See Cycloid, Ctenoid, and Ganoid.5. (n.) Hence, any layer or leaf of metal or other material, resembling in size and thinness the scale of a fish; as, a scale of iron, of bone, etc.6. (n.) One of the small scale like structures covering parts of some invertebrates, as those on the wings of Lepidoptera and on the body of Thysanura; the elytra of certain annelids.