Polyhymnia

Polyhymnia, Monte Calvo, 2nd century A.D., Marble, Nye Carlsberg Glyptotek (Copenhagen, Denmark). Made with Memento Beta.
The rotating movement emphasised by the right hand holding her cloak shows that the woman is dancing. She is Polyhymnia, the Muse of Dance.
Polyhymnia (“the one of many hymns”), also spelt Polymnia was in Greek mythology the Muse of sacred poetry, sacred hymn, dance, and eloquence as well as agriculture and pantomime. She is depicted as very serious, pensive and meditative, and often holding a finger to her mouth, dressed in a long cloak and veil and resting her elbow on a pillar. Polyhymnia is also sometimes credited as being the Muse of geometry and meditation. (Wikipedia)