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. Monotypic.
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.