continue across valve surface, also see 81, 83, arrow), longitudinal perizonium wholly covering valve surface, no transverse perizonium bands (also see Figs 85–106) 81 detail of Fig. 79 showing sternum not developed (arrow) 82 apex detail of Fig. 79 showing two girdle bands for this initial frustule, sternum not developed. 83, 84 details of Fig. 79 showing two disc-shaped incunabular scales with cerebral-cortex-like surfaces (83 curved arrow; 84 arrow). Scale bars: 10 μm (79), 2 μm (80–84).