The Diatomaceæ of Philadelphia and Vicinity

by Charles S. Boyer

Frustule linear, sigmoid; valve linear, slightly sigmoid, tapering to the sub-acute apices; keel excentric, puncta, 8 in 10 µ; striæ, 20-24 in 10 µ. L. to 250 µ.

Along the coast.

Pl. [39], Fig. 13.

NITZSCHIA SIGMATELLA GREG.

Valve linear, sigmoid, slightly attenuated toward the obtuse apices; keel excentric, puncta, 8-10 (?) in 10 µ; striæ delicate, 25-30 in 10 µ. L. to 400 µ. The keel puncta are quite obscure.

Nitzschia curvula Wm. Sm.

Nitzschia sigma var. curvula (Wm. Sm.) De Toni.

Fresh water. Hammonton Pond; May's Landing, N. J.

Pl. [33], Figs. 4 and 5.

Gregory remarks that the keel puncta are seen in some specimens. In both of the forms figured I have counted 30 striæ in 10 µ, but, after many examinations, I have not been quite certain about the keel puncta. The general appearance of the valves in any position is that of a Stenopterobia or Surirella anceps, with which it occurs.