The Echinoid Directory

Palaeodiadema Pomel, 1887, p. 318

[=Helikodiadema Gregory, 1896, p. 121 (objective) ]

Diagnostic Features
  • Test plating rather fragile, although plating effectively sutured throughout.
  • Apical disc monocyclic or hemicyclic (no complete discs known).
  • Ambulacral straight; about one-third of interambulacral width.
  • Pore-pairs non-conjugate, in arcs of three; becoming crowded adorally to form small phyllodes.
  • Ambulacral plating trigeminate with single large primary tubercle to each plate.
  • Interambulacral zone wide, with ambital plates distinctly wider than tall.
  • One primary tubercle on ambital plates; all tubercles perforate and crenulate. Smaller secondary tubercles on both adradial and interradial sides.
  • Peristome large, with rather shallow, rounded buccal notches.
  • Spines very long and slender; hollow, with verticillate ornament.
Late Cretaceous (Santonian) of the UK ?Maastrichtian and Danian of western Europe.
Name gender neuter
Pseudodiadema fragile Wiltshire, in Wright, 1882, by original designation.
Species Included
  • Only the type species.
Classification and/or Status

Diadematoida; Diadematidae.

?Subjective junior synonym of Centrostephanus Peters, 1855.


Differs from Centrostephanus in no significant details. The material assigned to this genus from the Maastrichtian of the Maastricht district differs in having prominent secondary tubercles and probably represents a separate species resembling C. rodgersii. However, only fragmentary material of this species is currently known, so detailed comparison with Recent taxa is impossible.

Pomel, A. 1887. Paléontologie ou descriptions des animaux fossiles de l’Algérie: 2, Echinodermes (2 volumes). Publications du Service de la Carte géologique de l’Algérie, 344 pp., 120 pls.

Smith, A. B. & Wright, C. W. 1990. British Cretaceous Echinoidea. Part 2. Echinothurioida, Diadematoida and Stirodonta (1, Calycina). Monographs of the Palaeontographical Society 101-198 (publication 583, part of volume 143).