PLATE XI. 
Fig. 1. 
Fig. 2. 
Fig. 3. 
Fig. 4. 
Fig. 5. 
Fig. 6. 
Fig. 7. 
Fig. 8. 
Fig. 9. 
Fig. 10. 
Fig. 11. 
Fig. 12. 
Fig. 13. 
Fig. 14. 
Trematopora (Orthopora) regularis. 
Page 16. 
See Plates 13 and 23. 
A piece of limestone with a group of fragments of this species, natural size. 
' Lower Helderberg group. Clarksville, N. Y. 
A specimen showing a rectangular mode of branching. 
Lower Helderberg group. Clarksville, N. Y. 
A piece of limestone with this and other species on the surface. 
Lower Helderberg group. Clarksville, N. Y. 
An enlargement, showing constricted cell apertures, (X 0.) 
Lower Helderberg group. Clarksville, N. Y. 
An enlargement, showing smooth, intermediate ridges. 
An enlargement, showing the transverse and longitudinal intercellular spaces nearly equal. 
An enlargement, showing the longitudinal spaces thickened and serrated. 
Lower Helderberg group. Clarksville, IV. Y. 
A specimen of this species, showing granulose longitudinal ridges and a minute spine at the base 
of each cell aperture. 
Trematopora (Ortpiopora) ovatipora, Hall. 
Page 17. 
See Plate 23. 
A fragment, natural size. 
Lower Helderberg group. New /Salem, N. Y. 
An enlargement, showing the surface characters. The longitudinal interapertural spaces are granu¬ 
lose, the cell apertures are ovate and margined with granulae, and have a minute spine at their 
lower and broader end. 
Lower Helderberg group. New Salem, N. Y. 
A weathered specimen of this species. 
Lower Helderberg Group. Clarksville, N. Y. 
Trematopora (Orthopora) canaliculata. 
Page 17. 
See Plate 23. 
An enlargement from the minute specimen. 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 group. Helderberg Mountains, N. Y. 
Trematopora (Orthopora) parallela. 
Page 19. 
See Plate 23. 
A small fragment of the fossil, natural size. 
A portion of the same enlarged. 
Lower Helderberg group. Clarksville, N. Y. 
