188 EXPLANATION OF THE PLATES. 



frustrule. Fig. 30. A band of several frustrules, 



moderately magnified. 

 Plate IX. — Fig. 31. Zygoceras margaritaceum. 



" Fig. 32. Triceratium gibbosum, Bail. & Harv. ; top 



view. 

 " Fig. 33. Lagena Williamsonii, Bail. & Harv. 



