PLATE XL. 
Fenestella (Polypora) quadrangularis. 
Page 158. 
See Plates 35 and 36. 
Fig. 1. A lateral view of a branch. (X 6.) 
Fig. 2. A portion of the non-celluliferous face of a frond, distinctly showing the carinse of the branches 
and dissepiments, and the nodes opposite the dissepiments. (X 6.) 
Upper Helderberg group. Falls of the Ohio river. 
Fenestella (Polypora) submutans. 
Page 167. 
Fig. 3. A portion of the non-celluliferous face of a frond, natural size. 
Fig. 4. A portion of the preceding, showing comparatively regular branches, with dissepiments nearly 
equal in width to the branches. (X 6.) 
Fig. 5. Another part of the same, showing more irregular branches and proportionally narrower dissepi¬ 
ments. (X 6.) 
Upper Helderberg group. Falls of the Ohio river. 
Fenestella (Polypora) aculeata. 
Page 157. 
See Plate 35. 
A portion of the non-celluliferous face of a frond, natural size. 
An enlargement of a portion of the non-celluliferous face. (X 6.) 
An enlargement from another frond, having stronger branches, wider, dissepiments, and more 
numerous and prominent nodes. The fenestrules over a portion of the specimen are also more 
broadly oval. (X 6.) 
Transverse section of the branches of fig. 10, showing their form and the interior space occupied 
by the cells. (X 6.) 
A portion of the celluliferous face of a frond, showing the carinate branches and dissepiments, 
with nodes on the carinse of the branches. (X 6.) 
A lateral view of one of the branches of fig. 10, showing the node-like spines on both the cellu¬ 
liferous and non-celluliferous faces. (X 6.) 
Upper Helderberg group. Falls of the Ohio river. 
Fenestella (Polypora) brevisulcata. 
Page 168. 
Fig. 12. The non-celluliferous face of a frond, natural size. 
Figs. 13, 14, 15. Enlargements of different portions of fig. 12, showing the comparative size and character 
of the branches and dissepiments. (X 6.) 
Upper Helderberg group. Walpole, Ontario, Canada. 
Fenestella (Polypora) striatopora. 
Page 168. 
Fig. 16. Transverse section of the branches of fig. 17, showing their form and the space occupied by the 
cells. (X 6.) 
Fig. 17. An enlargement of a portion of the non-celluliferous face of a frond, showing the comparative 
size and character of the branches and dissepiments. (X 6.) 
Fig. 18. An enlargement of a portion of the celluliferous face of a frond where the elevated margins of 
one side of the cell apertures are very strongly developed. (X 6.) 
Fig. 19. An enlargement from another portion of the same frond, showing the margins of the cell 
apertures more equally developed. (X 6.) 
Upper Helderberg group. Falls of the Ohio river. 
Fig. 6. 
Fig. 7. 
Fig. 8. 
Fig. 9. 
Fig. 10. 
Fig. 11. 
