PLATE XXXVIII. 
Fenestella (Polypora) porosa. 
Page 163. 
1. The non-celluliferous side of a specimen, natural size, showing considerable variation in the size 
of the branches on different portions of the frond. 
2. Another specimen, natural size, the branches being nearly uniform and smaller than those of fig. 1. 
3. The celluliferous side of a specimen, natural size. 
4. An enlargement of a portion of fig. 1, showing more distinctly the variation in the size of the 
branches, and the character of the branches and dissepiments. (X 6.) 
5. An enlargement of a portion of fig. 2. It varies from fig. 4 in having the fenestrules larger and 
much wider than the branches; the branches are more angular and occasionally sub-carinated. 
(X 6.) 
6. An enlargement of a portion of fig. 3, showing the fenestrules narrower than on the non-cellulife- 
rous side, the carinated dissepiments and the form and arrangement of the cell apertures. 
(X 6.) 
Upper Helderberg group. Walpole, Ontario, Canada. 
' 1 
Fenestella (Polypora) perundata. 
Page 163. 
7. A portion of the non-celluliferous face of a frond, natural size ; the branches over a portion of the 
frond are quite regularly arranged and united by anastomosis. 
8. A portion of the non-celluliferous face of another frond, in which the branches are more irregular 
than those of fig. 7. 
9. A portion of the celluliferous face of a frond, showing the size of the branches and their manner 
of growth. 
10. An enlargement of a portion of fig - . 7, showing more distinctly the character of the branches and 
their connection by anastomosis. (X 6.) 
11. An enlargement of a portion of fig. 8; the branches are narrower than those of fig. 10, usually 
rounded ; the fenestrules, in proportion to the branches, are much wider. (X 6.) 
12. An enlargement of a portion of fig. 9, showing the regularly sinuous form of the branches," and 
the form and arrangement of the cell apertures. (X 6.) 
13. An enlargement of a portion of two branches of the celluliferous face of a frond, showing the 
triangular non-celluliferous space immediately below the bifurcations, which extends down¬ 
ward between the central ranges of cell apertures, in the form of a narrow groove. 
Upper Helderberg group. Walpole, Ontario, Canada. 
Fenestella (Polypora) hexagonalis. 
Page 161. 
14. A portion of the non-celluliferous face of a specimen, showing the size of the branches and dis¬ 
sepiments, and their manner of growth. 
15. A portion of the celluliferous face of a frond, natural size, showing the regularly sinuous form of 
the branches. 
16. An enlargement of a portion of the non-celluliferous face of a macerated frond, the branches 
having lost their angularity, and presenting simply a rounded form. 
17. An enlargement of a portion of fig. 14, showing more distinctly the character of the branches and 
dissepiments and their comparative size. (X 6.) 
18. An enlargement of a portion of the non-celluliferous face of a frond. The branches and dissepi¬ 
ments are partially imbedded in the rock, which gives to them the appearance of being nar¬ 
rower than they really are. (X 6.) 
19. An enlargement of a portion of fig. 15, showing more distinctly the regularly sinuous form of the 
branches, and the form and arrangement of the cell apertures. (X 6.) 
20. An enlargement of a portion of the surface of another frond, showing, immediately below the 
bifurcations, the triangular non-celluliferous space continued downward between the central 
ranges of cell apertures in the form of a narrow groove. Compared with fig. 19, the branches 
of this specimen are wider, not angular; the fenestrules are longer and narrower. 
Upper Helderberg group. Walpole, Ontario, Canada. 
