Flexure, a bending.
Fluviatic, of or belonging to a river.
Fluviatile, belonging to fresh water.
Foliaceous, consisting of laminæ or leaves.
Foliated, bent into laminæ or leaves.
Fornix, the excavated part under the umbo. It likewise signifies the upper, or convex shell in the Ostrea.
Fragile, brittle, easily broken.
Front, in univalves, when the aperture is turned towards the observer.
Furcated, forked.
Furrow, a small trench or hollow.