The resemblance between Eunotia and Epithemia is noticeable. In both, the epiphytic character of the valve is seen in the shape of the frustule which is arched, and, in the free forms, is adherent at the ends only. In Epithemia, the median is more evident than the terminal nodules. In Eunotia, there is no median nodule, but the end nodules, in some species, are quite evident, and a tendency is shown to produce a very short raphe. The arrangement of puncta in valve view is similar in both genera.
Section 1. Himantidium
EUNOTIA MAJOR (WM. SM.) RAB.
Valve arcuate, linear, subcapitate, recurved. Striæ punctate, 12 in 10 µ L. 90-190 µ.
Common in fresh water.
Pl. [13], Figs. 1 and 2.
EUNOTIA GRACILIS (EHR.) RAB.
Valve with sides parallel; apices slightly capitate and revolute; striæ, 10 in 10 µ. The striæ on the connective membrane more delicate than in E. major. Intermediate forms occur.
Common in fresh water.
Pl. [13], Fig. 3. Fig. 4 is indeterminate.