PLATE 51 



Delthyris missouriensis n. sp. 

 Page 199. 



Figs, 1-6. Posterior, side, and ventral views of two specimens. 



Figs. 7, 8. Posterior and side views. 



Fig. 9. A portion of a ventral valve. 



Fig. 10. Interior of a fragment of a ventral valve. 



Fig. 11. Dorsal view. 



Spirifer cyclopterus Hall 

 Page 200. 



Figs. 12, 13. Ventral and dorsal views. 



Figs. 14-16. Dorsal, ventral, and posterior views. 



Figs. 17-19. Dorsal, ventral, and anterior views. 



Figs. 20, 21. Incomplete dorsal valves. 



Figs. 22, 23. Interior of fragments of ventral valves. 



Fig. 24. Side view. 



Fig. 25. Ventral view. 



Fig. 26. Dorsal view of an incomplete shell on which the medial depression of the fold 



is well-marked, and which has a bifurcated plication. 

 Fig. 27. A portion of a ventral valve. 



Delthyris octocostatus (Hall) ? 

 Page 199. 



Figs. 28, 29. Ventral and dorsal views of the single specimen. 



Cyrtina dalmani (Hall) 

 Page 201. 

 Fig. 30. Posterior view. 

 Fig. 31. Dorsal view. 



