The Echinoid Directory

5a. Periproct on near vertical posterior face. Plastron plating continuous. Subanal fasciole present.

5b. Periproct inframarginal. Plastron plating disjunct. No subanal fasciole.

Go to 6

6a. Test triangular in outline (anterior to right). Posterior ambulacral zones continuous on oral surface.

6b. Test ovate in outline (anterior to top). Posterior ambulacral zones disjunct on oral surface, separated by plates of interambulacra 1 and 4 meeting centrally.

7a. Test with strongly keeled plastron to rear.

7b. Test without subanal bulge at rear of plastron.