Frustulia rexii

Valves rhomboid with a very slight constriction near rounded poles; 68.0–111.0 μm long, 17.5–21.0 μm wide. Striae with density of 26–28 in 10 μm at valve centre, 28 in 10 μm at valve ends. Striae mostly parallel but slightly convergent and sometimes wavy at apices (Figs 42 and 44). Externally, areolae lanceolate or round (Figs 51 and 52) with the most rounded areolae being located near valve centre (Fig. 52). Adjacent to external central area, areolae can be slightly expanded (Figs. 45, 46, and 52). Internally, areolar openings round (Figs 54 and 55). Areolae extend around apices, but striae greatly reduced (Fig. 51). Longitudinal striae parallel over majority of valve but become slightly wavy at valve centre (Figs 42 and 45). External central area possessing an irregular grouping of small poroids of varying number (Figs 44, 47, and 52). Rows of areolae adjacent to either side of raphe terminate before distal raphe ending (Fig. 51). Internal longitudinal ribs robust, widen significantly but smoothly at central area before constricting at central nodule (Figs 53 and 55). Longitudinal ribs widen very abruptly near apices, then terminate bluntly at helictoglossa (Figs 42, 45, and 53). Longitudinal ribs fuse with the linear helictoglossa to form a wide and prominent porte-crayon structure (Fig. 54). External proximal raphe ends expanded into shallow crescent-moon shapes (Figs 51 and 52).

• Author
  Graeff and Kociolek in Graeff et al. 2012
• Length Range
  68-111 µm
• Width
  17.5-21.0 µm
• Striae in 10µm
  26–28 in the center, 28 at the ends