TRINACRIA HEIB. (1863) (treis, three, and acra, a point) 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. {31}(_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. KEY TO THE SPECIES Valves costate biddulphiana Valves not costate: Markings cellular, angles elevated into horns favus angles not elevated antediluviana Markings punctate, angles with subconical processes and long spines granulata spines short rhombus spines minute smithii processes truncate, valve elliptical turgida valve orbicular lævis processes absent, valve divided by irregular lines alternans not so divided reticulum BIDDULPHIA BIDDULPHIANA (SMITH) Frustule quadrangular with convex ends and rounded angles. Valve elliptical with undulated sides, divided by septa into three or more sections. Processes large, rounded, globular or subconical. Zone varying in width. Surface with rounded reticulations in longitudinal and transverse rows, except at the centre where they are concentric and smaller. _Conferva biddulphiana_ Smith (English Botany, 1807, Pl. 1762, upper figures). _Diatoma biddulphianum_ Ag. _Biddulphia pulchella_ Gray. Blue clay. Hoboken Tunnel. Along the coast. Pl. 7, Figs. 1, 2, 3, and 4. Quite variable in size and number of septate divisions. Fig. 3 is an unusual form with narrow zone, having but one row of large reticulations, evidently a young frustule. BIDDULPHIA FAVUS (EHR.) V. H. Frustule quadrangular, elevated at the angles into subconical processes oblique to the longitudinal axis. Valve triangular or quadrangular, plane, of two layers, the outer layer composed of large hexagonal cells in rows parallel to the sides, the inner of small puncta radiating from the centre. Zone punctate in quincunx, never found open. _Triceratium favus_ Ehr. Blue clay. Common along the coast.