The Echinoid Directory

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Key to the genera of Palaeotropidae

1a. Ambulacral pores double in paired ambulacra aborally. Go to 3	1b. Ambulacral pores minute and single throughout. Go to 2
2a. Ambulacral plating biserial adapically. Paleotrema	2b. Ambulacral plating uniserial adapically. Palaeotropus
3a. Ambulacra becoming uniserial adapically. Scrippsechinus	3b. Ambulacra remain biserial to apex. Go to 4
4a. Labral plate relatively short and bearing spines; apical disc with only two large gonopores (sometimes with two smaller anterior gonopores). Palaeobrissus	4b. Labral plate relatively long and without spines; apical disc with four large gonopores . Acanthotrema