PLATE XXXII — Continued. 
Lichenalia geometrica. 
Page 79. 
Fig. 21. A fragment, natural size. 
Fig. 22. An enlargement of one of the maculae, showing the smooth or carinated radiating cell tubes, with 
oval apertures, and the character of the intermediate space. (X 18.) 
Fig. 23. A portion of the surface of the specimen fig. 21, incrusting a Fenestella. (X 6.) 
Upper Helderberg group. Falls of the Ohio river. 
Prismopora sparsipora. 
(See Supplement.) 
Fig. 24. A fragment, natural size. 
Fig. 2f>. An enlargement of the surface from the preceding, showing the arrangement of the cell apertures, 
and the non-celluliferous margin of the frond. (X 6.) 
Fig. 26. A portion of the surface still further enlarged. The figure, erroneously, shows two minute 
opposite denticulations in each cell aperture. (X 6.) 
Fig. 27. A transverse section of a specimen, apparently of the same species, which shows a tubular mode 
of growth. 
Upper Helderberg group. 
Lichenalia sp. inclet. 
Fig. 28. A portion of the surface of a species of this genus, showing the contraction, and final closing of the 
cell apertures by a thickening of the superficial tissue. 
Upper Helderberg group. 
I 
