This is a family very numerous in species, which are generally remarkable for the elegance of their form, the delicacy of their texture, and the brilliancy of their colour. The shell is generally much compressed, greatly produced in breadth, regular, and nearly equal-sided. The hinder side, which is often angular, has an irregular bend or fold at its lower border, more or less conspicuous. The beaks are very small, the hinge varies much, the ligament is swollen and lengthened, the pallial impression deeply hollowed. In general the valves are exceedingly thin and fragile, but painted with the most beautiful colours, often arranged in elegant patterns.