The set of clam shells is known as kaiawase, a type of game created during the Heian Period (794-1120). The shells would be spread on top of a tatami mat and two people will try to match the set of shells. Later, the set became an essential part of a lady's dowry and various sets were created. Beautifully painted in detail with scenes from the Tale of Genji in mineral colors and gold leaf with raised gofun patterns. Each pair of shells in this fits perfectly together. Meiji Period. Size: 3 1/2" wide and 3 3/8" wide