Clypeus ploti are the 'pound stones' William Smith was finding in the story of the first geological map - The Map That Changed the World'. It's a nice little historical footnote for these great specimens. These urchins are flattish and often slightly crushed, but show clear patterning. Some are polished, others natural, so if you have a preference, please add that as a note on your order and I will try to supply the type you'd like. They are from Gloucestershire in England and are about 140 million years old.