PLATE LII. 



Figure 1. Echinodiscus placenta, Duncan and Sladen (page 329). Abactinal viev, natural 

 size. 



2. The apical disk, magnified. 



3. Part of an ambulacrum, magnified. 



4. Echinodiscus, sp. (page 331) . Part of the test^ abactinal view, natural size; 



5. Actinal view of the same specimen. 



6. Part of the same magnified, showing the ambulacra near the peristome. 



7. Surface of a test, showing the tops of the supporting structures. 



8. Echinodiscus placenta, Duncan and Sladen. A portion of an ambulacrum and 



lunule, slightly magnified^ 



