Antique onyx cameo in its box

Cameo on onyx. It represents a young woman in bust looking to the left. She is wearing a bonnet adorned with butterfly wings from which her curly hair escapes. She wears a pearl necklace. The cameo is mounted on 18 carat gold, eagle's head hallmark. It is surrounded by fine pearls. It is presented in its original case, in blue velvet and stamped "Poingneux.Mayer successors, boulevard Montmartre. Dimensions of the brooch: 5 cm X 4 cm French work of the 19th century