Tylocidaris clavigera (Mantell, 1822) cast of a sea urchin fossil found in England.  The creature existed in the Cretaceous Period.  Cast...

Stereocidaris hemigranosus sea urchin fossil on display at the Smithsonian National Museum of Natural History in Washington, DC.  The fos...

On the right is a Macrocrinus mundulus crinoid with its stem, calyx and anal tube intact.  The fossil on the left is an intact blastoid ...