Pl. [38], Fig. 9.
In Pl. [23], Fig. 6 represents a form more sigmoid.
GYROSIGMA SPENCERII VAR. NODIFERA GRUN.
Valve sigmoid, with obtuse ends; raphe central; central nodule obliquely elongated; transverse striæ, 17-18 in 10 µ, curved in the middle of the valve, longitudinal striæ, 22 in 10 µ. L. 150 µ.
Blue clay.
Pl. [23], Fig. 8.
GYROSIGMA PROLONGATUM (WM. SM.) CL.
Valve narrow, lanceolate, produced into beaks, curved in a contrary direction; raphe central; transverse striæ, 20-21 in 10 µ, longitudinal closer. L. 140 µ.
Along the coast, northward.
Pl. [38], Fig. 13.