PLATE 26. 
Productella hystricula 
Page 
178 
Figs. 1-8. 
I, 2. Impressions of dorsal valves, one of them showing the truncate apex, and both of them 
showing the marks of the narrow linear area. 
3. 4, 5. Casts of ventral valves, the curved lines showing the relative convexity of the speci¬ 
mens. 
6. A restored specimen, showing the spines as preserved in impressions in the sandstone. 
7. The interior of a dorsal valve enlarged to two diameters, showing the form of the cardinal 
process and the small dental sockets. 
8. A cardinal view of a cast of a ventral valve, showing the narrow area and bilobed apex; en¬ 
larged to two diameters. 
Figs. 9-15. Productella costatula. 180 
9. The interior of a dorsal valve, with an enlarged cardinal process from another individual. 
10. A front view of the ventral valve of a narrow individual, showing elongate pustules at the 
bases of the spines, but with no continuous costae. 
II, 12. The front view, and profile of an older individual, showing continuous costae. 
13 - 15. Front view, profile, and cardinal view of another individual, showing continuous costae. 
Figs. 16-23. Productella arctirosTrata . 18^2 
1G, 17. An impression of the exterior of a dorsal valve, with profile of the same. 
18. the impression of a dorsal valve, showing strong concentric wrinkles, with an impression of 
the cardinal process; having fewer pustules on the surface than fig. 16. 
19-21. Front, profile and cardinal views of a ventral valve, of the same variety of form and • 
surface marking, as fig. 16. 
22,23. Two views of the typical specimen of this species; the ventral valve is distorted 
to some extent, but the mesial depression is apparently a natural feature. . 
Figs. 24-28. Productella bialyeata. 183 
24. A small specimen of a ventral valve, showing numerous concentric wrinkles, with a greater 
number of spines towards the front than usual in specimens of this species. 
25. A young individual, with inconspicuous wrinkles, and a well defined mesial sinus. 
26. A larger individual, which is nearly destitute of a sinus. 
27. A larger individual, with distinct wrinkles and spine-bases on the cardinal margin, with a few 
similar marks on one.side, in front; the mesial sinus is but faintly developed. 
28. An imperfect specimen, with faint concentric wrinkles and numerous spiniferous tubercles 
near the front; the sinus is strongly developed. 
Figs. 29-42. Productella onusta. 184 
29. The interior of the dorsal valve of a young individual, showing the cardinal process and 
socket ridges. 
30. The interior of a large dorsal valve, showing concentric wrinkles, the cardinal process and 
median septum, with the muscular and vascular impressions. 
31. The interior of a dorsal valve from which the shell is partially exfoliated; the cardinal pro¬ 
cess is much stronger than in fig. 30. 
32. A cardinal view of the specimen tig. 31, showing the convexity of the inner surface. 
33. A fragment of a large dorsal valve, showing the termination of the reniform vascular impres¬ 
sion on one side, with an oblique vascular impression diverging on each side from the 
termination of the mesial septum. The outline is restored to show the relation of the 
parts preserved. 
34. A dorsal valve which has been doubtfully referred to this species; it is nearly flat, with a 
few obscure wrinkles, and a cardinal process similar to others of this species. 
35. The ventral valve of a young individual. 
36. 37, 38. Ventral and cardinal views, and profile of a large ventral valve of this species. 
39, 40. Cardinal views of casts of two ventral valves, showing the muscular markings, and in 
39, the deep pits on the sides of the beak left by the removal of the dental lamellae. 
41 . An enlargement of the surface of the shell, showing round spine-bases, and irregular lines of 
growth. 
42. An enlargement of the surface of the cast of a ventral valve, showing the irregular striation 
and distant puncta. 
