Pl. [19], Fig. 2.
Pl. [38], Fig. 15, zone view of young frustule.
GOMPHONEIS MAMILLA (EHR.) CL.
Valve lanceolate, with rounded apex and base; striæ costate, 10 in 10 µ, alternating with double rows of fine puncta; axial area linear, sometimes oblique, central area small, with one or more stigmas.
Blue clay. Rare.
Pl. [19], Fig. 1.
In one frustule I noticed one valve with one stigma and the other with four stigmas.
The difference between G. mamilla and G. elegans is not very great. In the latter the central area is larger and the longitudinal lines not so near to the margin. The stigmas form a circlet. There appears to be a coincidence in the relation of Gomphoneis to Gomphonema, and that of the true Achnanthes to the group described by Cleve under Achnanthidium. In Gomphoneis and Achnanthes the striation is both costate and punctate while in Gomphonema and Achnanthidium the striation is punctate only.
Gomphonema AG. (1824)
(gomphos, a peg, and nema, a filament)