PLATE 34. 
Figs. 1 - 23. Spirifera mucronata. 
1, 2, 4. Dorsal valves, showing variations in the extension of the cardinal extremity. 
3. Ventral valve of a specimen from the Marcellus shales, very much extended on the hinge line. 
5, 6, 7. Dorsal, ventral and profile views of a specimen of medium size and ordinary form. 
8. Dorsal view of a specimen in which the hinge line is not extended. 
9. Dorsal view of a specimen which is extended on the hinge-line, so as to give a triangular form to 
the shell. 
10. Dorsal yiew of an individual, having a semicircular outline. 
11. Ventral view of a large and well preserved individual of ordinary form, showing a 
deeply impressed line on the mesial fold, with a corresponding plication in the sinus. 
12. Dorsal view of the above. 
13. Profile of the same. 
14. Cardinal view of the same. 
15. Ventral view of a specimen where the hinge-line is considerably extended. 
16. Dorsal view of a specimen from the arenaceous shales, in which the cardinal extremities are 
greatly extended. 
17. Ventral view of another specimen of the same character. 
18. Front view of a specimen of ordinary form. 
19. Ventral view of a short gibbous form with an angular mesial fold and sinus. This form 
approaches in character, S. ziczac. 
20. Dorsal view of same. 
21. Front view of same. 
22. Interior of ventral valve. 
23. Interior of dorsal valve. 
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