The Diatomaceæ of Philadelphia and Vicinity

by Charles S. Boyer

Pl. [3], Fig. 9.

In the fossil forms the puncta are not evident, hence the species is usually described as not punctate.

COSCINODISCUS RADIATUS EHR.

Markings polygonal, slightly decreasing toward the border where they are much smaller; border well marked, striate. Quite variable in size.

Common in the blue clay and along the coast.

Pl. [3], Fig. 11. Fig. 1 is probably a smaller form.

COSCINODISCUS SUBAULACODISCOIDALIS RATTR.

Markings small, decreasing toward the border in somewhat fasciculate rows. About one-third the distance from the border are five (Rattray finds six) well-marked apiculi somewhat resembling those of Aulacodiscus. Border narrow, hyaline.

Rare in the lower stratum of the blue clay.

Pl. [3], Fig. 4.