The Echinoid Directory

1a. Apical disc tetrabasal.

1b. Apical disc monobasal.

2a. Phyllodes with only two series in each half-ambulacrum. Ambulacra sunken towards the peristome creating swollen pseudobourrelets.

2b. Phyllodes with three series in each half-ambulacrum. Ambulacra not sunken towards the peristome.

3a. Petals straight; gradually expanding distally.

3b. Petals bowed; tapered distally

4a. Periproct marginal.

5a. Peristome distinctly anterior; test ovate.

4b. Peristome central; test circular.

6a. Petals with columns of equal length. Periproct only just inframarginal.

6b. Petals with columns of different lengths. Periproct clearly inframarginal.

7b. Peristome wider than long

8a. Ambulacra raised aborally.

8b. Ambulacra not raised aborally.

9a. Test elongate, cylindrical, with poorly developed phyllodes without a distinct inner series.

9b. Test not cylindrical, with well developed phyllodes that have a distinct inner series.

10a. Marked inequality in the length of the two series of pore-pairs in each petal (except the anterior petal), the shorter pore-series measuring between half to two-thirds of the length of the longer pore-series.

10b. Slight inequality in the length of the two series of pore-pairs in each petal, the shorter pore-series measuring more than two-thirds of the length of the longer pore-series.