ACHNANTHES EXIGUA GRUN.
Valves oblong-lanceolate, with rostrate ends, sometimes slightly constricted in the middle. Stauros rather wide; striæ punctate, radiating, 22 in 10 µ. L. 10-12 µ.
Stauroneis exilis Kuetz. (not Achnanthes exilis Kuetz.)
Frequently found in aquaria where I have kept it growing continuously for years.
Pl. [16], Figs. 14 and 15.
ACHNANTHES LINEARIS FORMA CURTA H. L. SMITH
Frustules solitary or geminate. Valves linear-elliptical, or elliptical-lanceolate. Lower valve without distinct axial area; upper valve with axial area widened in the middle; striæ slightly radiate (?). L. 7 µ. One of the smallest of diatoms.
This form I found in a pure gathering covering the sides of a greenhouse tank at Elm, N. J. It was sent to Prof. H. L. Smith, who determined it as forma curta of A. linearis.
Pl. [16], Figs. 16 and 17.
ACHNANTHES DANICA (FLOEGEL) GRUN.