PLATE XIII. 



Trematopoka (Orthopora) regularis. 



Page 18. 

 See Plates 11, 23. 

 Fig-. 1. An enlargement of a small branch where the cells are not separated by a longitudinal ridg-e, and 

 the interspaces are marked by comparatively strong- apinides. (X 6.) 

 Lower Helderberg- group. Clarksville, N. Y. 

 Fig. 2. A fragment enlarged, having ajiertui-es elongated from weathering. The spinules in the inter- 

 spaces ai-e fewer and more slendei- than in the preceding specimen. (X 6.) 

 Lower Helderberg group. Clarksinlle. N. Y. 

 Fig. 3. A fi-a^ient of another indivi<lual enlarged as the preceding. The surface presents an unusual num- 

 ber of ranges of cells, and the interai)ertural ci-enulate ridges are remarkably well preserved. 

 Lower Helderberg group. Clarksville, iV. Y. 



Trkmatopora ? (Trematella ?) CORTICO.'SA. 



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, iV. If. 



CaLLOPORA (CaLLOTRYPa) HETEltOPORA. 

 Page 2». 

 See Plates 11, 23. 

 Fig. 5. A bi-ancbing fragment showing the natm-al size and mode of branching. 



Lower Helderberg group. Clarksville, iV. Y. 

 Fig. 6. A fragment of limestone preserving specimens of this species, with Treinatapora (Orthopara) 

 regularis and a 8j>ecies of Fenestella. 



Lower Helderberg gi-oup. Clarksville, N. Y. 

 Fig. 7. An enlargement from fig. 5, showing the disposition of the cell apertui-es and the minute spines at 



their margins. 

 Fig, 8. An enlargement of a fragment of * branch of this species, where the spinules are so closely dis- 

 posed as to obscure the cell apertures. 



Lower Helderberg group. Albany county, N. Y. 



CaLLOPOKA CELLUI.OSA. 



Page 21. 



See Plates 12, 23 a. 



Pig. 9. A fragment of a branch enlarged, showing the closely arranged spinules on the margins of the 



cell ajiertures, and the interai)ertural pitted surface. (X 6.) 



Lower Helderberg group. Clarksville, N. Y. 



Callopora (Callotrypa) OCULIFERA. . ^ 



, / Page 27. 

 , See Plate 23. 

 Pig. 10. A fragment of a branch enlarged, showing the form and aiTangement of the cell apertures and the 

 interapertural pitted surface. (X 6.) 



Lower Helderberg gi-oup. Near Catskill. N. Y. 

 Fig. 11. A fragment of limestone, showing the mode of occurrence of these forms of Oallopoka, Fknes- 



TMLLA, etc. 



Lower Helderberg group. Clarksville, N. Y. 



