EXPLANATION OF PLATE X. 



(All figures after Clark.) 







PSAMMECHINUS CINGULATUS Clark, P. 



1-3. Dorsal, ventral and lateral views of a complete individual. 



4. Interambulacral area, enlarged. 



5. Three interambulacral plates highly magnified. 



6. Ambulacral area, enlarged. 



7. Four ambulacral plates, highly magnified. 



8. Oral opening, enlarged. 



9. Tubercle, enlarged. 



V'mcento^vn lime sand. 



900 



