PLATE XI—Continued. 
Trematopora (Orthopora) rhombifera, Hall . 
Page 18. 
See Plate 23. 
Fig-. 15. (15a.) Two specimens of natural size, showing- the extremes of size. 
Lower Helderherg- group. Clarksville, N. Y. 
Fig. 17. A specimen, natural size, having the principal branches nearly parallel with the main one, which 
is bifurcated above. 
Lower Helderberg group. Clarksville, N. Y. 
Fig. 18. A larger branching specimen, natural size. 
Lower Helderberg group. Clarksville, N. Y. 
Fig. 19. An enlargement showing the arrangement and form of apertures, with the interapertural partitions. 
Lower Helderberg group. Clarksville, N. Y. 
Fig. 20. An enlargement of a bifurcating branch where the cell apertures are constricted by the thickening 
of the intercellular substance. 
Lower Helderberg group. Clai'ksville, N. Y. 
Stictopora granatula. 
Page 38. 
See Plate 23 a. 
Fig. 16. A specimen, natural size. 
Lower Helderberg group. Catskill Creek, N. Y. 
Lichenalia crassa. 
Page 30. 
Fig. 21. A flattened or crushed branching form, showing a distinct poriferous surface. 
Fig. 22. An enlargement from fig. 21, showing the round and regularly arranged cell apertures in some 
parts, while the maculae are without cell apertures. 
Lower Helderberg group. Schoharie, N. Y. 
Callopora (Callotrypa) macropora. 
Page 24. 
See Plate 23. 
Fig. 23. A weathered branching specimen, natural size. 
Lower Helderberg group. Catskill Creek, N. Y. 
Fig. 24. An enlargement from fig. 23. 
Fig. 25. A bifurcating branch, natural size. 
Lower Helderberg group. Clarksville, N. Y. 
Fig. 26. An enlargement from the preceding, showing oval cell apertures and mostly one range of inter¬ 
apertural pits. 
Fig. 27. A slender, branching form of this species. 
Tentaculite limestone. Schoharie, N. Y. 
Fig. 28. A small branching fragment. 
Lower Helderberg group. Schoharie, JS T . Y. 
Fig. 29. An enlargement from fig. 28, with larger cells than in fig. 26, and with few and irregularly dis¬ 
posed interapertural pits. 
Callopora (Callotrypa) macropora var. signata. 
Page 25. 
Fig. 30. A branching specimen, natural size. 
Fig. 31. An enlargement from the preceding, showing cell apertures with occasional interapertural pits. 
Lower Helderberg group. Clarksville, N. Y. 
