The Echinoid Directory

Gomphechinus Pomel, 1883, p. 90

Diagnostic Features	Test wheel-shaped, flattened below and above. Apical disc pentagonal, moderately large; plating not firmly bound to corona; always lost. Ambulacra polygeminate, 5 or 6 elements in a compound plate at ambitus and above, 4 adorally. Plate compounding stomopneustid-style with middle element the largest and reaching the perradial suture, highest and lowest elements also reaching the perradius, with small ocluded plates in between. Pore-pairs arranged biserially above the ambitus and adorally; becoming approximately uniserial at the ambitus. Ambulacral plates with single large tubercle; little perradial space Interambulacral plates much wider than tall, slightly flexed. Two subequal primary tubercles on ambital plates plates the interradial one lost adapically; sometimes a third smaller tubercle adradially on subambital plates. Ambulacral and interambulacral tubercles of similar size. No aboral naked interradial zone. Primary tubercles imperforate and non-crenulate; mamelon rather massive. Peristome large, a little sunken; buccal notches small but sharp. Spines and lantern unknown; no primordial interambulacral plate.
Distribution	Upper Cretaceous, South America, North Africa, Madagascar.
Name gender	masculine
Type	Leiosoma selim Peron & Gauthier, 1881, p. 141, by monotypy.
Species Included	G. selim (Peron & Gauthier, 1881); Campanian-Maastrichtian, North Africa. G. parahybensis (Maury, 1930); Campanian-Maastrichtian, Brasil. G. collignoni Lambert, 1933; Maastrichtian, Madagascar.
Classification and/or Status	Euechinoidea, Calycina, Phymosomatoida, unnamed taxon.
Remarks	The large apical disc is very reminiscent of Phymosomatidae, but the ambulacral plate compounding is different. Close to Plistophyma, but without the distinct shortening of interambulacral plates at the ambitus, and with two subequal primary tubercles on ambital interambulacral plates, not one. Pomel, A. 1883. Classification méthodique et Genera des Échinides vivante et fossiles. Thèses présentées a la Faculté des Sciences de Paris pour obtenir le Grade de Docteur ès Sciences Naturelles 503, Aldolphe Jourdan, Alger, 131 pp. Smith, A. B. & Jeffery, C. H. 2000. Maastrichtian and Palaeocene Echinoids: a key to world faunas. Special Papers in Palaeontology 63, 1-404.