(achne, froth or down, and anthos, a flower)
Frustules stipitate, solitary or in short fasciæ, flexed. Valves elliptical or lanceolate, naviculoid, dissimilar, the lower with a raphe and median and terminal nodules, and the upper with a pseudoraphe or median space.
The genus has no apparent affinity with any other.
ACHNANTHES LONGIPES AG.
Valves linear-elliptical, obtuse at the apex, sometimes slightly constricted in the middle. Connective zone with transverse, subtly punctate striæ, interrupted by longitudinal lines. Central nodule of lower valve dilated into a stauros reaching the margin. Valves costate, the costæ alternating with double rows of fine puncta.
Along the coast, in estuaries.
Pl. [16], Figs. 1 and 2.
A. longipes is the only species in our locality considered by Cleve as belonging to the genus; the other forms, distinguished by the absence of costæ, are included in the genus Achnanthidium of Kuetzing.
In A. longipes, the chromatophores consist of scattered, rounded granules, while in Achnanthidium the chromatophore is a single plate along the upper valve, or a double one along the connective zone. It is necessary, therefore, to distinguish between A. longipes and the following group, but, because of the long continued union of all of the stipitate forms having the general appearance of a true Achnanthes, I shall continue to describe the local species under the generally accepted name.
ACHNANTHES BREVIPES AG.