Pl. [32], Fig. 12.
This form is drawn from a slide of Christian Febiger containing an abundance of specimens from Delaware City, and marked "Nitzschia dubia."
Circumsutæ
NITZSCHIA CIRCUMSUTA (BAIL.) GRUN.
Valve elliptical, sometimes more than 200 µ in length; longitudinal fold more or less conspicuous; keel puncta about 4 in 10 µ, the middle distant with the appearance of a nodule; striæ irregular, subtle, finely punctate, frequently interrupted.
Surirella circumsuta Bail.
Tryblionella scutellum Wm. Sm.
Common in brackish water.
Pl. [32], Fig. 1.
Dubiæ