Onycha

spoken of in (Exodus 30:34) was one of the ingredients of the sacred perfume. It consists of the shells of several kinds of mussels, which when burned emit a strong odor.

A nail; claw; hoof, (Heb. sheheleth; Ex. 30:34), a Latin word applied to the operculum, i.e., the claw or nail of the strombus or wing-shell, a univalve common in the Red Sea. The opercula of these shell-fish when burned emit a strong odour “like castoreum.” This was an ingredient in the sacred incense.