.-Inill-yi /-I'tv 'J. 



PLATE LII— Continaed. 



Fenestella (Unitrtpa) acclivis. 



Page 138. 



Vig. 16. An enlargement of a portion of the non-celluliferous side of a frond, showing- for the most part a 

 ridg« of prominent nodes along the middle of the branch ; the dissepiments ai-e also nodose. 

 (X 6.) 



Fig. 17. An enlargement of a portion of the non-celluliferous face of a frond, the bi'anches having two 

 i*ows of nodes, and the dissepiments being without nodes. (X 6.) 



Fig. 18. An enlargement of the celluliferous face, the cariiiaB broken away, showing the foiin and arrange- 

 ment of the cell apertures. (X 6.) 



Fig. 19. An enlargement ; the lower left hand corner represents a bifurcating branch ; the remainder of 

 the figui-e represents the curveii pi-ocesses connecting the carinse. These are for the most part 

 BO prominent as to obliterate the summits of the cai'inse, and might be very easily mistaken 

 for some form of encrusting Bryozoa. (X 6.) 



Fig. 20. An enlai-geraent of the mold in the rock of a portion of the non-celluIifei"OUS face of a frond. (X 6-) 



Fig. 21. An enlargement of the mold left in the rock by the dissolving away of a frond ; the left portion 

 of the figure represents the filling of the cells and fenestrules ; the light, the tilling of the 

 spaces between the processes connecting the carina. These fillings, which are a deposit of 

 siliceous sediment, have in some cases been mistaken for orgaiiic structure. (X ti.) 



Fig. 22. An enlargement of the mold of the side of a branch, when the cell apertures and intei-stices be- 

 tween the scalte have been filled with siliceous matter. (X 6.) 



Fig. 23. A tranvei'se section of the branches and cai'inK enlai-ged, showing the depth of the scales 

 connecting the carinae, (X t5.) 



Upper Heldei'berg group. Walpole, Ontario, Cavada. 



