Encyonema yellowstonianum

Valves are strongly dorsi-ventral. The dorsal margin is broadly arched, while the ventral margin is slightly expanded. Valves are 39-75 μm long by 17-23 μm wide, as reported by Krammer (1997). The valve apices are rounded. The axial area is relatively broad in the central part, narrowing at the valve ends. The raphe branches are lateral and have a slight arch towards the ventral margin. Each raphe branch is positioned nearly centrally within the axial area. Proximal raphe ends are slightly expanded and dorsally deflected. Distal raphe ends curve slightly to the dorsal margin, but are deflected ventrally near the valve apices. The dorsal striae are divergent. The rows of external dorsal areolae closest to the central area are oval, to irregular and become lineolate. Central dorsal striae 10-11 in 10 μm and distal striae 5 in 5 μm. Central ventral striae 7-8 in 10 μm, and distal striae 6 in 5 μm. The density of areolae within a central, dorsal stria is 8 in 5 μm. The striae continue on the dorsal valve margin.