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.
The quadrangular form occurs only southward.
Pl. [6], Fig. 6. At "a" a cell showing the lower punctate layer. Pl. [40], Fig. 16, a transverse section of a portion of the valve showing the cellular structure and the punctated lower stratum.
BIDDULPHIA ANTEDILUVIANA (EHR.) V. H.
Frustules quadrangular, sometimes united in zig-zag chains. Valve quadrangular with more or less concave sides, sometimes cruciform. Surface with angular cells arranged in concentric and radiating lines increasing toward the circumference. At each angle is a large, rounded process, which, as well as the secondary layer, scarcely visible, is finely punctate.
Amphitetras antediluviana Ehr.
Amphitetras tessellata Shad.