Pl. [23], Fig. 4.
(3) Transverse Striæ More Distant
GYROSIGMA ACUMINATUM (KUETZ.) CL.
Valve sigmoid, tapering to the sub-acute ends; raphe central; transverse and longitudinal striæ nearly equally distant, 17 or 18 in 10 µ (Per.).
Frustulia acuminata Kuetz.
Port Penn, Delaware River.
Pl. [23], Fig. 5.
GYROSIGMA STRIGILIS (WM. SM.) CL.
Valve sigmoid, with obtuse ends; raphe doubly sigmoid; axial area rather wide; transverse striæ, 13, and longitudinal, about 16 in 10 µ.
Long Island Sound. Not common.