Constant Lambert's ballet Tiresias, recently recorded on Hyperion,
probably fits the bill. Quoting from the booklet: "... not a likely
ballet scenario, with the stage requirement of the lead character changing
sex, two snakes copulating, an argument about which of the sexes enjoys the
sexual act the most, a downbeat ending, and a convoluted story not familiar
to the general public."
-- Art Scott
Livermore, Cal.