PLATE XXVIII. 
Lichenalia, sp. ? 
Fig. 1. An enlargement of a portion of the weathered face of a specimen, showing the form and arrange¬ 
ment of the recumbent portion of the cell tubes as they lie upon the epitheca. (X 6.) 
,| Upper Helderberg group. 
Acanthoceema divergens. 
Page 73. 
Fig. 2. The natural size of a specimen, showing the form and mode of branching. 
Upper Helderberg group. Onondaga Valley, N. Y. 
Acanthoclema ovatum. 
Page 73. 
Fig. 3. An enlargement of a portion of a specimen, showing the form and arrangement of cell aper¬ 
tures, with ridges separating the longitudinal ranges of apertures. (X 6.) 
Upper Helderberg group. Onondaga Valley, N. Y. 
Stictopora linearis. 
Page 96. 
See Plate 27. 
Fig. 4. An enlargement of a portion of a specimen, showing the form and arrangement of cell aper¬ 
tures, and the longitudinal ridges separating the ranges of apertures. (X 0.) 
Fig. 5. An enlargement of a portion of a weathered specimen. The surface between the cell walls is 
worn away, giving to the surface the appearance of having contiguous, quadrangular cell 
apertures. 
Upper Helderberg group. New York. 
Acanthoclema triseriale. 
Page 74. 
Fig. 6. A specimen, natural size. 
Fig. 7. A portion of the preceding enlarged, showing the form and arrangement of the cell apertures, 
and the strong granulose ridges separating the longitudinal ranges. (X 6.) 
Upper Helderberg group. Near Caledonia, N. Y. 
Prismopora triquetra. 
Page 97. 
See Plate 29. 
Fig. 8. A specimen, natural size. 
Fig. 9. An enlargement of a portion of a specimen, giving an oblique view of two of the three faces. 
(X 6.) 
Fig. 10. An enlargement from the same specimen, showing- the concave face, and the form and arrange¬ 
ment of the cell apertures. 
Upper Helderberg group. Falls of the Ohio river. 
Prismopora paucirama. 
Page 98. 
See Plate 29. 
Fig. 11. An enlargement of a transverse section, showing the internal plates radiating from the center to 
each of the angles, a few of the cell tubes, and the intercellular vesiculose structure. (X 6.) 
Upper Helderberg group. Thompson’s lake, Albany Co., N. Y. 
