The Echinoid Directory

• Test plating rather thin, although effectively sutured throughout.
• Apical disc unknown (plating lost from all specimens); opening relatively large. Genital plates not indenting corona strongly.
  
• Ambulacral straight; about one-third of interambulacral width; pore-pairs non-conjugate; uniserial adapically, biserial at ambitus and expanded adorally into phyllodes.
• Ambulacral plating pseudocompound with single large primary tubercle on every second or third plate and with small plates occluded from adradial or interradial sutures.
• Interambulacral zone with ambital plates pentagonal and only a little wider than tall.
• One large primary tubercle on each interambulacral plate; all tubercles perforate and with depressed areole; mamelon small. Small secondary tubercles confined to plate edge. Impossible to tell for certain whether tubercles are crenulate or non-crenulate from specimen.
• Peristome with deep, rather sharp buccal notches.
• Spines unknown.

Middle Jurassic (Callovian) of France, Late Jurassic, (?Oxfordian; Weissser Jura) of Germany.

Pedinothuria cidaroides Gregory, 1897, by original designation.

• Only the type species.

Euechinoidea; Acroechinoidea; Incertae sedis.

Monotypic.

The relationship of this genus within the Acroechinoidea is problematic, although it clearly is rather basal within that group. It most resembles the Micropygoida in having deep, sharp, buccal notches and a biserial arrangement of ambulacral pores. However, the detailed style of ambulacral plate compounding is different, and there is only a single primary tubercle to each interambulacral plate. It differs from members of the Diadematoida in having deep and sharp buccal notches and a large rounded apical disc like that of Aspidodiadematidae. Like Aspidodiadematoida it also has very similar interambulacral tuberculation and plating. However, its biserial arrangement of pore-pairs immediately distinguishes it from aspidodiadematoids. Without better perserved material it will be impossible to be more specific about the placement of this genus.

Gregory, J. W. 1897. On the affinities of the Echinothuridae, and on Pedinothuria and Helikodiadema, two genera of Echinoidea. Quarterly Journal of the Geological Society, London 53, 112-122.

Mortensen, T. 1940. A monograph of the Echinoidea. Volume III. 1, Aulodonta. C.A. Reitzel, Copenhagen.

Vadet, A., Nicolleau, P. & Pineau, J. P. 1996. Echinides du Callovien de la Sarthe et de l'Orne II-A: les echinides reguliers. Memoires de la Societe Academique du Boulonnais, Serie Histoire Naturelle 17, 184 pp., 29 pls.