"Cretaceous Egg,'' by Anne Alexander, in the New England Sculptors Association's show "Centennial Visions: 50 Artists in Three Parks,'' marking the National Park Service Association's centennial. The show will run at the Saint Gaudens National Historic Site, in Cornish, N.H., the Marsh-Billings-Rockefeller site, in Woodstock, Vt., and the Springfield Armory, in Springfield, Mass., through Aug. 22.