1a.Primary ambulacral tubercles (on left) almost as large as interambulacral tubercles (on right) at ambitus. |
1b.Primary ambulacral tubercles (on left) always very much smaller than interambulacral tubercles. |
2a.Aboral interambulacral plates devoid of primary tubercles. |
2b. Aboral interambulacral plates with fully developed primary tubercles. |
3a. Ambital ambulacral tubercles overlapping three elements; pore-pairs forming phyllodes adorally. |
3b. Primary ambulacral tubercles minute and confined to single element; phyllodes weakly developed. |