King Arthur, a Masque by Purcell. The New York City Opera. The real star of this delightful confection based on Purcell's King Arthur is the great choreographer Mark Morris and his brilliant company of beautiful dancers, the Mark Morris Dance Group. While the story line is more or less a series of pastoral vignettes, the wit and imagination of Morris and the designers Isaac Mizrahi and Adrianne Lobel bring a unifying wittiness and enormous charm to the whole. Though the singers are less prominent, the young and lovely soprano Melissa Fogarty, a last minute replacement scored a triumph, singing with delectable and highly skillful coloratura and is surely on her way to a successful career. But in the end, it's all about the dancing and staging and this was a riotous joy from start to the great Frost Scene, the Maypole Dance and the glorious and happy conclusion. The audience left the theater on a palpable high. Broadway Bridge and Tunnel Test. B+