1. Coscinodisceæ.—Valve not divided by rays or costæ into sectors; puncta sometimes radiate; ocelli or processes absent.
2. Actinodisceæ.—Valve with radial striæ divided into sectors: ocelli and processes absent.
3. Eupodisceæ.—Valve disc-shaped with mammiform processes or one or more ocelli.
1. COSCINODISCEÆ
(a) Meloseirinæ.—Frustules short, in chains.
(b) Coscinodiscinæ.—Frustules disc form, usually single, rarely in short chains.
(a) MELOSEIRINÆ
1. Meloseira.—Valve punctate, with a constriction or furrow between edge of valve and girdle.
2. Gaillonella.—Valve punctate, with a circular collar or crest near edge of valve.
3. Lysigonium.—Valve punctate, neither keeled nor constricted.