The Echinoid Directory

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)