Tiny Sea Urchin

So sweet! This is a very rare Cretaceous echinoid (sea urchin), Boletechinus. They are typically no more than a couple mm in diameter. This one is shown next to a pencil eraser. Most of the ones in the Smithsonian's collection come from sand and silt removed for the creation and maintenance of a canal, which exposed fossils well below the surface. This one comes from New Castle County, Delaware.