THE SHAPES OF CHANGE: IMAGES OF AMERICAN DANCE by Marcia B. Siegel (University of California: $30, hardcover; $8.95, paperback). This book serves as an important survey of the development of American dance from Denishawn to Twyla Tharp. Marcia Siegel offers valuable descriptions of more than 40 works and argues convincingly that dance classics frequently have degenerated in their later revivals. (Siegel identifies the causes to be changes in the choreographers' intentions, chronological distance from the originals and, especially, the different weight and attack that today's ballet-trained modern dancers bring to these works.) Of key importance also is the way that Siegel sees American dance as a whole, valuing equally the contributions of both ballet and modern dance choreographers. One may disagree with her hard judgments regarding the works of Agnes de Mille and of Martha Graham after the 1940s, among others; lament the exclusion of certain favorite dances, and regret occasionally bogging down in methodical description. But overall, Siegel's book brings a valuable vision and record to dance literature.