PENNATÆ
Reading edition
Valve zygomorphous. Structure pinnate, not concentric. Valve divided either by a true raphe or cleft or by a linear space or line imitating a raphe.
Divided into three Groups:
1. Fragilarioideæ.—Valves without a raphe; usually with a pseudoraphe or median line.
2. Naviculoideæ.—Either one or both valves with a true raphe.
3. Surirelloideæ.—Valves in which the raphe is concealed near the margin on one or both sides of each valve in a more or less elevated keel or wing.