Palaeechinoidea

Palaeechinoidea, a sub-class of Echinoidea, or Sea-Urchins, including all the Palaeozoic and some Triassic species. The only character by which it differs from the other sub-class, or Euechinoidea, is that the plates are not arranged in twenty zones. It includes four orders - the Bothriocidaroidea, Perischoechinoidea, Plesiocidaroidea, and Cystocidaroidea. Palaeechinus is the best-known genus.