The Echinoid Directory

• Test hemispherical, flattened beneath, domed above.
• Apical disc small, less than one-third test diameter; plating dicyclic. Genital plates large, hexagonal, G2 generally the largest. Periproct subpentagonal with smooth edges.
• Ambulacra very narrow aborally and sinuous, plating acrosaleniid at ambitus and above, becoming simple close to apex, but with larger tubercle on every third element. At ambitus and adorally plating becomes polygeminate; compounded in diadematid style with all elements extending to perradius. Pore-pairs uniserial aborally and at ambitus, expanded adorally to form phyllodes. Large primary tubercles on oral and ambital plates; arranged alternately rather than biserially at ambitus.
• Interambulacral plates almost as tall as wide, dominated by a large primary tubercle. Only narrow bands of small secondaries and granules around edges of plates.
• Primary tubercles perforate and crenulate. Those of the ambulacra about half the size of those of the interambulacra in the subambital region.
• Peristome large, more or less flush, with well defined buccal notches.
• No sphaeridial pits and no basicoronal interambulacral plate retained as adult.
• Spines long and stout, about 1.5 times test diameter; distally tapering to a point; with smooth cortex.
• Lantern unknown.

Middle to Upper Jurassic (Callovian-Kimmeridgian), Europe.

Hemicidaris stramonium Agassiz, in Agassiz & Desor, 1847, p. **, by subsequent designation of Lambert & Thiery, 1910, p. 170.

• H. stramonium Agassiz, in Agassiz & Desor 1847; Oxfordian-Kimmeridgian, Europe.
• H. merryaca (Cotteau, 1859); Callovian, France.

Euechinoidea, Carinacea, Hemicidaridae, Hemicidarinae.

Monotypic

Distinguishable from Hemicidaris by having massive primary ambulacral tubercles that form a single offset column at the ambitus.

Pomel, A. 1883. Classification méthodique et genera des Échinides vivante et fossiles. Thèses présentées a la Faculté des Sciences de Paris pour obtenir le Grade de Docteur ès Sciences Naturelles, 503, 131 pp. Aldolphe Jourdan, Alger.