PLATE XIII—Continued. 
Stictopora papillosa. 
Page 37. 
See Plate 23 a. 
Fig-. 12. A figure showing the mode of branching and arrangement of cell apertures. 
Lower Helderberg group. Clarksville, N. Y. 
Fig. 13. An enlargement of a fragment showing the form and arrangement of the cell apertures. (X 6.) 
Lower Helderberg group. Clarksville, JV. Y. 
Ptilodictya tenuis. 
Page 39. 
See Plates 17, 23 a. 
Fig. 14. An enlargement of the surface to show the mode of formation of the intercellular longitudinal 
partitions. 
Lower Helderberg group. Clarksville, N. Y. 
FaVOSITES HELDERBERGICE, ETC. 
Fig. 15. A fragment of Favosites Helderbergice which has been overgrown by several other forms of corals 
as represented in the figure, each of which is indicated by a letter, as follows: a. Favosites 
Helderbergice; b. Favosites splicericus; c. Alveolites explanatus; d. Fistulipora ponderosa; 
h. an inclosed cyathophylloid coral. The different expressions of Alveolites, c, are owing to the 
direction in which the cells are cut in a plane section of the mass. 
Lower Helderberg group. Schoharie, N. Y. 
Alveolites explanatus. 
Page 11. 
Fig. 16. An enlargement of the surface, showing the form and striation of the cell apertures of the same 
species as shown in fig. 15. 
Ltciienalia serialis. 
Page 32. 
See Plate 15. 
Fig. 17. An enlargement of the surface to show the form and arrangement of the cell apertures 
Lower Helderberg group. Clarksville, N. Y. 
Fig. 18. An enlargement from the upper side of the epitheca, showing the procumbent position of the 
cellules, and the strong lateral cell walls on the left-hand side of the figure, where the cellules 
have been broken away. 
Lower Helderberg- group. Clarksville, iV. Y. 
Fenestella Noe. 
Page 47. 
Fig. 19. A fragment of a frond, natural size. 
Lower Helderberg group. Clarksville, N. Y. 
Fig. 20. An enlargement of the non-celluliferous side. (X 6.) 
Fig. 21. An enlargement of the celluliferous side of a specimen. 
Lower Helderberg group. Clarksville, N. Y. 
Fig. 22. An enlargement of the celluliferous side. (X 6.) 
Lower Helderberg group. Clarksville, N. Y. 
