PLATE 27. 



Pag* 

 Figs. 1-4. CyRTINA HAMILT0NEN8IS 2 



I, 2. View-s of casts of a dorsal and a ventral valve, from the Schoharie grit, the latter 



showing the line of tlie medium septum. 

 3, 4. Front and cardinal views of a ventral valve ft-ora the Corniferous limestone, the latter 

 view showing the covered deltidium. 



Figs. 5 - 10. Ctrtina biplicata :2(J6 



5, G. 7. Dorsal, cardinal and front views of an individual of this sjiecies, from the Schoharie grit. 



8. A ventral valve of a si)ecimen from Michig.in. 



9, 10. Ventral and cardinal views of the original specimen of this species. 



Figf. 11 - 12. Ctrtina crassa 207 



II, 12. Dorsal and ventral views of a specimen of this species from the Corniferous limestone. 



Fig8. 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 ar* 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 ai-e restored ft'om other spcci- 



mens. 



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 cra.sbcd specimen, from the Schoharie grit. 



Figs. 30-34. Spirifera raricosta 102 



30. The ventral valve of an exfoliated shell. 



31. The ca-st 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 filliiig 



of the rostral cavity. 



33. 34. Ventral views of two young specimens, referred with doubt to this species. 



