The Echinoid Directory

Grasia Michelin, 1854, p. 439 (3)

Diagnostic Features	Test elongate depressed ; upper surface with median keel; posterior face oblique. Apical disc disjunct; anterior part close to frontal margin; structure unknown. Posterior ocular plates closer to periproct than to the anterior part of the disc, but not bordering periproct. All five ambulacra flush, narrow and with small, oblique pore-pairs. Ambulacral plates short and densely packed aborally. Periproct tear-drop-shaped; flush and supramarginal on obliquely truncated posterior face. Phyllode structure unknown; apparently not well developed. Peristome subcentral, circular, downward-facing and a little depressed. Plastron plating unknown.
Distribution	Upper Jurassic (Oxfordian), France.
Name gender	feminine
Type	Hyboclypus elongata Gras, 1852, p. 49, by monotypy.
Species Included	Only the type species.
Classification and/or Status	Irregularia, Stem group Atelostomata, incertae sedis. Monotypic.
Remarks	The distinct shape of this form makes the genus instantly identifiable. As all material is in the form of internal moulds in chert, the plating of the apical disc is unknown, and so it is impossible to say whether this form has the elongate collyritid disc or the more compact disasterid disc structure. Michelin, 1854. Revue et Magazin de Zoologie 6, p. 439. Vadet, A. Nicolleau, P. & Pineau, J. P. 1998. Echinides du Callovien de la Sarthe et de l\'Orne. II-B: Les echinides irreguliers. Memoires de la Societe Academique du Boulonnais Serie Histoire Naturelle 19, 1-128, pls 1-40.