An amethyst and ruby ring, circa 1800, designed as a floral cluster, set with a cabochon amethyst

An amethyst and ruby ring, circa 1800, designed as a floral cluster, set with a cabochon amethyst within a border of flat-cut rubies, the reverse applied with black and white enamel, to a band incised with floral scrollwork accented with black enamel, mounted in gold, size O, one ruby replaced with an onyx, amethyst possibly a later replacement, possibly converted from a button, case