The Echinoid Directory

• Test hemispherical, flattened beneath.
• Apical disc small, less than one-quarter test diameter; plating dicyclic, with posterior oculars closer to periproct than anterior oculars. Genital plates large, with one or two large tubercles. Periproct with smooth edges.
• Ambulacra narrow, slightly sinuous above. Plating trigeminate aborally, quadrigeminate at ambitus; compounded in diadematid style with all elements extending to perradius. Pore-pairs uniserial above and at ambitus, expanded adorally to form phyllodes. Primary tubercles large on oral surface, sharply decreasing in size at ambitus but continuing to apex.
• Interambulacral plates a little wider than tall, dominated by a large primary tubercle. Ring of small secondaries surrounds each tubercle forming a scrobicular circle. The top two or three plates with primary tubercle very much reduced - not much larger than scoribicular tubercles, these plates also taller than wide.
• Primary tubercles at ambitus and adorally with small, rudimentary perforate and with feeble crenulation only on their adoral side. On the aboral surface tubercles imperforate and non-crenulate. Those of the ambulacra very much smaller than those of the interambulacra.
• Peristome large, more or less flush, with deep, open buccal notches giving the peristome edge a crenulate appearance.
• No sphaeridial pits and no basicoronal interambulacral plate in adult.
• Spines and lantern not known for certain.

Middle to Upper Jurassic (Bajocian-Oxfordian), Europe.

A species of Acrocidaris