The Echinoid Directory

• Apical disc monocyclic, with ocular and genital plates forming an unbroken circle.
• Ambulacra trigeminate, with a single large element reaching the perradial suture and two small accessory plates positioned centrally and abutting one another. Only becoming adradial in position close to the apex.
• Primary ambulacral tubercle on every second or third principle plate; tubercles perforate and non-crenulate.
• Ambulacra about half the width of interambulacra at the ambitus.
• Interambulacral plates lacking membranous gaps; fully imbricate.
• A single primary interambulacral tubercle on every other plate only; remainder of plate with only sparse granulation. No adradial row of tubercles adorally in interambulacral zones.
• Shallow buccal notches.
• Only ambulacral plates extending over the peristome, with pore-pairs arranged uniserially.
• Spines distally ending in weakly expanded cone-shaped hyaline hoof.

Late Cretaceous (Santonian), UK.

Echinothuria floris Woodward, 1863, by original designation.

• Only the type species is based on sufficient material to be identifiable to species level.

Euechinoidea; Echinothurioida; Echinothuriidae; Echinothuriinae.

Monotypic.

Like Araeosoma, Asthenosoma, Hapalosoma and Calveriosoma in having the pore-pairs arranged as three discrete series, but easily distinguished from those genera by its lack of membranous gaps between plates of the interambulacral series. Closest to Hygrosoma but in that genus the adoral accessory plates become adradial and the pore-pairs form a single series.

Smith, A.B. & Wright, C. W. 1990. British Cretaceous Echinoids. Part 2. Echinothurioida, Diadematoida and Stirodonta (1, Calycina). Palaeontographical Society Monographs 101-198, pls 33-72 (publication no. 583, part of Volume 143).

Woodward, S. P. 1863. On Echinothuria floris, a new and anomalous echinoderm from the Chalk of Kent. The Geologist 6, 327-330.