The Echinoid Directory

• Test tall, hemispherical, flattened beneath, domed above.
• Apical disc small, about one-third test diameter; plating hemicyclic with the posterior oculars exsert. Genital plates large, hexagonal, G2 generally the largest. Periproct ovate with slightly angular edges.
• Ambulacra narrow, straight. Plating simple from the ambitus adapically, with small marginal tubercle (imperforate and non-crenulate) on each element, the broad perradial zone being densely covered in granules. Sharp change at ambitus to plates with large primary tubercle; plating polygeminate at ambitus, trigeminate adorally. Compounded in diadematid style, with all elements extending to perradius. Pore-pairs uniserial above and at ambitus, expanded adorally to form phyllodes.
• Interambulacral plates a little wider than tall, dominated by a large primary tubercle. Narrow band of small secondaries and granules interradially and adradially. Adapical most plates with reduced tubercle.
• Primary tubercles perforate and crenulate. Those of the ambulacra much smaller than those of the interambulacra.
• Peristome large, more or less flush, with deep open buccal notches giving the peristome edge a crenulate appearance. Buccal notches with prominent tag.
• No sphaeridial pits and no basicoronal plate.
• Lantern and spines unknown.

Upper Jurassic, Europe, North Africa.

Hemicidaris alpina Agassiz, 1840, p. 52, by subsequent designation of Lambert & Thiery, 1910, p. 168.

• P. alpina (Agassiz, 1840); Kimmeridgian, Europe.
• P. durandi (Peron & Gauthier, 1876; Kimmeridgian, Algeria
• maybe others

Carinacea, Hemicidaridae, Pseudocidarinae

Monotypic.

The broad, straight  ambulacral zones above the ambitus which are simple and with only a small marginal primary tubercle to each element, readily distinguishes this taxon from Hemicidaris.

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, Aldolphe Jourdan, Alger, 131 pp.