Large navette-shaped portrait miniature c.1790 of a young pale fashionable beauty with pearls adorning the hair wearing  a sky blue dress and ribbon at the neck.
Circle of Ozias Humphry(1742-1810).
2 inches by 1.5inches.
Humphry was born in Devonshire, moved to Bath where he had rooms in the house of Thomas Linley, the musician, and then went to London where, in 1764, Sir Joshua Reynolds persuaded him to settle. He spent time in Italy (1773-7) and a brief period in India (1785-7), exhibited at the Royal Academy between 1779 and 1797 and became a Royal Academician in 1791. His sight began to fail in 1792 when he turned to drawing in oil and pastel, and in the same year he was appointed Painter in Crayons to George III. He became blind in about 1797-8.
This beauty strikes me as highly reminiscent of the work of Sir Joshua Reynolds but I have thus far been unable to identify a portrait match.