Valve oblong-linear, with rounded ends, sometimes slightly constricted; axial area about one-half the width of the valve, dilated in the middle; striæ parallel in the middle, radiate at the ends, 15-16 in 10 µ. A punctum is usually found in the central nodule. L. 55-154 µ.
Blue clay. Occasional in fresh water.
Pl. [26], Fig. 8.
Decipientes Cl.
Valve lanceolate, with obtuse ends; axial area narrow; central area orbicular; striæ radiate in the middle and more distant.
NAVICULA SEMEN EHR.
Valve elliptic-lanceolate, with sub-rostrate, truncate apices; axial area narrow, sinuous; central area orbicular; terminal fissures small, hook-shaped; striæ robust, 7 or 8 in the middle, closer at the ends, indistinctly punctate or lineolate.
Blue clay. Not common.
Pl. [26], Fig. 11.
Cleve states that this form belongs to the post-glacial deposits and is found living only in the Hartz Mountains.