PLATE 19 
Page 
Figs. 1-5. Strophodonta cayuta. . 110 
1. A cast of a small ventral valve. 
2. The more common and prevailing form among specimens of larger dimensions. 
3. A ventral cast, which is very gibbous and sub-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 impression of a convex dorsal valve supposed to he of the same species. 
Figs. 8-12. Strophodonta demissa. ...;. 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 S. nervosa 
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 surface 
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. perplana = S. delthyris 
(Conrad), as it occurs in the Chemung group. 
