The Echinoid Directory

 Crown group echinoids with:

• Test small, interambulacral plates firmly sutured; ambulacral plates imbricate strongly beneath interambulacral plates;
• Apical disc not firmly sutured to corona; only just dicyclic;
• Ambulacral plating compound, often in triads, pore-pairs uniserial adapically, biserial adorally;
• Interambulacral plates with single large primary tubercle that is crenulate and perforate. Adoral plates with an adradial row of secondary tubercles.
• Spines long, stout and without ornament.
• Perignathic girdle well developed, entirely interambulacral in origin; composed of an interradial peg and a pair of adradial flanges.

Middle and Upper Triassic, Europe.

This is a fascinating genus because of its perignathic girdle and ambulacral compounding. The adradial 'auricles' resemble those of euechinoids, but these structures are constructed largely from the interambulacral plates and have minimal ambulacral involvement (in euechinoids the same structures are predominantly ambulacral in origin, with only a small input from interambulacral zones). Hagdorn (1995) gives a detailed description of this taxon.

Hagdorn, H. 1995. Die Seeigel des germanischen oberen Muschelkalks. Geologische und Palaontologische Mitteilungen, Innsbruck 20, 245-281.