PINNULARIA TRIGONOCEPHALA CL.
Valve linear, gibbous in the middle and at the cuneate ends; axial area wider between the middle and the ends, dilated to an elliptical space in the middle; striæ, 6 in 10 µ. L. 145 µ.
Blue clay.
Pl. [29], Fig. 8.
PINNULARIA VIRIDIS NITZSCH
Valve linear-elliptical, with rounded ends; axial area narrow, widened in the middle; striæ, 6 to 7 in 10 µ, crossed by a band as wide as one-third the length of the striæ.
Common in fresh water.
Pl. [29], Fig. 2.
Quite variable in size. Approaches P. major by intermediate forms as in Fig. 9, Pl. [29].
PINNULARIA VIRIDIS VAR. FALLAX CL.