The Diatomaceæ of Philadelphia and Vicinity

by Charles S. Boyer

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.