The genus is divided into two groups, one in which the costæ alternate with double rows of puncta, as in E. turgida, and the other in which the rows of puncta are more than two.
The endochrome usually consists of a band lying along the ventral zone and extending in two flaps on the valves.
EPITHEMIA TURGIDA (EHR.) KUETZ.
Valve arcuate, with ends subcapitate; costæ radiate, 4 in 10 µ, alternating with double rows of puncta. Median nodule central, the raphe curved toward the ventral edge which it closely follows.
Parasitic on algæ. Very common in fresh water, especially in ponds. In the figure the valve is asymmetrical with respect to the transverse axis, an unusual condition.
Pl. [31], Fig. 14.
EPITHEMIA ARGUS KUETZ.
Valve with dorsal margin convex, and ventral margin nearly straight; ends rounded, constricted; costæ robust, alternating with more than two rows of puncta; zone view rectangular, the thickened ends of the costæ forming large nodules in a row along the edge of the valve next to the connecting zone.
Cystopleura argus (Ehr.) Kunze.
Common in fresh water.