The Diatomaceæ of Philadelphia and Vicinity

by Charles S. Boyer

Frustule sigmoid, truncate at the ends; valve linear, with sub-acute apices and nearly central keel; keel with 5-6 puncta in 10 µ; striæ obscure, about 25 to 28 (?) in 10 µ. Length variable, up to 490 µ.

As the valve is usually seen when the keel is on the margin, the outline (reduced one-third, shown to the left of the figure) is, as a rule, sigmoid.

Delaware Bay.

Pl. [33], Fig. 7.

NITZSCHIA VERMICULARIS (KUETZ.) HANTZSCH

Valve linear, sigmoid, attenuated toward the obtuse ends; keel puncta, 9 in 10 µ, quite distinct; striæ very fine. L. 105 µ.

Fresh-water pools.

Pl. [32], Fig. 24; Pl. [33], Fig. 9.

SIGMATA

NITZSCHIA SIGMA (KUETZ.) WM. SM.