Eunotia lewisii

Valves are dorsi-ventral, elongate, with offset broadly rounded and slightly rostrate apices (Figs. 1–5). The ventral margin is straight and parallel with the dorsal margin over most of the valve, then extends outward slightly at the point where the raphe begins and where the apices start to constrict along the dorsal margin. The extended section is more noticeable on longer valves. The ventral valve margin is thickened, often forming a small continuous ridge (Figs. 8–10). A row of small spines can be found on the costae along the dorsal margin (Fig. 11), but these can be reduced or even absent on some specimens. The striae are evenly spaced and parallel over most of the valve; at the apices the striae are denser and radiate away from the terminal hyaline area onto the mantle (Figs. 8–10 and 12). Areolae are small, circular, closely spaced and not occluded on either the external nor internal surfaces (Figs. 8–13). The proximal end of the raphe commences about midway down the mantle, runs relatively straight and parallel to both margins, then curves up onto the valve face about 3 µm from the apex (Figs. 8–10). The distal raphe fissure terminates as a small pore about 1/4 the way across the valve face (Fig. 8). The raphe often interrupts the ridge on the ventral margin (Fig. 8). Internally where the distal end of the raphe terminates, a large, solid, thickening extends from the ventral mantle, across the valve face and terminates close to or at the dorsal margin (Figs. 6, 7, and 11–13). The thickening is usually smooth and hyaline. The distal end of the raphe curves up onto the proximal side of the thickened structure and terminates midway across the valve face as a small swollen helictoglossa (Figs. 12–13). The lower margin of the mantle is thickened, especially around the apices (Figs. 12 and 13). A single well-developed rimoportula, positioned parallel with the apical axis, is present near the base of the mantle at the very apex (Figs. 11 and 13). Valves ranged in size from 44–112 µm long x 5.5–6.5 µm wide with a striae density of 20–25/ 10 µm.

• Author
  Siver and Hamilton 2009
• Length Range
  44-112 µm
• Width
  5.5-6.5 µm
• Striae in 10µm
  20-25