"Plurry"is my name for an imaginary musical instrument that reveals much about the mathematical basis of music. What makes it different is not the material it is made of - it could be a string or percussive or electronic mechanism - but the spatial arrangement of the tones. They are arranged not in one dimension but two - roughly, octaves and twelfths. If could be a teaching tool. Certain tone-series, which I call plures, would be played on it with simple actions; and the actions for playing in all keys would be the same. One reader built a prototype and was enthusiastic about its ease of playing.