SOUTHAMPTON, N.Y.- American Portraits: Treasures from the Parrish Art Museum, the fourth in a series of special exhibitions drawn exclusively from the Parrish’s collection, will showcase some of the truly exceptional works of art in a variety of media, including painting, drawing, and photography that illustrate the many and varied ways in which artists approach portraiture. The exhibition, organized by Alicia Longwell, Lewis B. and Dorothy Cullman Chief Curator, Art and Education, will open October 16 and remain on view through November 27. William Sidney Mount’s Portrait of Mrs. Manice (1833) is the earliest painting in the Parrish collection and a strong example of the importance of portrait painting in the early years of the nation, assigning both status and prominence to the sitter. Mount painted many of Long Island’s best known citizens,