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PLATE X. 
Trematopora ? (Trematella ?) CORTICOSA. 
Page 15 
See Plate IB. 
1. A branching'fragment, natural size. 
Lower Helderberg group. Clarksville, JST. Y. 
2. An enlargement from the preceding, showing the regularly oval cell apertures. 
3. An enlargement from another specimen, showing the presence of elevated ridges between the 
ranges of cell apertures. 
Lower Helderberg group. Clarksville, N. Y. 
4. An enlargement showing cell apertures somewhat transversely arranged, and a little more elongated 
than in tigs. 1 and 2. A fragment of a Callotrypa adheres to the upper part of the specimen. 
5. An enlargement showing various forms of cell apertures. 
Lower Helderberg group. Clarksville, N. Y. 
6. An enlargement from a translucent section, showing the cell walls, the septa, and the divergence 
of the cells toward the surface. 
7. A specimen of natural size, showing a rectangular mode of branching. 
Lower Helderberg group. Clarksville, N. Y. 
8. A specimen of natural size, showing the branches diverging almost rectangularly. 
9. A curving stipe with the branches diverging rectangularly from one side. 
Lower Helderberg group. Clarksville, N. Y. 
10. A branching stipe where the long branch on the right-hand side shows the mark of a branch 
broken from the upper side, and the base of one coming off on the lower side. 
Lower Helderberg group. Clarksville, N. Y. 
Ch^etetes (Monotrypella) densus. 
Page 14. 
11. A branching specimen of natural size. 
Lower Helderberg group. Clarksville, N. Y. 
12. An enlargement showing the surface characters, cell apertures, etc. 
Lower Helderberg group. Clarksville, N. Y. 
IB. A longitudinal section enlarged, showing the mode of increase in the cells, their freedom from 
septa in the center of the branch, and their septate characters as they approach the apertures. 
Diamesopora constricta. 
Page 19. 
See Plate 23 a. 
14. A fragment, natural size, showing in part the poriferous surface, and where the branch is broken, 
the wrinkled interior of the epitheca. 
15. An enlargement from the preceding, showing areas of larger cells and their mode of radiating 
from the more prominent ones. 
16. Fragments on a piece of limestone ; the upper part of the right-hand specimen in the figure is of 
this species, growing upon or incrusting another form shown below it. 
Lower Helderberg group. Clarksville, N. Y. 
17. A surface enlargement from the preceding, showing a more regular arrangement of cell apertures 
than in fig. 15. The cell apertures are more trilobate than represented in the figure. 
18. A bifurcating fragment of the species. 
Lower Helderberg group. Clarksville, N. Y. 
19. An enlargement from fig. 18, showing the constriction of the cell apertures. 
Diamesopora dispersa. 
Page 20. 
20. A fragment, natural size. 
21. An enlargement from the surface of the preceding, showing the form and irregular distribution 
of the cell apertures. 
Lower Helderberg group. Clarksville, N. Y. 
