Occasional in streams and in the blue clay. Abundant in a water-trough at Ashbourne, Pa.
Pl. [21], Fig. 8.
I have retained Lewis' name as specific. Lewis, wrongly, I think, ascribes his species to Navicula trinodis Wm. Sm., which is not figured by Smith, but is illustrated by Van Heurck (Syn. Pl. 14, Fig. 31a), and is named by Cleve Navicula contenta var. biceps Arnott. De Toni includes Lewis' name under Rhoiconeis trinodis (Wm. Sm.) Grun. Rhoiconeis is achnanthiform, with frustules arcuate, and the species is named by Cleve Achnanthes trinodis (Arnott). Caloneis schumanniana (Grun.) Cl., to which as a variety Cleve unites Lewis' form, appears to resemble it only in the lunate marks.
Fig. 9 represents a single specimen found in the Pavonia deposit and which I believe to be an abnormal form of C. trinodis, differing only in the degree of inflation and in the larger central area.
Navicula trinodis var. inflata Schultze, from Staten Island, is the same form figured by Lewis, who states that certain specimens have produced apices.
CALONEIS PERMAGNA (BAIL.) CL.
Valve lanceolate, with produced apices; median line nearly straight; axial area lanceolate, irregular or slightly unilateral, about half the width of the valve; striæ, 9 in 10 µ, radiate and indistinctly punctate; longitudinal lines double. L. 100-200 µ.
Pinnularia permagna Bail.
Common in brackish water.
Pl. [21], Fig. 1.