The Echinoid Directory

• Test small, depressed.
• Apical disc rather large, dicyclic; firmly bound to corona. All plates covered in pustular granules. Periproct small.
• Ambulacra simple adapically with one granules on each plate; pore-pairs small, oblique and uniserially arranged. Immediately beneath ambitus p-lating becomes trigeminate with large tubercle covering all three elements; tubercles and plating continues like this to peristome. All elements in compound plate reach perradius and upper and lower element slightly smaller than central element.
• Interambulacral plates only a little wider than tall. Each plate bears a large primary tubercle with a large imperforate mamelon; platform almost obsolete, but in best preserved tubercles there is fine crenulation.
• Adradial margins of interambulacral zones with lateral grooves and aligned granules close to peristome.
• Peristome slightly sunken, about 50% test diameter. Buccal notches open and shallow; interambulacral margin raised as a low lip.
• Spines and lantern unknown.

Pleurodiadema sturtzi (Moesch, 1867), by original designation.

• P. sturtzi (Moesch, 1867); Oxfordian, Europe.
• P. nudum Cotteau, 1875; Kimmeridgian, France.
  
• P. gauthieri Cotteau, 1875; Bathonian, France.