The Echinoid Directory

• Test small and depressed, flattened above and below.
• Apical disc large, subcircular, more than half test diameter; plating caducous.
• Ambulacra straight, tapered rather strongly both adapically and adorally; plating trigeminate; pore-pairs small, oblique, widely separated on ambital plates but more closely spaced adorally and adapically; uniserial throughout - with almost no phyllodes.
• Primary ambulacral tubercle to each plate, largest at ambitus where it covers all three elements, greatly reduced in size adorally and adapically.
• Interambulacral plates a little wider than tall, dominated by a primary tubercle; largest at ambitus. A few secondaries around edges of plate.
• Ambulacral and interambulacral tubercles similar in size; perforate and crenulate.
• Peristome large (but smaller than apical disc), more or less circular; buccal notches extremely feeble, but with thickened rim.
• Spines and lantern unknown.

Upper Jurassic (Oxfordian), France.

Pseudodiadema langi Desor, 1856, p. 65, by monotypy.

Only the type species.

Euechinoidea, Calycina, Phymosomatoida, Emiiratiidae

Monotypic; subjective junior synonym of Polydiadema Lambert, 1888.

Supposedly differing from Trochotiara by its lack of buccal notches. However, buccal notches, though small, are definitely present, and there is nothing of sugnificance to distinguish Aplodiadema from Trochotiara and Polydiadema. The specimens illustrated here are from the Lambert and de Loriol collections. Lambert & Thiery (1911, p. 184) wrongly listed this as Tithonian; it is Oxfordian.

There are three specimens of langi in the de Loriol collection, presumably the material on which the genus was based.

de Loriol, P. 1903. Notes pour servir a l'etude des Echinodermes. Series 2, Part 1. Bale, Georg. [published January, 1903]