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1a.Internal buttressing comprises radial elements with lateral branches. |
1b.Internal buttressing more complex. |
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2a.Four gonopores; hydropores scattered over surface. |
2b.Five gonopores; hydropores in groove or pit. |
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3a.Periproct situated midlength between peristome and posterior margin (first paired interambulacral plates short). |
3b.Periproct situated close to posterior margin (first paired interambulacral plates greatly elongate). |
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4a.Petals about half the radius. |
4b.Petals extend most of the distance to the ambitus. |
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5a.Periproct bounded by first and second post-basicoronal interambulacral plates. |
5b.Periproct opening posterior to first and second post-basicoronal interambulacral plates. |
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6a. Interambulacral zones only slightly narrower than ambulacral zones at ambitus. |
6b. Interambulacral zones very much narrower than ambulacral zones at ambitus. |