PLATE XXXVIII. 



Fenestella (Polypora) porosa. 



Page 163. 

 Vig. 1. The non-celluliferoiis side of a specimen, natural size, showinff considerable variation in the size 



of the branches on different portions of the frond. 

 Pig. 3. Another specimen, natural size, the branches being nearly uniform and smaller than those of fig. 1. 

 Fig. 3. The celluliferous side of a specimen, natural size. 

 Fig. 4. An piilargement of a portion of fig. 1, showing more distinctly the variation in the size of the 



branche.s, and the character of the branches and dissepiments. (X 6.) 

 Fig. 5. An enlargement of a jwrtion 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 . 



(X6.) 

 Kig. tj. An enlargement of a poHion 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. 



(X6.) 



Upper Helderberg group. Walpole, Ontario, Canada. 



Fenestella (Polypora) perundata. 



Page 1«3. 



Fig. 7. A iKirtion of the non-celluliferous face of a frond, natural size ; the branches over a portion of the 

 fi-ond ai-e quite regularly arranged and united by anastomosis. 



Fig. 8. A iMirtion of the non-celluliferous face of another frond, in which the branches are more irregular 

 than those of fig. 7. 



Fig. 9. A i)ortion of the .celluliferous face of a frond, showing the size of the branches and their manner 

 of growth. 



Fig. 10. An enlargement of a portion of fig. 7, showing more distinctly the character of the branches and 

 their connection by anastomosis. (X 6.) 



Fig. 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.) 



Fig. 12. An enlargement of a portion of fig. 9, showing the regularly sinuous form of the branches, and 

 the foi-m and aiTangement of the cell apertures. (X 6.) 



Pig. 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 fonn of a narrow groove. 

 Upper Helderberg group. Walpole, Ontario, Canada. 



Fenestella (Polypora) hexagonalis. 



Page 16 1. 



Pig. 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. 



Pig. 1.'). A portion of the celluliferous face of a frond, natural size, showing the regularly sinuous form of 

 the branches. 



Pig. 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 roundeci form. 



Fig. 17. An enlargement of a portion of fig. 14, showing more distinctly the charactei'of the branches and 

 dissepiments and their comparative size. (X ti.) 



Fig. 18. An enlargement of a portion of the non-celluliferous face of a frond. The bi-anches and dissepi- 

 ments are pai-tially imbedded in the rock, which gives to them the appearance of being nar- 

 rower than they really are. (X 6.) 



Rg. 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 *>.) 



Fig. 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 fonn of a narrow groove. Compared with fig. 19, the branches 

 of this si>eciinen are wider, not angular ; the fenestrules are longer and narrower. 

 Upper Helderberg group. IValpole, Ontario, Canada. 



