Jennifer, I have used a small X-ray machine to study shell thickness in Littorinidae shells ("winkles"). Regards, Bill P. ********************************************************************** * Charles (Bill) Pettitt * Keeper of Invertebrates * * * (& network supervisor) * * E-mail: [log in to unmask] * Manchester Museum * * * University of Manchester * * Tel: +44.61.275.2666 * Manchester M13 9PL * * Fax: +44.61.275.2676 * United Kingdom * **********************************************************************