PLATE 23. 
Page 
Figs. 1-3, 9- 11. Productella navicella. 15(J 
1, 2. Ventral views of two individuals, from the Corniferous limestone. 
3. Profile view of specimen fig. 1. 
9 - 11. Dorsal, ventral and profile views of a more elongated specimen, from the Hamilton 
group. 
Figs. 4, 5. Productella subaculeata?. 154 
4. Ventral valve of a specimen, from the Falls of the Ohio, showing spine-bases and One long spine. 
5. Interior of a dorsal valve of a similar character, from East Victor, New York. 
Figs. 6-8. Productella spinulicosta ?=P. shumardiana . 160 
6. 7, 8. Ventral, profile and cardinal views of a specimen from the Corniferous limestone near 
Louisville, Ky. 
Figs. 12-24. Productella truncata. 160 
12. Interior of a dorsal valve, enlarged to two diameters, from the Marcellus shale. 
13. An enlargement of a portion of the interior of a dorsal valve, showing the cardinal process. 
14. An impression of the exterior of the dorsal valve, showing the area of both valves. 
15. View of a ventral valve preserving several of the spines; from the Marcellus shale. 
16. The exterior of a dorsal valve, from the limestones of the Marcellus shales. 
17. A ventral valve, of small size, having the beak but slightly truncated. 
18. 19, 20. Ventral, cardinal and profile views of a small individual, having a large truncation; 
from the limestones of the Marcellus shales, enlarged to three diameters. 
21, 22. Interiors of dorsal valves. 
23. An impression of the dorsal valve, and the area and beak of the ventral valve, showing a 
narrow deltidium. 
24. A ventral view of a specimen which is somewhat largely truncate. Figs. 21 -24, are from 
specimens from the Hamilton group. Figs. 12, 14-17, 21-23, are enlarged to two 
diui/ieters; fig. 13 to six diameters, and fig. 24 to three diameters. 
Figs. 25-34. (35-37). Productella spinulicosta. 160 
(All the figures of natural size except fig. 26.) 
2.5. The interior of a dorsal valve. 
26. An enlargement of a portion of the above to three diameters to show the cardinal process. 
27. A ventral valve of a small broad form. 
28. Ventral view of an individual of larger size. 
29., Profile of the same. 
30. Cardinal view of the same. 
31. A smaller individual imbedded in the rock, and showing spines attached. 
32. Protile view of a specimen from the Tully limestone; probably of this species. 
33. Caidinal view of the same. 
34. A fragment of shale with crushed specimens of this species, preserving the slender spines. 
_ 35. A ventral view of a specimen from the limestone of the Marcellus shale, which closely 
resembles the P. shumardiana. from the calcareous bands below the Burlington limestone. 
36.. Ventral view of a specimen of P. shumardiana , from Burlington, Iowa. 
37. Profile of the same. 
Figs. 38.^40. Productella bumosa. 162 
38. Ventral view of a small specimen. 
39. Profile of the same. 
40. Ventral view of a larger specimen, showing the base of spines remaining, and the pustules 
becoming elongated and assuming the form of costae. The specimen is a little crushed. 
Figs. 41-44. Productella tullia... 164 
41. An impression of the exterior of a dorsal valve preserving the cardinal process; from the 
Hamilton group. 
42. A dorsal valve of larger size; from the shale of the Hamilton group.. 
43. A large dorsal valve from the Tully limestone. 
44. An enlargement of the pustules and surface striae, as shown in.figs.. 41 & 42. 
Figs. 45 y 46. • Productella exanthemata. 163 
45, 46. The interiors of the dorsal valves of two individuals, natural size. 
Figs. 47, 48. Productella sp ?. 165 
47. The interior of a dorsal valve, natural size. » 
48. A profile of the same. 
Fig. 49. Productella subalata. 165 
49. Ventral view of an individual, from the calcareous shale at Hock Island, Illinois. 
