PLATE III. 



Platystrophia tricenaria. 

 Page 75. 

 Fig. 1. Horizontal section of a portion, including two of the radii, and show- 

 ing the fibrous non-punctate character of the shell. 



Platystrophia biforata. 

 Page 75. 

 Fig. 2. Showing the fibrous structure of the shell. 



Platystrophia occidentalis. 

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 Fig. 3. Similar to the preceding. 



Platystrophia subquadrata. 



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 Fig. 4. Section showing the fibrous structure of the shell, and the large scat- 

 tered punctse. 



Platystrophia flabella. 

 Page 75. 

 Fig. 5. A section including two of the interradial areas. The lower right 

 hand portion has been cut through to the surface of the shell 

 and shows the concentric striae. 



Orthis perveta. 

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 Fig. 6. Section showing the rows of minute punctae. 



Orthis Clytie. 

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 Fig. 7. Showing the single and double rows of punctae between the fibrous 

 interspaces. 



Orthis elegantula. 

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 Fig. 8. Showing somewhat obscurely the broad rows of punctse. 

 Fig. 9. Horizontal section of the shell through a varix of growth; the punctse 

 are partially obliterated by the action of the crystallization of 

 iron pyrite. 



