The Echinoid Directory

Atactus Pomel, 1883, p. 79

[=Rotulechinus Lambert & Thiery, 1914, p. 253 (objective) ]

Diagnostic Features	Test depressed. Apical disc small, plating unknown. Ambulacra trigeminate with primary tubercle on every second plate; tubercles relatively small, leaving wide perradial zone. Interambulacral plates wide with a median primary tubercle, smaller flanking secondaries and scattered granules. Peristome very large.
Distribution	Pliocene of Rhodes.
Name gender	masculine
Type	Psammechinus fischeri Cotteau, 1876 (non Schiner, 1868) by original designation.
Species Included	Only the type species.
Classification and/or Status	Camarodonta; Echinoida; Echinidae. Monotypic. ?Junior synonym of Echinus Linnaeus, 1758.
Remarks	No specimens are currently available for study and so the placement of this genus remains problematic. The original description is inadequate. However, the figure illustrates 6 pore-pairs to each primary plate and tubercle. It is therefore probable that the ambulacra are composed of triads, with a primary tubercle on every other plate. The large size of its peristome is somewhat suspect and may be incorrectly reconstructed. 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.