Onycha
ONYCHA o’ nikă (שְׁחֵ֫לֶת, H8829), the operculum of a species of Strombus, or other marine mollusks, which emit a penetrating aroma when burnt. It was one of the ingredients of the incense used in the Mosaic ritual (Exod 30:34—tr. “aromatic shell” in NEB, including Ecclus. 24:15). The Red Sea, an isolated warm water pocket of the Indian Ocean, is noted for its peculiar subspecies of mollusks, including the Liniated Conch (Strombus fasciatus Born)
International Standard Bible Encyclopedia (1915)
"Onycha" is a transliteration of the Septuagint onucha, accusative of onux, which means "nail," "claw," "hoof," and also "onyx," a precious stone. The form "onycha" was perhaps chosen to avoid confusion with "onyx," the stone. The Hebrew shecheleth occurs only in Ex 30:34 as an ingredient of the sacred incense. It is supposed to denote the horny operculum found in certain species of marine gasteropod molluscs. The operculum is a disk attached to the upper side of the hinder part of the "foot" of the mollusc. When the animal draws itself into its shell, the hinder part of the foot comes last, and the operculum closes the mouth of the shell. The operculum, which may be horny or stony, is absent in some species. The horny opercula when burned emit a peculiar odor, and are still used in combination with other perfumes by the Arab women of Upper Egypt and Nubia. (See Sir S. Baker, The Nile Tributaries of Abyssinia, cited by EB, under the word "Onycha.")