The Diatomaceæ of Philadelphia and Vicinity

by Charles S. Boyer

(b) COSCINODISCINÆ

1. Cyclotella.—Valve with two concentric divisions of different structure, one a wide border and the other a central surface.

2. Coscinodiscus.—Valve areolate or punctate, with a narrow border of the same structure.

Cyclotella Kuetz. (1833)

(cyclos, a circle)

Frustules single or geminate, cylindrical, short, in zone view rectangular or with undulating sides. Valve usually with smooth or punctate striæ, centre sometimes bullose, smooth, or with granules scattered or radiating.

Chromatophores numerous along the valves (Pfitzer).

CYCLOTELLA STRIATA (KUETZ.) GRUN.

Valve 30-80 µ in diam., with coarse striæ, 7-12 in 10 µ, centre coarsely punctate and bullose.

Coscinodiscus striatus Kuetz.