PLATE XXIX—Continued. 
Intrapora PUTEOLATA. 
Page 97. 
Figs. 18-22. Fragments, natural size, showing the ordinary variations in form of different fronds 
Fig. 23. An enlargement of a portion of the surface of a frond, showing circular cell apertures ; the inter- 
apertural pits ou a portion of the figure are obsolete. (X 13.) 
Fig. 24. An enlargement of a part of a frond, showing the form and mode of bifurcation, the arrange¬ 
ment of the cell apertures, the interapertural pits, and the non-celluliferous space at the mar¬ 
gin having indistinct pits arranged in oblique rows, resembling oblique striations. 
Fig. 25. A transverse section of one-half of a frond, enlarged, showing the mesotheca and the uprig-ht 
portion of the cell tubes. (X 6.) 
Fig. 26. An enlargement, to eighteen diameters, of a portion of the specimen, fig. 24, from near the mar¬ 
gin, showing more distinctly the character of the cell apertures and intermediate pits and the 
non-celluliferous striated margin. 
Upper Helderberg group. Falls of the Ohio river. 
Stictopora rhomboidea. 
Page 95. 
Fig. 27. A fragment, natural size. 
Fig. 28. The surface, enlarged, showing- the form and arrangement of the cell apertures. (X 6 ) 
Upper Helderberg group. Near Le Roy , N. Y. 
COSCINOTRYPA CRIBRIFORMIS, V!U\ CARINATA. 
Page 89. 
See Plate 33. 
Fig. 29. A fragment, natural size. 
Fig. 30. A transverse section, natural size. 
Figs. 31-33. Fragments, natural size, showing the common variations of the different fronds in the size of 
the fenestrules and general appearance of the surface. 
Fig. 34. A portion of the surface of a frond, enlarged, showing alternating and imbricating cell apertures. 
(X 18.) 
Fig. 35. An enlargement, showing one of the fenestrules, and the ordinary form and arrangement of the 
denticulated cell apertures. (X 6.) 
Upper Helderberg group. Falls of the Ohio rwer. 
Stictopora perarcta, Hall. 
Page 9G. 
Fig. 36. A fragment, natural size. 
Fig. 37. The surface enlarged, showing- the form and arrangement of the cell apertures. (X 18.) 
Upper Helderberg group. Onondaga Valley, N. Y. 
