PLATE IX. 



Strongylocentrotus Drbbachiensis. 



1. Young specimen immediately after resorption of Pluteus, greatly magnified, abacti- 



nal side. 



2. Specimen somewhat older, denuded (actinal side). 



3. Abactinal view of young, having from 5 to 6 plates, magnified |. 



4. Same from actinal side. 



5. Same, magnified portion of ambulacral and interarabulacral space. 



6. Abactinal system of young, measuring SM""- in diam. 



7. Same specimen from the actinal side. 



8. Abactinal view of specimen measuring 5.4°"°- in diam. 



9. Magnified portion of test of same specimen. 



10. Actinal view of same. 



11. Abactinal view of specimen measuring 8.2°™. in diam. 



12. The same seen from actinal side. 



