The Echinoid Directory
Key to genera of Discoidinae
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1a. Apical disc with one (sometimes two) enlarged genital plates which bear all the madrepores. |
1b. Apical disc with all five genital plates subequal and covered in madrepores. |
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2a. Ambulacral plating complex on oral surface with double column of pore-pairs. |
2b. Ambulacral plating on oral surface composed of relatively simple triads; not forming a double column. |