Valve linear, with obtusely rounded cuneate ends, scarcely, if at all, constricted in the middle; longitudinal fold wide; keel puncta, 5 or 6 in 10 µ, sometimes confluent; striæ obscure, about 21 in 10 µ. L. 75 µ. Delaware River. 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 NITZSCHIA DUBIA WM. SM. Valve linear, scarcely, if at all, constricted in the middle, with cuneate, produced, apiculate apices, somewhat recurved; keel very excentric; puncta sometimes partly prolonged, about 9 in 10 µ; striæ, 20-24 in 10 µ. L. 93 µ. Reported from along the New Jersey coast. I have not seen it. It is generally regarded as fresh-water. Slides sometimes labelled N. dubia are in reality N. litoralis var. delawarensis. Pl. 39, Fig. 5. The figure is drawn from a specimen from another locality. BILOBATÆ NITZSCHIA BILOBATA WM. SM. Valve linear-lanceolate, constricted in the middle, apiculate at the ends; keel puncta 6 in 10 µ, prolonged unequally across part of the valve, the two median sub-remote; striæ, 16 in 10 µ. Frustule oblong, truncate, constricted in the middle. L. 120 µ. Shark River, N. J., Chester River, Md. Pl. 32, Figs. 10 and 11. EPITHEMIOIDEÆ NITZSCHIA EPITHEMIOIDES GRUN. Valve linear, with cuneate, rostrate apices; slightly constricted on the keel side; keel puncta, 8 or 9 in 10 µ, extending as costæ across the valve; striæ delicate, 22 in 10 µ. L. 47 µ. Brackish water, Long Island Sound. Pl. 32, Fig. 21. {119}GRUNOWIA NITZSCHIA TABELLARIA GRUN. Valve rhomboidal, inflated in the middle; apices produced; keel puncta extend in costæ across half of the valve, 7 in 10 µ; striæ transverse, about 22 in 10 µ. L. 20 µ. _Dimerogramma sinuatum_ Thwaites. _Nitzschia sinuata_ var. _tabellaria_ (Grun.) V. H. Schuylkill River. Not common. Pl. 32, Fig. 7. SCALARES NITZSCHIA SCALARIS (EHR.) WM. SM. Valve linear, with obtusely conical apices; costæ transverse, extending more or less to one-third the width of the valve, 3 or 4 in 10 µ; striæ, 9 or 10 in 10 µ, punctate. Length of valve quite variable, up to 480 µ (Cleve). A well-known form, abundant in salt marshes and more or less brackish water. Pl. 33, Fig. 6. (To the right of the figure is an outline of the valve reduced one-third.) INSIGNES NITZSCHIA INSIGNIS GREG. Valve nearly linear or linear-lanceolate; apices broad, slightly produced, obtuse; keel puncta extended into short costæ, 4 or 5 in 10 µ; striæ about 14 in 10 µ. Length variable up to 400 µ.