PLATE XI—Continued. 
Callopora (Callotrypa) heteropora. 
Page 25. 
See Plates 13 and 23. 
Fig. 32. An irregularly branching form, natural size. 
Lower Helderberg group. Clarksville, N. Y. 
Fig. 33. A bifurcating branch, natural size. 
Lower Helderberg group. Clarksville, N. Y. 
Fig. 34. An enlargement, showing the surface characters, and the small oval cell apertures with inter- 
apertural pits. 
Callopora (Callotrypa) unispina, Hall. 
Page 26. 
Fig. 35. A branching specimen, natural size. 
Lower Helderberg group. Clarksville, N. Y. 
Fig. 36. An enlargement, showing the surface characters—a minute spine at the base of each oval aperture 
with one or two ranges of interapertural pits. 
Lower Helderberg group. Clarksville, N. Y. 
Fig. 37. An enlargement, showing some of the cells with a minute spine, while it is absent from others. 
Lower Helderberg group. Clarksville, N. Y. 
Callopora (Callotrypa) striata. 
Page 26. 
See Plate 23. 
Fig. 38. A small fragment, natural size. 
Lower Helderberg group. Schoharie, N. Y. 
Fig. 39. An enlargement from the surface of the preceding, showing distant oval cell apertures, the inter¬ 
apertural pits elongate quadrangular, and this part of the surface striated. 
Fig. 40. A piece of limestone with some small fragments distributed over the surface. 
Lower Helderberg group. Schohane, N. Y. 
Fig. 41. An enlargement, showing irregularly arranged oval cell apertures without spines at their base, 
and the intermediate spaces striate, without being distinguished by pits. 
