The Echinoid Directory

• Test small, flattened below and low domal above.
• Apical disc small, circular, plating dicyclic.
• Ambulacra trigeminate with pore-pairs in arcs of three. Plate compounding diadematoid. Primary tubercle to each compound plate, covering all three elements. Smaller secondary tubercle to the interior.
• Pore-pairs forming arcuate throughout, no phyllodes adorally.
• Interambulacral plates a little wider than tall. A single primary tubercle on each; small secondary tubercles at adradial and interradial edges of plates.
• No aboral naked interradial zone.
• Primary tubercles imperforate and non-crenulate.
• Peristome large, hardly invaginated; buccal notches shallow but distinct.
• Spines and lantern unknown.

Turonian, France.

Leiosoma archiaci Cotteau, 1866, p. 767, by monotypy.

• Only the type species.

Euechinoidea, Camarodonta, Temnopleuroida, ?Trigonocidaridae.

Monotypic; Subjective junior synonym of Circopeltis Pomel, 1883

Originally distinguished from Circopeltis on account of it having trigeminate plate compounding. However, it is likely that Circopeltis also has trigeminate plating (all specimens labelled as C. meridanense in Lambert\'s collection are trigeminate).

Lambert, J. 1897. Note sur quelques échinides Éocènes de l’Aude (I. Endocycles). Bulletin de la Société géologique de France, (3) 25, 483-517, 1 pl.