The Diatomaceæ of Philadelphia and Vicinity

by Charles S. Boyer

Pl. [22], Fig. 8.

(3) Oblique Striæ 60 Degrees

PLEUROSIGMA ANGULATUM (QUEKETT) CL.

Valve rhomboidal, with sub-rostrate or produced ends; central nodule rhomboidal; raphe central; transverse and oblique striæ at an angle of 60 degrees, equidistant, 18-22 in 10 µ.

Navicula angulata Quekett.

Along the coast.

Pl. [22], Fig. 3.

PLEUROSIGMA STRIGOSUM WM. SM.

Valve lanceolate, with sub-acute, somewhat revolute, apices; oblique striæ at an angle of about 60 degrees, otherwise as in angulatum.

Along the coast. Not common.