PLATE XXXIX— Continued. 



Fenestella (Polypora) hexagonalis var. foraminui^osa. 



Page 165. 

 Pig. 16. A portion of the non-celluliferous face of a frond, natural size. 

 Fi|f. 17. A portion of the cellulifei-ou.s face of a frond, natural size. 

 Fig. 18. An enlargement of a portion of fig. 16, showing the character and comparative .size of the 



branches and dissepiments; on the right of the figure th^ dissepiments foi-m the bases of 



branches growing at right angles to the others. (X 6.) jj^ j,^,^. 



Fig. 19. An enlargement of a portion of fig. 17, showing the form and comparative size of the branches 



and dissepiments, the form and ai-rangement of the cell apertures, and the prominent nodes 



characteristic of this variety. (X 6.) 

 Fig. 20. An enlargement of another portion of fig. 17, showing the non-celluliferous space, immediately 



below the bifurcations, continued downward between the central ranges of cell apertures in 



the form of a gi-adually narrowing shallow gi-oove. The fenestrules are somewhat wider than 



those of fig. 19. (X 6.) 



Upper Helderberg group. IValpole, Ontario, CaJiada. 



r(J lo fioij' -n'tH 



