PLATE 2—Continued. 
Page 
Figs. 19-22. Discina doria . . 19 
19. Vertical view of a specimen of an tipper valve; enlarged two diameters. 
20. Profile of the same, from Canada West. 
21. A dorsal valve of the same species, natural size. 
22. A group of specimens attached to. a univalve shell. 
Figs. 23, 24. Discina seneca. 20 
23. Vertical view of a dorsal valve, natural size. 
24. Profile of the same. 
Figs. 25-28. Discina media. . . 20 
25. 26. Dorsal and ventral valves, natural size. 
27. A ventral valve enlarged two diameters. 
28. A specimen'of the ventral valve of this species, from the Chemung group. 
Fig. 29. Discina media var . 21 
29. A ventral valve from the Marcellus shale. 
Figs. 30, 31. Discina doria. ?. 21 
30. A vertical view of a dorsal valve, which is rather more convex than usual in this species. 
31. A profile of the same. 
Figs. 32, 33. Discina grandis. 17 
32. A profile showing the usual elevation. The line surrounding this figure gives the ele¬ 
vation of a specimen referred to this species, Plate 1, fig. 18 a. 
33. A fragment of rock with a group of four individuals of this species. 
Fig. 34. Discina randalli. 18 
34. The lower side of a ventral valve, natural size. 
Fig. 35. Discina lodensis.V. 22 
35. A group of three ventral valves, natural size. 
Figs. 36, 37. Discina truncata. 23 
36. 37. Dorsal and ventral valves enlarged to three diameters. 
Figs. 38, 39. Discina elmira. 24 
38. A dorsal valve, vertical view. 
39. Profile of the same. 
40. Undetermined. 
2 
