Cassiduloida

Cassiduloida, one of the orders of Sea Urchins (Echinoidea), including those forms which possess a "floscelle," and which are not provided with jaws. A floscelle consists in the development of a star-shaped ornamentation around the mouth, by the ambulacra becoming expanded and depressed, and the intervening areas being raised into ridges. Living species are mainly tropical, and many are deep sea. Among British fossils of this order is the Jupiter's Cap (Galerites albogalerus), one of the best known chalk fossils, and the flat Cake Urchin (Clypeus sinuatus), common in the inferior oolite rocks of the Cotteswolds.