The Diatomaceæ of Philadelphia and Vicinity

by Charles S. Boyer

GYROSIGMA PARKERI VAR. STAURONEIOIDES GRUN.

Valve lanceolate, slightly sigmoid, ends produced into beaks with sub-acute apices; raphe straight in the middle part; central nodule elliptical; transverse striæ, 21, and longitudinal, 24 in 10 µ (Per.).

An apparent stauros, variable in width, extends to the margin and, in consequence, the median transverse striæ are more evident. L. 75 µ.

Schuylkill River. Rather rare.

Pl. [23], Fig. 7.

GYROSIGMA SIMILE (GRUN.)

Valve slightly sigmoid, broad, with obtuse ends; raphe sigmoid, nearly central; transverse striæ, 15, longitudinal, 16-17 in 10 µ (Per.).

Pleurosigma simile Grun.

Gyrosigma balticum var. similis (Grun.) Cl.

Shark River, N. J.