Michael Reagin wants to know about modern calcitic gastropods. Can't help you there, but Tertiary Ecphora is indeed calcitic, and so is Cretaceous Striaticostatum, which looks much like Epitonium. Aragonite is harder than calcite, but less resistant to solution. I don't know why a gastropod lineage would switch from aragonite to calcite. Snails display a wide array of shell structures, many of which have crystals laid down in different directions to strengthen the shell, the way that wood grain at right angles strengthens plywood. Andrew K. Rindsberg Geological Survey of Alabama