PLATE XXII. 
Fenestella (Unitrypa) Nervia. 
Page 55. 
Fig'. 1. The celluliferous face of a funnel-shaped frond. 
Lower Helderberg group. Clarksville, N. F. 
Fig. 2. An enlargement of the preceding, showing the cell apertures, with a portion of the surface ex¬ 
foliated, disclosing the interior structure, cell walls, etc. 
Fig. 3. An enlargement from the celluliferous face of specimen fig. 1, where the carinal crests are ex¬ 
tended into lateral bars, meeting those from the opposite side. 
Fig. 6. An enlargement from the celluliferous face of another specimen. 
Fig, 9. A fragment; natural size, showing the extension of the lateral bars connecting the intercellular 
carinse. 
Lower Helderberg group. Clarksville, N. Y. < 
Fig. 10. An enlargement of the preceding. 
Fenestella (Polypora) comp acta. 
Page 63. 
See Plate 18. 
Fig. 4. The non-celluliferous face of a fragment. 
Fig. 5. An enlargement from the preceding. 
Lower Helderberg group. Clarksville, N. Y. 
Fenestella adornata. 
Page 66. 
Fig. 7. An enlargement of the non-celluliferous face. 
Lower Helderberg group. Clarksville, N. Y. 
Fig. 8. An enlargement of the celluliferous face of the preceding. 
Fenestella (Unitrypa) Nervia, var. constricta. 
Page 56. 
Fig. 11. An enlargement of the non-celluliferous face, showing the thickened granulated branches and small 
fenestrules. 
Fig. 12. An enlargement from the celluliferous face of the preceding specimen, showing the thickened 
intpr-cellular crests and connecting bars on a part of the surface. 
Fenestella (Hemitrypa) biserialis. 
Page 57. 
Fig. 13. The base of the celluliferous side of a funnel-shaped frond, natural size. 
Fig. 16. An enlargement of the non-celluliferous face of another specimen. 
Fig. 17. An enlargement of the celluliferous face from the specimen tig. 13, where the elevated crests of 
the intercellular carinae are broken off showing the cell-apertures. 
Fig. 18. An enlargement from the celluliferous side of specimen tig. 13, preserving the elevated crests of 
the carinre, and the lateral processes uniting in a longitudinal bar. 
Lower Helderberg group. 1Year Clarksville, JSf. Y. 
Fenestella (Hemitrypa) biseralis, var. exilis. 
Page 57. 
Fig. 14. A sectional view enlarged, showing the elevation of the intercellular crests and the connecting 
processes. (X 4.) 
Fig. 15. An enlargement from the non-celluliferous face of a specimen. 
Lower Helderberg group. Near Clarksville, N. Y. 
