Entomoneis alata

Valves in valve view at the valvar plane are linear-elliptic to linear lanceolate with slightly concave sides and apiculate apices. Highly arched bilobate keels dominate the view in girdle aspect. The keels are strongly torsioned so that only one lobe is in focus at one time. In complete frustules in girdle view, diagonally opposing lobes lie at approximately the same level of focus. Lobes are flattened in large specimens and more rounded in smaller specimens. Several girdle bands are present. The junction line between the valve and the keel, like the outer edge of the keel, is flattened in larger specimens and more rounded in smaller specimens. The junction line is marked by an irregular series of dark spots. In valve view these spots can be seen as thickened siliceous ribs that frame a series of prominent swellings along the junction line. The swellings are approximately equal in size. Striae on the valve face continue onto the keel. Areolae on the valve face are very fine and number 26-30 in 10 µm within a stria. Areolae on the keel are much more prominent and number 12-15 in 10 µm within a stria.