The Echinoid Directory

Pseudodiadema Desor, 1855 p. 63

Diagnostic Features
  • Test flattened below and above; ambitus rounded.
  • Apical disc small (less than one-quarter test diameter); rounded; plating dicyclic, the posterior oculars insert; Genital plates pentagonal, G2 distinctly larger. Periproct subangular, plating unknown.
  • Ambulacra straight, plating trigeminate throughout; pore-pairs uniform and undifferentiated; more or less uniserial, except adorally where there are short phyllodes. Primary ambulacral tubercle to each plate; plate compounding acrosaleniid, with all three elements reaching the perradius aborally; all three elements overlapped by the primary tubercle at the ambitus.
  • Interambulacral plates wider than tall; plates with a single large tubercle, centrally placed, flanked by small adradial and interradial secondaries. The adradial band well developed on oral surface. No naked interradial zone adapically.
  • Ambulacral and interambulacral tubercles similar in size; perforate and crenulate.
  • Peristome about half test diameter; buccal notches very deep, giving the peristome a crenulated appearance. No sphaeridial pits.
  • Spines long, subtrigonal in corss-section distally and with ribbed cortex.
  • Lantern stirodont, with keeled teeth.
Upper Jurassic (Oxfordian) to Lower Cretaceous (early Albian) western Europe, Mexico and southern USA.
Name gender neuter
Cidarites pseudodiadema Lamarck, 1816, p. 59, by original designation.
Species Included
  • P. pseudodiadema (Lamarck, 1816); Oxfordian, Europe.
  • P. orbignyanum (Cotteau, 1851); Oxfordian, France, Switzerland
  • P. aguilerai (Maldonado, 1953); Aptian, Mexico, Lower Albian, Texas
  • P. jaccardi Cotteau, 1863; Aptian, France.
Classification and/or Status

Acroechinoidea, CarinaceaPseudodiadematidae.


Distinguished by its small hemicyclic apical disc from all Emiratiidae. Distinguished from Hessotiara by having no sharp decline in the size of ambulacral tubercles on the aboral surface.

Desor, E. 1855-1858. Synopsis ds echinides fossiles. Reinwald, Paris.