PLATE XVIII. 

 Fene8teli,a (Polypora) oohpaota. 



Page 63. 

 See Plate 22. 

 Fig. 1. A fragment from near the base of a frond, natural size. 

 Fig. 2. An enlargement of the surface of the non-cellulifei-oua side. 

 Fig. 3. An enlargement of a portion of the celluliferous face of the frond. 



Fenesthu-la (Polypora) Arta. 



I'age 83. 

 Fig. 4. A fragment of a frond, showing a diffei-ence in the size of the branches and of the fenestrules on 



the non-celluliferous side, natural size. . 

 Fig. 6. An enlargement of the non-celluliferous face, with slender branches and large fenestrules. 

 Fig. 6. The non-cellulifHrous face of a fragment, natural size. 

 Fig. 7. An enlargement from the preceding, showing stouter branches and smaller fenestrules than fig. 5. 



Fknestella (Polypora) obliqua. 



Page 66. 

 Rg. 8. A fragment of the celluliferous face, natural size. 

 Fig. 9. An enlargement from the above, showing cell apertures, etc. 

 Lower Helderberg group. Near Catskiil, N. T. 



Frnestella (Polypora) paxillata. 



rage 65. 

 Fig. 10. A fi-agment showing the non-celluliferous face of the frond. 



Pig. 11. An enlargement from the above ; one branch is decorticated showing the interior structure. 

 Fig. 12. An enlargement of the celluliferous side of a specimen. 

 Lower Helderberg group. Clarksville, N. Y. 



Fenestella (Polypora) .sp. irnlet. 



Fig. 13. An enlargement from a fragment worn down from the non-cellulil'ei'ous face and showing two, thi-ee 

 and four ranges of cells. 



Fenestella (Polypora) compressa. 



Page 61. 

 Fig. 14. A fi-agment, natural size, presenting the non-celluliferous face. 



Lower Helderberg group. Clarksville, N. Y. 

 Fig. 15. An enlargement fi-om the pi'eceding. 



Fig. 16. An enlargement of the non-cellulifei-ous .side of a specimen, showing the finely granulose strise. 

 Fig. 17. An enlargement from the celluliferous face of a frond, showing the obliquely upward opening of 

 the pores. The surface is modified from weathering. 

 Lower Helderberg group. Clarksville, N. Y. 

 Fig. 18. An enlargement of the cellulifei-ous face of a fragment, showing tke cell apertures opening rect- 

 angularly to the axis. 



Lower Helderberg group. CatskUl creek, N. Y. 



Fenestella (Polypora) Lil.£A. 



Pago 62. 

 Pig. 19. A fragment of the celluliferous face of a frond, natural size. 

 Fig. 20. An enlargement from the preceding. 



Lower Helderberg group. ClarksvilU, N. Y. 

 fig. 21. A fragment of a frond, natural size, showing the celluliferous face. 

 Pi^. 22. An enlargement of the preceding. 



Lower Helderberg group. Schoharie, N. Y. 



