It was a percussion instrument (like the tambourine) that was mainly used by the Corybantes in their rituals.

It consisted of a shallow wooden cylindrical frame with a stretched leather membrane on its base. Pairs of hammered bronze discs were fitted in notches perimetrically to the frame that clapped when the instrument was used.
Execution was similar to that of the drum.

SOURCES: Solon Michailidis, Encyclopaedia of Ancient Greek Music, Plutarch, On Music.