PLATE 27. 
Figs. 1-4. CYRTINA, HAMILTONENSIS.. 
1, 2. Views of casts of a dorsal and a ventral valve, from the Schoharie grit, the latter 
showing the line of the medium septum. 
3, 4. Front and cardinal views of a ventral valve from the Corniferous limestone, the latter 
view showing the covered deltidium. 
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Figs. 5 - 10. Cyrtina biplicata. 266 
* 5, 6, 7. Dorsal, cardinal and front views of an individual of this species, from tlite Schoharie grit. 
8. A ventral valve of a specimen from Michigan. 
9, 10. Ventral and cardinal views of the original specimen of this species. 
Figf. 11-12. Cyrtina crassa.... ? 267 
11, 12. Dorsal and ventral views of a specimen of this species from the Corniferous limestone. 
Figs. 13 - 16. Spirifera duodenaria. ..... 189 
13. A young individual, which is a partial cast. 
14. A ventral valve of this species. 
15. The cast of a dorsal valve. 
16. The cast of a ventral valve. These specimens are all from the Schoharie grit. 
Figs. 17-28. Spirifera macra. 190 
17. A young individual of this species. 
18. A full grown specimen retaining the shell. The extremities are restored from other speci- 
19, 20, 21. Dorsal, cardinal and profile views of a specimen retaining a portion of the shell. 
22. A cast of a large dorsal valve. 
23. A cast of a ventral valve. 
24. A cardinal view of a cast of the ventral valve. 
25. The cast of a ventral valve of a small individual of this species. ? 
26. 27. Dorsal and ventral views of an individual which is less extended on the hinge line than 
the usual form. The specimen is somewhat weathered. 
28. Profile of the above. 
Fig. 29. Spirifera grieri..^... 194 
29. A dorsal view of a crushed specimen, from the Schoharie grit. 
Figs. 30-34. Spirifera raricosta. 192 
30. The ventral valve of an exfoliated shell. 
31. The cast of a dorsal valve, showing the teeth sockets and median septum. 
32. The cast of a ventral valve, showing the muscular impressions, central septum, and filling 
of the rostral cavity. 
33. 34. Ventral views of two young specimens, referred with doubt to this species. 
