I'll leave to others to comment on the habits of Crepidula fornicata, which were indeed accurately portrayed in the article reproduced by Dominic Rawlingson Plant. I will tell you about Crepidula princeps instead. Crepidula princeps (princeps = "chief", later "prince") is a large slipper snail that lived on the California coast during the Pliocene Epoch. Its habits must have been similar to those of C. fornicata, because specimens are preserved in curving stacks of 6 or more snails. In fact, this was one of the first fossils that I encountered on a field trip as an undergraduate. The professor, Norm Silberling, took us to San Gregorio beach in central California to show us sedimentary rocks. Many of the best outcrops in California are seacliffs, which can be distracting due to their natural beauty. In fact, Norm later told me that he nearly flunked his first geology course because he paid more attention to watching birds than rocks. But to return to the story, I was thrilled to find ammonites in the cliff at San Gregorio, and pointed them out to the professor. He didn't know what they were, but he did remark that the rock was Pliocene. Even I knew that the last ammonite died more than 60 million years before that. I would have been better off calling them nautiloids, which they resembled more closely than ammonites, but I wasn't very knowledgeable about mollusks then. They remained a mystery that day. I later learned that they were neither nautiloids nor ammonites, but stacks of the gregarious slipper snail, Crepidula princeps, and a rare example of fossilized reproduction. Thanks for bringing back the memory, Dominic. I wish I could be there now on that cool, windy beach, building sand castles and taking a long walk on the beach below the tall, yellowish, fossiliferous cliffs. Andrew K. Rindsberg Geological Survey of Alabama