PINNULARIA BRÉBISSONII (KUETZ.) CL.
Valve linear-elliptical, with rounded ends; axial area narrow, widened into a transverse fascia which is usually broader at the ends; striæ divergent in the middle, convergent at the ends, about 12 in 10 µ. L. 40-60 µ (Cl.).
Fresh water. Common.
Pl. [29], Fig. 12; Pl. [31], Fig. 11.
Variable in outline.
PINNULARIA MORMONORUM (GRUN.)
Valve linear, with rounded ends; striæ divergent in the middle, convergent at the ends, 10 in 10 µ; axial area rhombic-lanceolate, widened to a fascia usually reaching the border. L. 62 µ.
Navicula mormonorum Grun.
Common near Willistown, Pa.
This form is regarded by Cleve as P. brébissonii, but the axial area appears to distinguish it. The valves are sometimes narrowed in the middle.