Clark. — The Cidaiidae. 



PLATE 6. 



1-2. Tretocidaris perplexa, 6p. nov. Nat. size. 



1. Abactinal view. 



2. Actinal view. 



3-4. Tretocidaris dubia, sp. nov. Nat. size. 



3. Abactinal view of partly cleaned specimen. 



4. Actinal view of same. 



