Pl. [10], Figs. 5 and 6. Fig. 11, Pl. [40], shows frustules containing the nuclei and chromatophores.
DIATOMA HIEMALE (LYNG.) HEIB.
Valve ovate-lanceolate to lanceolate; apices obtuse, not produced. Costæ not numerous, robust; striæ moniliform. Zone view quadrate, the costæ as septa deeply dividing the valve into convex elevations.
Common in springs.
Pl. [10], Figs. 7 and 8.
In all species of Diatoma a punctum, or pore, is observed, usually at alternate ends of the two valves, by means of which a communication exists between adjoining frustules and causes them to adhere in zig-zag chains when partially separated.
Plagiogramma Grev. (1859)
(plagios, on the side, and gramma, a letter)
Frustules quadrangular, adnate in fasciæ, or free. Valve linear, elliptical, or elliptical-lanceolate, divided by two or more median and two terminal costæ or with a central and two terminal hyaline spaces.
| Valve with two median and two terminal costæ: | |
| Linear, pseudoraphe distinct | pygmæum |
| Linear, with striæ at the ends | wallichianum |
| Ovate-lanceolate | obesum |
| Valve without costæ but with central and terminal nodules: pseudoraphe absent | tessellatum |