The development of Cordium edule is described from the fertilization of the eggs to the completion of metamorphosis. Cleavage and gastrulation are similar to those processes in other lamellibranchs. Differentiation of the major larval organs, the velum, the larval retractor muscles and the digestive system is completed within the first four days of life. Other organs are relatively undeveloped until the veliger is twenty-two to twenty-five days old. Differentiation is not complete until the spat have settled for several weeks. The larval retractor muscles are paired and are attached around the mouth and to the presumptive foot region as well as to the velum.