Plate 6. 



1-17. Stereocidaris leucacantha A. Ag. and Clark. 



1. Tridentate pedicellaria. x 55. 



2. Smaller tridentate pedicellaria. x 55. 



3. Globiferous pedicellaria. x 55. 



4. Small globiferous pedicellaria. x 156. 



5. Valve of tridentate pedicellaria. x 55. 



G. Valve of globiferous pedicellaria. x 156. 



7. Calcareous particles from pedicels, x 156. 



8. Ambital primary spine. Nat. size. 



9. Base of same spine, x 5. 



10. Tip of same spine, x 5. 



11. End view of same tip. x 5. 



12. Actinal primary spine, x 5. 



13. Smallest actinal primary spine, x 11. 



14. Interambulacral secondary si^ine. x 11. 



15. Ambulacral secondary spine, x 23. 



16. Actinal secondaries, x 23. 



17. Miliaries. x 23. 



