PLATE XX P. 



Hemiaster cavernosus, /. 1, 3. 



1. Seen from above. 



2. Same, seen from the actinal side. 



Hemiaster australis, /. 3. 



3. Seen from the abactinal side. 



Tripylus excavatus, /. 4- 



4. Seen from the abactinal pole. 



Metalia sternalis, /. 5 - 9. 



5. Seen from above covered with spines ; young specimen. 



6. Seen from the actinal side denuded. 



7. Same, seen in profile. 



8. Same, seen from the abactinal pole. 



9. Section to show internal structure of the abactinal side. 



(All Figs, natural size.) 



