The Echinoid Directory

Contributed by Andrew Smith

Orthocidaris Cotteau, 1862, p. 182, 364

[non Orthocidaris A. Agassiz, 1863, p. 17 [= objective junior synonym of Cidaris Leske, 1778, p. 74]. ]

Diagnostic Features
  • Test large and globular.
  • Apical disc about one-quarter of test diameter with relatively large periproct. Plating dicyclic with large genital plates and small exsert oculars.  Five gonopores. Periproct rim circular, not angular.
  • Ambulacra narrow and straight throughout. Plating  simple aborally with each plate bearing a circumflexed pore-pair; the two pores being somewhat elongate.  Adorally every other plate enlarged adradially so as to exclude the smaller alternate plate. Each bearing a pore-pair - these pore-pairs offset to form a double series in each half ambulacrum.  The perradial zone of each plate bearing a single row of three or four small tubercles.  No primary tubercles overlapping plate sutures.
  • Interambulacral plates large and mostly covered with fine dense granulation.  Each bears a single primary tubercle which occupies only a small part of the plate height.  Primary tubercles are perforate and non-crenulate.
  • Peristome small, not much larger than apical disc, and slightly sunken. No buccal notches.
  • Lantern supports, lantern and spines unknown.
Distribution Lower Cretaceous (Valanginian); France.
Name gender feminine
Type Hemicidaris inermis Gras, 1848, p. 17, by monotypy.  Holotype and only known specimen University of Lyon EM12130.
Species Included Only the type species.
Classification and/or Status Euechinoidea, Acroechinoidea, ?Pedinoida.

Remarks Very similar to Mesodiadema but differing in having  a much smaller apical disc.  Possible represents a link between the Irregularia and the Pedinoida

Cotteau, G. 1862-1867. Paleontologie francaise. Terain Cretace, Tome 7. Echinides. Victor Mason et fils, Paris.