One more on the Galacian tradition:

The Cunchas Click Here for a photo (scroll down)(Figure 24)
Figure 24. The Cunchas
Figure 24. The Cunchas.

The cunchas or vieiras (scallop shells) have a privileged rank among the percussive instruments of popular Galician folk music. There is no need for many rules to be able to master and play them; all that is needed is a lot of practice. Place one in each hand, back to back, to obtain sharp sounds by rubbing the tips together; to obtain low sounds, rub the ends together. Another way to obtain different sound effects is to open and close your hands while rubbing the scallop shells together.