A Neoclassical amethyst intaglio

A Neoclassical amethyst intaglio, the oval-shaped amethyst plaque engraved with a scene depicting a sea nymph Nereid riding a hippocampus possibly on the way to the wedding of Poseidon and Amphitrite, with a pseudo signature for the ancient engraver Gnaois (active 40-20bc) quartered with seed pearls beneath a hinged seed pearl pendant loop in yellow gold, 4.6cm wide

Believed to have been from the collection of Prince Stanislas Poniatowski