A LIMAÇON is a 4th-degree curve, a higher-order symmetry operation and recursive function in which the curve turns within itself, inverting its interior and exterior parameters. Masons and master masons all over the world have traditionally had "mason's marks" to identify their work in their craft. I was first inspired by this symbol and its significance in my early career and it has traveled around the world with me— I have found hints of this symbol in the geometries of French masons, Catalan masons and even Indian carvers. I think that the Limaçon is a befitting symbol for the complexity of shell design— where organic form and geometry, structural engineering, material science and construction are all synthesized in the mastery of craft.