The Echinoid Directory

Stem group Neognathostomata with:

• apical system compact and tetrabasal;
• petals present, subparallel, open distally and ending gradually; ambulacral plates beyond petals double pored;
• phyllodes well developed, bowed, with a distinct inner series of pore-pairs in each half ambulacrum; no buccal pores;
• bourrelets: basicoronal plates small and short, interambulacra raised towards peristome forming pseudobourrelets;
• peristome sunken; specialized perioral spines and tubercles lining the vertical walled entrance to the peristome entrance;
• periproct small, flush, on posterior face or just inframarginal;

Middle Jurassic (Bajocian) to Upper Cretaceous (Cenomanian).