Pl. [33], Fig. 3; Pl. [39], Fig. 1.
This is, probably, one of the most beautiful of the Nitzschiæ. It sometimes, according to De Toni, reaches a length of 520 µ.
Grunow states that his variety is found in the S. Bridgeton deposit. In a slide of Mœller labelled "Bridgeton, Maine," I find specimens identical in every respect with the Philadelphia form.
Lineares
NITZSCHIA LINEARIS (AG.) WM. SM.
Valve linear, slightly inflexed in the middle; keel excentric; keel puncta, 8-9 in 10 µ, the two median distant; striæ about 30 in 10 µ. Frustules in zone view narrowed toward the ends, truncate. L. 75 µ.
Very common in fresh water.
Pl. [32], Fig. 18. Fig. 20, Pl. [40], a transverse section of frustule.
Lanceolatæ
NITZSCHIA PALEA (KUETZ.) WM. SM.