striæ punctate, nodules elongated Frustulia striæ subtly punctate, central nodule forked Amphipleura striæ punctate and reticulate, in two strata Dictyoneis striæ punctate and alveolate, in three strata Trachyneis striæ punctate, in two strata Brèbissonia striæ interrupted by blank lines Anomoeoneis striæ crossed by longitudinal lines Caloneis striæ oblique, median fissures in opposite directions Neidium striæ punctate and costate, median line with horns Diploneis striæ punctate; valves separated by septate plates Mastogloia striæ punctate, central area dilated into a stauros Stauroneis striæ punctate, area without stauros or horns Navicula striæ costate, not punctate Pinnularia {56}ACHNANTHEÆ Frustules stipitate, free or parasitic. Valves cuneate, elliptical or suborbicular, dissimilar, bent along the transverse or the longitudinal axes, the lower valve with a true raphe and central and terminal nodules, the upper valve with a pseudoraphe or median line. _Rhoicosphenia._--Stipitate; valves with transverse puncta, bent along the transverse axis, cuneate, with diaphragms at the ends. _Anorthoneis._--Free; puncta radiate; valves bent slightly along the transverse axis, suborbicular. _Cocconeis._--Parasitic; valves elliptical, usually bent along the longitudinal axis; striæ punctate, transverse and longitudinal. _Achnanthes._--Stipitate; valves lanceolate or elliptical, bent along the transverse axis; striæ transverse, punctate; costæ sometimes present. RHOICOSPHENIA GRUN. (1860) (rhoicos, curved, and sphen, a wedge) Frustule in zone view curved; valves cuneate, dissimilar, the upper with a pseudoraphe, the lower with a raphe. Chromatophore a single plate along both valves, and one of the inner walls of the zone. Conjugation as in Gomphonema, with which it is generally associated in classification. RHOICOSPHENIA CURVATA (KUETZ.) GRUN. Valve clavate, with rounded apex and base; lower valve with raphe, a narrow axial area and slightly radiate, punctate striæ; the upper valve with a narrow pseudoraphe and parallel striæ; a short diaphragm at the ends of each valve. Length usually from 15 to 25 µ, but frequently of twice the size. Common in Crum Creek. Pl. 19, Figs. 25, 26, 27. ANORTHONEIS GRUN. (1868) (anorthos, not straight) Valves dissimilar, the upper valve with an excentric axial area, the lower with an excentric raphe. ANORTHONEIS EXCENTRICA (DONK.) GRUN. Valves orbicular, with radiating, punctate striæ, closer at the circumference, producing the appearance of a border. Axial area not reaching the ends. Frustules occur free on the sands of the sea-shore. L. 25 to 50 µ. Belmar, N. J. Pl. 16, Figs. 30 and 31. {57}COCCONEIS EHR. (1835) em. GRUN. (1868)