The Diatomaceæ of Philadelphia and Vicinity

by Charles S. Boyer

COSCINODISCUS ARGUS EHR.

Markings angular with central dots, increasing from the centre toward the border, where they are smaller.

Blue clay.

Pl. [3], Fig. 7 (a small form).

COSCINODISCUS BIANGULATUS SCHMIDT

Central space and rosette absent, markings large, angular, not punctate, with large central papillæ, decreasing toward the border. Border wide, coarsely marked with rows of granules, and with two indentations on the inner side distant from each other about two-thirds of the diameter.

Blue clay.

Pl. [3], Fig. 3.

Distinguished from Coscinodiscus asteromphalus var. omphalantha Grun., which also has two constrictions, by the absence of punctate markings.

COSCINODISCUS ASTEROMPHALUS EHR.