PLATE LII—Continued. 
Fenestella (Unitrypa) acclivis. 
Page 138. 
Fig. 16. An enlargement of a portion of the non-cellnliferous side of a frond, showing for the most part a 
ridge of prominent nodes along the middle of the branch ; the dissepiments are also nodose. 
(X 6.) 
Fig. 17. An enlargement of a portion of the non-celluliferous face of a frond, the branches having two 
rows of nodes, and the dissepiments being without nodes. (X 6.) 
Fig. IS. An enlargement of the celluliferous face, the carinae broken away, showing the form 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 figure represents the curved processes connecting the carinae. These are for the most part, 
so prominent as to obliterate the summits of the carinae, and might be very easily mistaken 
for some form of encrusting Bryozoa. (X 6.) 
Fig. 20. An enlargement of the mold in the rock of a portion of the non-celluliferous 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 tilling of the cells and fenestrules; the right, the filling of the 
spaces between the processes connecting the carinae. These fillings, which are a deposit of 
siliceous sediment, have in some cases been mistaken for organic structure. (X 6.) 
Fig. 22. An enlargement of the mold of the side of a branch, when the cell apertures and interstices be¬ 
tween the scalae have been filled with siliceous matter. (X 6.) 
Fig. 23. A tranverse section of the branches and carinae enlarged, showing the depth of the scalae 
connecting the carinae. (X 6.) 
Upper Helderberg group. Walpole, Ontario, Canada. 
