PLATE XI. 



Trematopoua (Okthoi'oha) uegularis. 



Page 16. 

 See Plates 13 and 23. 

 Fig. 1. A piece of limestone with a group of fragments of this species, natural size. 



Lower Helderberg group. Clarksville, N. Y. 

 Fig. 2. A specimen showing a rectangular nioile of branching. 



Lower Helder1)erg group. Clarksville, N. Y. 

 Fig. 3. A piece of limestone with this and other species on the surface. 



Lower Helderberg group. Clarksville, N. Y. 

 Fig. 4. An enlargement, showing constricted cell apertures. (X 6.) 



Lower Helderberg group. Clarksville, iV. Y. 

 Fig. 5. An enlargement, showing smooth, intermediate ridges. 



Fig. 6. An enlargement, showing the transverse and longitudinal intercellular spaces neai-ly equal. 

 Fig. 7. An enlargement, showing the longitudinal spaces thickened and serrated. 



Lower Helderberg group. Clarksville, N. Y. 

 Fig. 8. A specimen of this species, showing gi-anulose longitudinal ridges and a minute spine at the base 

 of each cell aiierture. 



Tbematopora (Orthofora) ovatipora, Hall. 



Page 17. 



See Plate 28. 

 Fig. 9. A fragment, natural size. 



Lower Helderberg group. New Salem, N. Y. 

 Fig. 10. An enlargement, showing the surface charactei-s. The longitudinal interapertural spaces are granu- 

 lose, the cell apertui-es are ovate and margined with granule, and have a minute spine at their 

 lower and broader end. 



Lower Helderberg group. Nete Salem, 2V. Y. 

 Fig. 11. A weathered specimen of this si>ecie8. 



Lower Helderberg Group. Clarksville, N. Y. 



Trematopora (Orthopora) canaliculata. 



Page 17. 

 See Plate 23. 

 Fig. 12. An enlargement from the minute S])ecimen. The margins of the cells are raised and the inter- 

 apertural spaces channeled and with comparatively strong granules at the extremities of the 

 cells and on other parts of the surface. 



Lower Helderberg gi-oup. Helderberg Mountains, N. Y. 



Trematopora (Orthopora) parallela. 



Page 19. 

 See Plate 23. 

  Fig. 13. A small fragment of the fossil, natural size. 

 Fig. 14. A portion of the same enlarged. 



Lower Helderberg group. Clarksville, N. Y. 



