Large samples collected, measured, and returned to the beach at monthly intervals at La Jolla, California, for five successive years showed an average initial set of 3 young clams per sq m in an area of 2000 sq m. The annual mortality has been from 67 to 75% for each year-class. Of an annual set of 6000, only 2000, 700, 170 and 50, respectively, have remained at the end of the first to fourth years. The length increases about 21 mm per year for the first two years of life and somewhat less thereafter. Less than one per cent survived long enough to reach the legal length of 127 mm....