PLATE X. 



TrEMATOPORA ? (TkEMATELLA?) C0RTIC08A. 

 Page IS 

 See Plate 13. 

 Fig. 1. A. branching' fi-apnent, natural size. 



Lower Helderberg group. Clarksville, N. Y. 

 Fig. 2. An enlargement from the pi-eceding. showing the regularly oval cell apertures. 

 Fig. 3. An enlargement fi-ora another specimen, showing the presence of elevated ridges between the 

 ranges of cell apertures. 



Lower Helderberg group. Clarksville, iV. Y. 

 Fig. 4. An enlargement showing cell apertuiv.s somewhat transveraely arranged, and a little more elongated 

 than in figs. 1 and 2. A fragment of a Callotrypa adheres to the upper part of the specimen. 

 Fig. 5. An enlargfement showing vai-ious form.s of cell apertui-ea. 

 Lower Helderberg group. Clarksville, N. Y. 

 Fig. 6. An enlargement from a translucent section, showing the cell walls, the septa, and the divergence 



of the cells towai-d the surface. 

 Fig. 7. A specimen of natural size, showing a rectangular mode of branching. 



Lower Helderberg group. Clarksville, N. Y. 

 Fig 8. A specimen of natural size, showing the branches diverging almost rectangularly. 

 Fig. 9. A curving stijie with the branches diverging rectangularly from one side. 



Lower Helderberg group. Clarksville, N. Y. 

 Fig. 10. A branching stipe where the long branch on the light-hand side shows the mark of a branch 

 broken from the upper side, and the ba-se of one coming off on the lower side. 

 Lower Helderberg group. Clarksville, N. Y. 



CHiETETES (MoNOTRYPELLA) DENSUS. 



Page 14. 

 Fig. 11. A branching specimen of natural size. 



Lower Helderberg group. Clarksville, N. Y. 

 Fig. 12. An enlargement showing the sui-face characters, cell apertures, etc. 



Lower Helderberg group. Clarksville, N. Y. 

 Fig. 13. 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 charactera as they appix>ach the apertures. 



Diamesopora constriota. 



Page 19. 

 See Plate 23 A. 



Fig. 14. A fragment, natural size, showing in part the poriferous surface, and where the branch is broken, 



the wrinkled interior of the epitheca. 

 Fig. 15. An enlargement from the preceding,- showing areas of larger cells and their mode of radiating 



from the more prominent ones. 

 Vig. 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. 

 Fig. 17. A surface enlargement fi-om the preceding, showing a more regnilar arrangement of cell apertures 



than in fig. 15. The cell apertures are more trilobate than repi-esented in the figure. 

 Fig. 18. A bifurcating fragment of the species. 



Lower Helderberg group. Clarksville, N. Y. 

 Rg. 19. An enlargement from fig. 18, showing the constriction of the cell apertures. 



Diamesopora disperaa. 



Pago 20. 

 Fig. 20. A fragment, natural size. 



Pig. 21. An enlargement from the surface of the preceding, showing the form and irreg^ular distribution 

 of the cell apertures. 



Lower Helderberg group. Clarksville, N. Y. 



