The Echinoid Directory

Key to genera of Echinoida (6)

26a.Ambulacra with 5 pore-pairs to each plate

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26b.Ambulacra more than five pore-pairs to each plate

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27a.Apical disc dicyclic. (Globiferous pedicellariae without muscular neck).


27b.Apical disc hemicyclic with posterior two ocular plates broadly insert. (Globiferous pedicellariae with muscular neck).

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28a.Ambulacral zones narrow adorally, not as wide as interambulacral zones at peristome edge; test very thin; aboral plates rather naked, with fine granulation in addition to primary tubercles.


28b.Ambulacral zones at peristome broader than ambulacral zones; test robust; aboral plates strongly tuberculate.


29a.Ambulacral zones expanded adorally and wider than interambulacra.


29b.Ambulacral zones uniform in width adorally.

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30a.Apical disc dicyclic.


30b.Apical disc hemicyclic.