The Diatomaceæ of Philadelphia and Vicinity

by Charles S. Boyer

COCCONEIS PLACENTULA EHR.

Valve elliptical; upper valve with a linear or lanceolate axial area, and punctate striæ in transverse and radiating rows, the puncta at equal distances; the lower valve with a lanceolate axial area, radiating rows of puncta, and a wide border of finely punctate, radiating striæ, separated from the central part of the valve by a narrow hyaline zone.

Common in salt, brackish and fresh water.

Pl. [16], Figs. 19 and 20.

COCCONEIS PLACENTULA VAR. LINEATA (EHR.) V. H.

As in the type, except that the upper valve has the puncta arranged in zig-zag, giving the appearance of sinuous, longitudinal lines.

Common along the coast.

Pl. [16], Fig. 29.

C. pediculus and C. placentula are the only species I have found in fresh water. Cleve states that the former occurs also in brackish water.

The following are among the species placed by Cleve in a new genus, Eucocconeis, distinguished by the absence of a loculiferous rim.