PLATE XIII. 
Trematopora (Orthopora) regularis. 
Page 16. 
See Plates 11, 23. 
Fig-. 1. An enlargement of a small branch where the cells are not separated by a longitudinal ridge, and 
the interspaces are marked by comparatively strong spinules. (X 6.) 
Lower Helderberg group. Clarksville, N. Y. 
Fig. 2. A fragment enlarged, having apertures elongated from weathering-. The spinules in the inter¬ 
spaces are fev r er and more slender than in the preceding specimen. (X 6.) 
Lower Helderberg group. Clarksville, N. Y. 
Fig-. 3. A fragment of another individual enlarged as the preceding. The surface presents an unusual num¬ 
ber of ranges of cells, and the interapertural crenulate ridges are remarkably well preserved. 
Lower Helderberg- group. Clarksville, N. Y. 
Trematopora ? (Trematella ?) corticosa. 
Page 15. 
See Plate 10. 
Fig. 4. A natural longitudinal section showing the mode of growth and the angular forms of the cell tubes. 
Lower.Helderberg group. Clarksville, N. Y. 
Callopora (Callotrypa) heteropora. 
Page 25. 
See Plates 11, 23. 
Fig. 5. A branching fragment showing the natural size and mode of branching. 
Lower Helderberg group. Clarksville, JY. Y. 
Fig. 6. A fragment of limestone preserving specimens of this species, with Trematapora (Orthopora) 
regularis and a species of Fenestella. 
Lower Helderberg- group. Clarksville, JY. Y. 
Fig. 7. An enlargement from tig. 5, showing the disposition of the cell apertures and the minute spines at 
their margins. 
Fig. 8. An enlargement of a fragment of a branch of this species, where the spinules are so closely dis¬ 
posed as to obscure the cell apertures. 
Lower Helderberg group. Albany county, JY. Y. 
Callopora cellulosa. 
Page 21. 
See Plates 12, 23 a. 
Fig. 9. A fragment of a branch enlarged, showing the closely arranged spinules on the margins of the 
cell apertures, and the interapertural pitted surface. (X (5.) 
Lower Helderberg group. Clarksville, JY. Y. 
Callopora (Callotrypa) oculifera. 
Page 27. 
See Plate 23. 
Fig-. 10. A fragment of a branch enlarged, showing the form and arrangement of the cell apertures and the 
interapertural pitted surface. (X 0.) 
Lower Helderberg group. Near Catskill, N. Y. 
Fig. 11. A fragment of limestone, showing- the mode of occurrence of these forms of Callopora, Fenes¬ 
tella, etc. 
Lower Helderberg group. Clarksville, N. Y. 
