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The Echinoid Directory

Family Hemicidaridae Wright, 1857, p. 68

Diagnosis

 Carinacea with:

  • apical disc relatively small; dicyclic to hemicyclic; firmly bound to corona. Periproct subcircular with smooth edges (no intercalated periproctal plates);
  • ambulacra trigeminate to polygeminate, with all elements extending from adradial to perradial suture. Sometimes simple adapically;
  • pore-pairs uniserial at ambitus and above; crowded to form phyllodes adorally;
  • primary tubercles in ambulacral zones significantly smaller than those of interambulacral zones; interambulacral tubercles perforate and usually crenulate;
  • peristome much larger than apical disc; with deep, open buccal notches.
Range
Middle Jurassic to Lower Cretaceous, Europe, North Africa, Middle East, India, Madagascar.
Species Included There are two subfamilies, Hemicidarinae and Pseudocidarinae, included here
Classification and/or Status Euechinoidea, Acroechinoidea, Carinacea
Remarks
Like acrosalenids in having ambulacral tubercles very much smaller than interambulacral tubercles, perforate and crenulate tubercles and acrosaleniid-style plate compounding with all elements extending to the perradius, but differing in having a rounded periproct without angular elements forming an integral part of the apical disc circlet.

Wright, T. 1855-1860. Monograph of the British fossil Echinodermata of the Oolitic formations. I. Echinoidea. Monographs of the Palaeontographical Society. 481 pp.