PLATE 19 



Page 

 Figs. 1-5. Strophodonta cayuta 110 



1. A cast of a small ventral raWe. 



2. The more common and prevailing form among specimens of larger dimensions. 



3. A ventral cast, which is very gibbous and aub-plicate in the middle, with the cardinal extremi- 



ties greatly extended. 



4. An enlargement of the surface striae, as shown in an impression in the stone. 



5. An enlargement of the ventral muscular impression, and a part of the cardinal line, to show 



the crenulations 



Figs. 6, 7. Strophodonta ccelata 112 



6. An impression in a fine sandstone preserving the marks of muscular impressions, etc. 



7. The iapression of a convex dorsal valve supposed to be of the same species. 



Figs. 8 - 12. Strophodonta dkmissa 114 



8. 9, 10. Casts of ventral valves, of variable and somewhat distorted forms. 



11. The cast of a ventral valve of the ordinary form of the species. 



12. The cardinal view of the same. 



Figs. 13 - 16. Strophodonta perplana, var. nervosa 113 



13. The interior of a ventral valve having the form and general aspect of S. perplana, but with 



the fine striae characteristic of S. nervosa. 



14. A specimen having the cardinal extremities greatly produced. This specimen is the origi- 



nal of i'. nervoia 



15. A portion of a large ventral valve with sharp, strong, undulating striae, which are some- 



times elevated into pustules and again abruptly depressed. This character of surfaca 

 prevails in all the specimens in certain beds of the rock. 



16. An enlargement of a part of the surface of the preceding specimen, showing the peculiar 



features of the striae. 

 17, 18, 19. These specimens are casts of the ordinary forms of the S. ptrplana = S.delthyrU 

 (Conrad), as it occurs in the Chemung group. 



