Oops! In my last post, the line: Bivalves which live in shallow water, in climates which fluctuate between frigid and warm, may have true annular growth rings . . . should have read: Bivalves which live in shallow water, in climates which fluctuate between frigid and warm, may have true ANNUAL growth rings . . . All growth rings are annular (ring-shaped), but not all are annual (yearly). Paul M.