The Echinoid Directory

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Key to genera of Pseudodiadematidae 1a. Genital plates with single large primary tubercle. Ambulacral plating polygeminate. Acrocidaris 1b. Genital plates with small secondary tubercles at most. Ambulacral plating trigeminate. Go to 2 2a. Ambulacral tubercles show a sharp reduction in size above the ambitus. Hessotiara 2b. Ambulacral tubercles reduce in size gradually above the ambitus. Go to 3 3a. Interambulacral plates with wide zone of small granules in addition to primary tubercle. Apical disc hemicyclic. Stereopyga 3b. Interambulacral tubercles heterogeneous, with intermediate secondaries developed. Apical disc dicyclic. Pseudodiadema