The Echinoid Directory

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Key to stem group Salenioida genera

1a. Ambulacral plating trigeminate throughout (one primary tubercle to every three pore-pairs) Acrosalenia - Go to 2	1b. Ambulacra with unigeminate plating adapically (one tubercle adjacent to each pore-pair) Metacrosalenia
2a. Apical disc with thin U-shaped genital plate 5; periproct opening Acrosalenia (Milnia)	2b. Posterior genital plate not strongly U-shaped Acrosalenia (Acrosalenia)