The Diatomaceæ of Philadelphia and Vicinity

by Charles S. Boyer

Valve flat, markings rounded, distant, radiate, decreasing toward the border which is coarsely striate. Quite variable in size and in the distance between the markings.

Blue clay and Atlantic coast. Common.

Pl. [2], Fig. 18.

COSCINODISCUS NITIDULUS GRUN.

Valve usually not quite circular; markings smaller than in nitidus and fasciculate near the border.

Blue clay.

Pl. [2], Fig. 19.

Various intermediate forms between nitidus and nitidulus occur.

COSCINODISCUS SUBTILIS EHR.

Markings polygonal, irregular at the centre, but forming numerous fasciculi radiating toward the border, the rows parallel to the central row of each fasciculus. Border narrow with fine striæ; apiculi often present between the fasciculi.