Asymmetrical biraphid - Valves are linear-lanceolate with subcapitate ends. The ventral side of the central part of the valve is expanded. A stigma is present on the dorsal side of the central area. Striae are comprised of two rows of areolae (biseriate).
Asymmetrical biraphid - Valves are linear-lanceolate with subcapitate ends. The ventral side of the central valve is expanded. A stigma is present on central nodule. Striae are comprised of one row of areolae (uniseriate).
Symmetrical biraphid - Valves are broadly lanceolate with apices protracted to broadly rounded. The raphe is lateral and undulate. Within a stria, the marginal areolae are large and more coarsely arranged. The middle valve has areolae comparatively smaller and rounded. Central area has large, round isolated puncta. The smallest striae at the apices are multiseriate throughout their length.
Asymmetrical biraphid - Valves are clavate, or club-shaped with rounded ends. In girdle view, frustules are distinctly arched. In valve view, the arch prevents resolution of the entire valve face at one level of focus. Pseudoseptum present at each pole. One valve possesses a fully developed raphe system, the other valve possesses short raphe slits.
Asymmetrical biraphid - Valves are linear-lanceolate and heterovalvar. The valves are narrow, 3-6 µm wide.The axial area is narrow on both the raphe and reduced raphe valves. The central area is small and ovate. Proximal raphe ends are relatively close together on the raphe valve. The apices are protracted, especially in larger specimens. The striae are lineate, rather than distinctly punctate.
Asymmetrical biraphid - Valves are linear to narrowly clavate, with acute apices. The proximal raphe ends are broadly spaced from one another and positioned within a panduriform central area. Valves range from 80 to 25 µm in length and 6-9 µm in width. Areolae are distinctly lineate and number 11–13 in 10 μm.
Epithemioid - Valves linear, with apices bent towards the ventral margin. The center is deflected slightly towards the dorsal margin and notched. The raphe is positioned in a canal. Costae are prominent, and extend across the valve face.
Epithemioid - Valves are lunate, with strongly convex dorsal margins that are often slightly notched in the middle.The ventral margin is slightly concave to straight. In girdle view, frustules are broadly lanceolate to elliptical. Apices are slightly bent ventrally, or protracted and acutely rounded. The raphe is located on dorsal margin and is difficult to distinguish. Transapical costae may be slightly radiate.
Rhopalodia gibberula var. musculus
Epithemioid - Valves semi-elliptical, strongly convex along the dorsal margin, concave along the ventral margin, tapering to narrowly rounded ends. Costae distinct, numbering 3-5 in 10 µm. Striae are in rows of 2-4 between the costae.
Monoraphid - Valves are linear or linear-elliptic with rounded ends. The raphe valve has a linear axial area that gradually widens into a small or almost indistinct central area. The rapheless valve has a narrow, linear axial area and no distinct central area. Striae are uniseriate and slightly radiate.
Monoraphid - Valves are linear-elliptical or elliptical with slightly drawn-out ends. The striae are slightly radiate throughout both valves and biseriate. The axial area is narrow. The central area is small, or absent. If present, it may be asymmetrical on the rapheless valve.
Monoraphid - Valves are linear or linear-elliptical with rounded ends, 3.5-4.5 µm wide, 13-18.5 µm long. Raphe valve has a large transverse elliptical central area that almost reaches the valve margins. Terminal raphe fissures are absent. Rapheless valve has a narrowly rhomboid axial area and no distinct central area. Striae are uniseriate, slightly radiate, and number 32-36 in 10 µm.
Monoraphid - Valves are linear to linear-elliptical or linear-lanceolate with rounded ends. The terminal raphe fissures are not distinct. The striae are uniseriate, with 4-5 areolae per stria, and slightly radiate throughout both valves.