Onycha: A nail; claw; hoof, (Heb. sheheleth;)
(Exodus 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.