PARIS.- The sale of furniture, works of art and sculpture to be staged at Sothebys Paris on November 10 reflects the diversity and richness of the decorative arts in 18th century France. Among the 300 lots to be offered for auction is a magnificent Louis XV ebony bureau plat with cartonnier (c.1765-70), stamped Montigny, topped by a gilt-bronze clock with a movement signed Bouchet à Paris (est. 500,000-800,000). This is one of the few bureau by Philippe-Claude Montigny (who qualified as maître in 1766) with an ebony-veneered cartonnier; most were in marquetry. It is also exemplifies the à la grecque (Greek) style introduced to France shortly