The Diatomaceæ of Philadelphia and Vicinity

by Charles S. Boyer

Valve triangular, angles elevated into spines. Cells at the margin large.

TRINACRIA PILEOLUS (EHR.) GRUN.

Valve with concave sides. Surface concave with unequal punctiform and scattered markings with central dots. Cells at the margin large, rounded. At the angles, which vary in elevation, a few puncta are seen.

Triceratium pileolus Ehr.

Blue clay. Rare.

Pl. [6], Fig. 9.

(b) BIDDULPHIINÆ

Biddulphia Gray (1831) em. Van Heurck (1885)

(a genus, constituted from Conferva biddulphiana of the English Botany, named after a Miss Biddulph)

Frustule prismatic or subcylindrical, concatenate, filamentous, or in zig-zag, or, as usually found, free. Zone well developed. Valve triangular, polygonal, elliptic or subcircular, convex, more or less elevated at the angles into processes or horns. Markings cellular or punctate. Chromatophores, small plates of various forms.