PLATE XXXIX. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig- 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
V 
Fenestella (Polypora) robusta. 
Page 156. 
See Plates 34, 37 and 46. 
1. A specimen, natural size, showing angular branches and dissepiments. 
2. An enlargement of a portion of the non-celluliferous face of a macerated frond, showing the 
texture of the solid portion of the branches. The lower portion of one of the branches is still 
further worn away, showing the bases of the polygonal cells. 
3. An enlargement of a portion of fig. 1, showing more distinctly the character of the branches and 
dissepiments, when in their natural condition. 
Upper Helderberg group. Walpole, Ontario, Canada. 
Fenestella (Polypora) nexa. 
Page 165. 
4. A portion of the non-celluliferous face of a frond, showing the size of branches and dissepi¬ 
ments, and their manner of growth. 
5. A portion of the celluliferons face of a frond, natural size. 
6. A portion of the non-celluliferous face of a frond, enlarged,, showing angular branches, narrow 
dissepiments, and strong striations on two of the branches. (X 6.) 
7. An enlargement of a portion of fig. 4. The branches are regularly rounded, and slightly nar¬ 
rower than the fenestrules. (X 6.) 
8. An enlargement of the upper portion of fig. 4. The branches are very irregular, rounded, or 
carinated, and frecpiently less than one-half the width of the fenestrules. (X 6.) 
9. An enlargement of a portion of fig. 5, showing more distinctly the form and comparative size of 
the branches and dissepiments, the form and arrangements of the cell apertures and the lon¬ 
gitudinal stri;e on a portion of one branch. (X 6.) 
Upper Helderberg group. Walpole, Ontario, Canada. 
,(.!) X) .yvii'uiv oil V> m! -.i • •• !.-»/;•(i.(?■> 
Fenestella (PolypoRa) separata. 
Page 166. 
10. The celluliferous side of a specimen, natural size, showing the size of the branches and dissepi¬ 
ments, and their manner of growth. 
11. An enlargement of a portion of fig. 10, showing more distinctly the character of the branches and 
dissepiments, their comparative size; the form and arrangement of cell apertures, and the 
longitudinal striae separating the ranges of apertures. (X 6.) 
Upper Helderberg group. Walpole, Ontario, Canada. 
Fenestella (Polypora) mutabilis. 
Page 166. 
12. A portion of the non-celluliferous face of a frond, natural size. 
13. A portion of fig. 12 enlarged. The branches are strong, wider than the fenestrules, rounded, 
with a narrow carina along the middle. The upper portion of the branches is strongly striated, 
the dissepiments carinated. (X 6.) 
14. An enlargement of another portion of fig. 12; the branches are more irregular than those of 
fig. 13: not so strong and more angular; the dissepiments are angular. (X 6.) 
15. An enlargement of a portion of the celluliferous face of a frond, showing the form and compara¬ 
tive size of the branches and dissepiments, and the form and arrangement of the cell aper¬ 
tures. (X 6.) 
Upper Helderberg group. Walpole, Ontario, Canada. 
