Valve semi-elliptical, obtuse at the apices, which are sometimes prolonged and turned downwards; median line straight, terminal nodules distant from the ends; axial area narrow, central area rounded; striæ in radiating, slightly curved lines, indistinctly punctate. Common in fresh water; occasional in brackish. Pl. 18, Fig. 21 (represents a frequent variation). CYMBELLA PHILADELPHICA N. SP. Valve semi-elliptical-lanceolate, with rounded apices; ventral margin strongly gibbous; terminal nodules distant from the ends; axial area broad, central area widened on the dorsal side; striæ radiate, not curved nor of unequal length, indistinctly punctate, 10 in 10 µ on the dorsal, 8 in 10 µ on the ventral side. L. 86 µ. This form approaches Encyonema prostratum (Berk.) Ralfs, Schmidt's Atlas, Pl. 71, Fig. 7, but differs in the striæ and the axial and central areas. Blue clay of Philadelphia. Rare. Pl. 18, Fig. 8. CYMBELLA TRIANGULUM (EHR.) CL. Valve semi-elliptical, with acute ends; median line straight; ventral side half the width of the dorsal, with straight, slightly convex or concave margin; striæ radiate, coarsely punctate. _Gloeonema triangulum_ Ehr. Baker's Run, Willistown, Pa. Pl. 18, Fig. 24. CYMBELLA TURGIDA (GREG.) CL. Valve semi-elliptical, with acute ends; ventral margin gibbous; ventral side half the width of the dorsal; median line straight; terminal fissures turned downwards; axial area broad; striæ radiate, coarsely punctate. Baker's Run, Willistown, Pa. Pl. 18, Fig. 23. CYMBELLA TURGIDA (GREG.) CL. VAR. ? Valve lunate, with gibbous ventral margin; median line straight; terminal fissures turned downwards near the ends; axial area lanceolate, striæ radiate on the dorsal side, 8 in 10 µ, punctate, 9 on the ventral side, closer at the ends where they are convergent. L. 65 µ. Not a typical form. Willistown, Pa. Pl. 18, Fig. 12. CYMBELLA RHOMBOIDEA N. SP. Valve rhomboidal, with acute ends; dorsal part one and a half times the width of the ventral; median line nearly straight, with terminal fissures turned downwards near the ends; axial area broad, not widened in the middle, except slightly on the ventral side; striæ {64}radiate, distant in the middle of the dorsal side where they are 7 in 10 µ, coarsely punctate, the puncta in longitudinal lines, 9 in 10 µ on the ventral side, closer at the ends. L. 69 µ. Baker's Run, Willistown, Pa. Pl. 18, Fig. 11. CYMBELLA GRACILIS (RAB.) CL. Valve semi-lanceolate, with acute ends; median line nearly straight, with terminal fissures turned downwards, distant from the ends; axial area linear; ventral margin straight or slightly gibbous in the middle. Hammonton Pond, N. J. Pl. 18, Fig. 20. CYMBELLA LACUSTRIS (AG.) CL. Valve elliptical-lanceolate, with obtuse ends, nearly symmetrical; median line straight, terminal fissures distant from the ends; striæ radiate in the middle, convergent at the ends, coarsely lineate. Belmar, N. J. Pl. 18, Fig. 25. AMPHORA EHR. (1840)