Some time ago, James Cheshire asked whether cowries really can emit sulfuric acid, as reported. I don't know, but sulfuric acid, a very corrosive substance, is not unknown in nature as a defense. In "Marine Algae of California" (Stanford University Press, Stanford, California, 1976, p. 220), I. A. Abbott and G. J. Hollenberg state that the seaweed Desmarestia is "remarkable in the field owing to large amounts of acids produced when plants are collected, bleaching nearby plants and producing an acrid odor." I have elsewhere seen it suggested that sulfuric acid is in this mix. It would be very remarkable if any shelled mollusk used any acid as a defense, considering the harm that might occur to the shell, but nature is remarkably inventive. Does anyone know of any examples? Andrew K. Rindsberg Geological Survey of Alabama