The Echinoid Directory

• Test low domal in profile with ambitus below mid-height.
• Apical disc hemicyclic, ocular plate III insert, posterior four ocular plates generally exsert. Periproct ovate with smooth margin.
• Ambulacra polygeminate; pore-pairs biserially arranged more or less throughout, with crowding close to the peristome forming phyllodes. Plate compounding style unknown but with many elements reaching the perradius adapically. Large primary tubercle on every compound plate; primary tubercles alternating with small granules in column.
• Interambulacral plates wider than tall, each dominated by a large primary tubercle. Small flanking secondary tubercles on plates below the ambitus. Rest of plate with rather coarse scattered heterogeneous tubercles.
• No aboral naked interradial zone.
• Primary tubercles imperforate and non-crenulate.
• Peristome large; buccal notches sharp and deep.
• Spines and lantern unknown.

Upper Cretaceous (upper Senonian), Germany.

Alternechinus cretaceus Schluter, 1870, p. 62, by monotypy.

• Only the type species.

Euechinoidea, Echinacea, Stomopneustoida, Stomopneustidae

Monotypic; subjective junior synonym of Phymechinus Desor, 1856

Schluter, C. 1883. Die Regularen Echiniden der norddeutschen Kreide. !, Glyphostoma. Abhandlungen zur geologischen Specialkarte von Preussen 4(1), 1-72, pls 1-7.