The Echinoid Directory

Key to genera of Echinoida (5)

22a.Pore-pairs offset horizontally so as to form distinct vertical series.

Hemicentrotus

22b.Pore-pairs in arcs, not offset as clearly separated series

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23a.Interambulacral plates with a horizontal row of subequal tubercles at ambitus.

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23b.Interambulacral plates with a distinctly enlarged primary tubercle at ambitus.

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24a.In profile flat-topped with ambitus of test above mid-height.

Echinostrephus

24b.In profile, subconical with ambitus below mid-height.

Pachechinus

25a.Pore-pairs in near vertical arcs; interambulacral plates rather bare.

Polyechinus

25b.Pore-pairs in subhorizontal arcs; interambulacral plates densely tuberculate.

Caenocentrotus