Descriptive of the arrangement of pins in a barrel-operated instrument, with the pins arranged in a continuous helix. The barrel continuously shifts sideways as it turns, keeping the keys aligned with the key frame. In this way a long selection (sometimes comprising six or more revolutions of the barrel) may be played without interruption. 2. Helicoidal music box: a cylinder music box with the cylinder pinned in a helicoidal manner instead of the usual manner which requires the cylinder to be shifted in successive steps. In a semi-helicoidal music box, the cylinder is pinned diagonally only at the normal shifting area, permitting music to be pinned across the shifting gap which is normally silent.