Valve clavate, broad at the sub-truncate apex and slightly constricted, or with parallel margins; axial area linear, central area stellate, with one stigma; striæ in the middle alternately longer and shorter. Blue clay. Pl. 19, Fig. 22. {73}GOMPHONEMA PARVULUM VAR. MICROPUS (KUETZ.) CL. Valve clavate, with rounded apex and basis; axial area indistinct; central area unilateral, with a small stigma; striæ distant in the middle. Common. Pl. 19, Fig. 17. GOMPHONEMA VENTRICOSUM GREG. Valve clavate, with broad apex and produced, rounded basis; axial area narrow, widened in the middle; stigma one; striæ distant in the middle, finely punctate. Blue clay. Pl. 19, Fig. 13. GOMPHONEMA OLIVACEUM LYNG. Valve clavate, with broad apex and narrow basis; axial area very narrow; central area irregular, without stigma; striæ radiate, finely punctate. Very common. Pl. 19, Fig. 23. GOMPHONEMA BRASILIENSE VAR. DEMERARÆ GRUN.? Valve lanceolate, with sub-cuneate apex and narrowed basis; axial area lanceolate, broad; no stigma; median fissures remote; striæ parallel, 12 in 10 µ, punctate, the puncta obsolescent, small or interrupted. Willistown, Pa. Rare. Pl. 19, Fig. 24. PLEUROSIGMA WM. SM. (1852) (pleura, a side, and sigma, the letter s) Valve lanceolate, sigmoid; axial area very narrow, central area small; striæ punctate, in transverse and oblique lines. Cleve divides the forms usually known as Pleurosigma into two genera, Pleurosigma and Gyrosigma. Pleurosigma includes all forms having oblique rows of puncta, while Gyrosigma includes all having longitudinal rows. Both have transverse striæ. The former consists entirely of marine species, while in the latter the species are found in fresh, brackish and salt water. The endochrome in Pleurosigma, according to Mueller, consists of two bands which differ in the median part of each valve. Mereschkowsky says that the endochrome is so divided as to form four bands, two on each valve, that their position is different in different species, and that they are not the same on valves of the same frustule. Cleve prefers to classify the species of Pleurosigma and Gyrosigma in accordance with the outline of the valve and the flexure of the median line. I shall, however, retain the method used by Peragallo and Grunow and arrange the forms according to the striation. (1) OBLIQUE STRIÆ ABOUT 90 DEGREES, MORE DISTINCT THAN THE TRANSVERSE PLEUROSIGMA FORMOSUM WM. SM. Valve elongated, slender, gently sigmoid, acute at the ends; oblique striæ crossing each other at about 90 degrees; 10-16 in 10 µ; transverse striæ, 14-20 in 10 µ (Cleve). Along the coast. Pl. 22, Fig. 5. {74}PLEUROSIGMA OBSCURUM WM. SM. Valve linear, not sigmoid, or scarcely so; ends obtuse, subconical; raphe sigmoid, near the margin at the extremities; transverse and oblique striæ equidistant, 28 in 10 µ (Wm. Sm.). Abundant at Greenwich Point, Philadelphia. Pl. 22, Fig. 4. (2) OBLIQUE STRIÆ CLOSER AT THE ENDS