The Echinoid Directory

• Test flattened below, gently domed above to flat apical disc.
• Apical disc thick forming raised platform; dicyclic; plates firmly bound to corona. Genital plates pentagonal; gonopore at outer interradial point bounded by interambulacral zones; inner edge sunken forming a periproctal ledge. Ocular plates smaller and projecting. Smooth other than for a single perianal tubercle developed on the inner edge of genital plates and sunken. Periproct relatively small and subpentagonal.
• Ambulacra straight; pore-pairs small, uniserial; distinctly larger on apical surface, the two pores separated by a raised interporal knob; ambulacra expanded orally into phyllodes.
• Ambulacral plating in triads throughout, with goniopygid-style compounding; two unequal elements extending to the perradial suture and united by the primary tubercle plus a third small demiplate in each triad.
• Interambulacral plates a little wider than tall; with a large primary tubercle on each; secondary tubercles and miliary granulation generally sparse and no scrobicular ring. Primary tubercles largest just above ambitus.
• Tubercles imperforate and non-crenulate, with little or no surrounding platform.
• Peristome subcircular, slightly sunken; buccal notches well developed with raised rim; no tag.

Goniopygus major Agassiz, 1838, p. 19, by monotypy.

Echinacea, Arbacioida, Acropeltidae.

Subjective junior synonym of Goniopygus Agassiz, 1838.

Pomel (1883) separated this genus from Goniopygus on account of its five rather than three or four perianal tubercles and because of the abrupt decrease in the size of ambulacral tubercles above the ambitus. Subsequent workers all agree that these differences do not merit generic distinction.

Pomel, A, 1883. 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, 131 pp. Aldolphe Jourdan, Alger.