Plate 23. 



1^. Porocidaris variabilis A. Ag. and Clark. 



1. Abactinal view of partly cleaned, light-colored specimen. 



2. Actinal view of same. 



?>. Ambulacral view of same. 



4. luterambulacral view of same. 



5-8. Aporocidaris fragilis A. Ag. and Clark. 



5. Abactinal view of cleaned test. 



6. Actinal view of same. 



7. luterambulacral view of same. 



8. Ambulacral view of same. 



All figures natural size. 



