THE FINER STRUCTURE OF CERTAIN DIATOMS. 271 



Explanation or Plate XVII. 



Fig. 1. Coscinodiseus aster omphalos. Rom. imm. T \ ; N.A., 1*43 X. Per- 

 forated membrane within coarse areolations. 



Fig. 2. Isthmia nervosa. Rom. imm. - x \; N.A., 1"43 X- Perforated 

 membrane within coarse areolations. At lower part of Fig. a fracture is 

 shown passing through the perforations. , 



Fig. 3. Triceratium favns. Rom. imm., &c, &c. Fracture passing 

 through perforations. 



Fig. 4. Eupodiscns argus. Rom. imm., &c, &c. Secondary and tertiary 

 markings on interior membrane seen through coarse areolations of outer 

 membrane. 



Fig. 5. P. angulatiim. Rom. imm., &c, &c. Fracture passing through 

 perforations. 



V 



