PLATE XXXIV. 
Fenestella (Polypora) rigida. 
Page 155. 
Fig. 1. A specimen, natural size. 
Fig. 2. An enlargement of a portion of fig. 1, showing the appearance of the non-celluliferous side. 
Fig. 3. An enlargement of a portion of the celluliferous side of a specimen, showing the form and 
arrangement of the cell apertures, and the longitudinal ridges dividing the ranges of cell 
apertures. (X 6.) 
Upper Helderberg group. Near Thompson's lake, Albany eounty, N. Y. 
Fenestella (Polypora) robusta. 
Page 156. 
See Plates 37, 39 and 46. 
Fig. 4. A portion of the non-celluliferous side of a frond, natural size. 
Fig. 5. A portion of the celluliferous side of a frond, enlarged, showing the form and arrangement of 
cell apertures, and comparative size of branches and dissepiments. (X 6.) 
Fig. 6. An enlargement of a portion of the celluliferous side of a frond ; the greater portion of the exterior 
of the branches is broken away, showing the bases of the polygonal cells. (X 6.) 
Fig. 7. An enlargement of the non-celluliferous side of a specimen, showing the form and comparative size 
of branches and dissepiments: the branches of this specimen are narrower than those of the 
frond from which figs. 5 and 6 were made. (X 6.) 
Upper Helderberg group. Walpole, Canada. 
Fenestella (Polypora) largissima. 
Page 156. 
Fig. 8. The non-celluliferous side of a frond,, natural size. 
Fig. 9. An enlargement of a portion of fig. 8, showing the form and comparative size of the non-celluliferous 
face of branches and dissepiments. (X 6.) 
Upper Helderberg group. Central New York. 
Fenestella propria. 
Page 157. 
Fig. 10. A portion of the non-celluliferous face of a frond, natural size. 
Fig. 11. An enlargement of a portion of fig. 10, showing the character of the non-celluliferous face of a 
frond. (X 6.) 
Fig. 12. An enlargement of an impression of the non-celluliferous face of a frond. (X 6.) 
Fig. 13. An enlargement'of a portion of the celluliferous face of a frond, showing the form and arrange¬ 
ment of cell apertures and the carinated dissepiments. (X 6.) 
Upper Helderberg group. Near Buffalo, N. Y. 
