Masks of woven fibre with nassa and cowrie shells attached are restricted to only a few groups of villages on the north coast of PNG, to the west of Madang. All other villages in this quite extensive cultural region carve and use wooden masks. They are called dema in one language group, and bilibili in the adjacent group. Unlike wooden masks, these dema are more susceptible to deterioration, so few ancient examples exist, except as fragments. Legend says that a sea spirit first taught this technique to an old, infirm man, left behind in a village when everyone departed to attend a ceremony far from home. He passed this knowledge on but the technique has remained confined to a quite small area. These masks are highly prized as only a few men make them, and they are also used as wealth objects at bride price and other transactional rituals.