(amphi, on both ends, and prora, a prow) Frustule twisted in the longitudinal axis, constricted in the middle; zone complex, with numerous divisions crossed by fine striæ. Valve lanceolate, acute. The raphe confined within a sigmoid keel or extension of the valve; the central and terminal nodules indistinct. Striæ transverse, punctate, with coarser striæ at the junction of the keel and lower part of the valve. Chromatophores single, with indented border except in A. pulchra, in which there are two chromatophores with entire borders. AMPHIPRORA ALATA KUETZ. Frustule with a row of puncta at the junction line. Valve linear, acute at the ends. Median line sigmoid. Striæ lineate on the lower part of the valve, punctate on the keel. Along the coast. Not common. Pl. 14, Fig. 3. AMPHIPRORA PULCHRA BAIL. Frustule with sigmoid connective zone. Valve very convex, with sinuate keel and junction lines evident. In zone view and in valve view, one half of the frustule, owing to the elevation of the keel, is wider than the other half. Striæ punctate, coarser on the keel. Not uncommon along the coast. Pl. 14, Figs. 1 and 2. AMPHIPRORA CONSPICUA GREV. Valve linear or elliptical, with acute ends. Median line sigmoid, but the junction lines not evident. Striæ lineate, with coarser lines near the middle. Not common. Port Penn, Delaware River. Pl. 14, Fig. 4. AMPHIPRORA ORNATA BAIL. Frustule membranaceous, constricted in the middle, with well-marked folds extending from the junction line in both directions. Valve lanceolate, constricted in the middle and with protracted ends. Keel undulate on the edge. A beautiful, transparent and delicate form, the only fresh-water species in our locality. Delaware Water Gap, Pa. Pl. 14, Figs. 6 and 7. AMPHIPRORA PALUDOSA WM. SM. Frustule membranaceous, constricted, with truncate ends. Valve linear, with acute ends. Striæ scarcely visible. Cape May (Cleve). Pl. 14, Fig. 5. TROPIDONEIS CLEVE (1891) (tropis, a keel) Frustule oblong, constricted in the middle; keel not sigmoid. Axial area not evident. Striæ very fine, punctate, in longitudinal lines. {69}TROPIDONEIS LEPIDOPTERA (GREG.) CLEVE Valve with straight, median excentric line. Keel unilateral, projecting above the median line in zone view; central area small. Transverse striæ finely punctate. As usually seen, the valve is inclined. According to Karsten there are two chromatophores on the connective zone, each divided into four parts, each of which contains a large oval pyrenoid. _Amphiprora lepidoptera_ Greg. Along the coast. Pl. 14, Figs. 8 and 9. AURICULA CASTRACANE (1873) (auricula, the ear, the shape of the valve) Frustule globose. Valve reniform or cymbiform, elevated into a keel which is not sigmoid. Median line biarcuate. Differs from Amphiprora in not having a sigmoid keel. AURICULA MUCRONATA (H. L. SMITH) PERAGALLO