Such mother-of-pearl bowls were used on Yap Island as a means of payment for specialist services, such as healing or tattooing. They also functioned as a return gift if food was given to a group or village on special occasions. They were classified as less valuable within the profusion of currencies on Yap - including the famous »stone money« - because it was abundant across the islands as a raw material. Shell money from large mother-of-pearl shells that had to be imported, on the other hand, was deemed highly valuable.