PLATE XII. 



TJENIOPORA. 



(Page 533.) 

 T^J^IOPOKA. EXCGUA, Hall. 



Figs. 1, 2. Portions of fronds, natural size. 



Fig. 3. A transverse section of the triangular main branch of fig. 



1, x6. Compare this figure with fig. 15, Prismopora 



triqiietra. 

 Fig. 4. An enlargement of a portion of a frond. x6. 

 Fig. 5. An enlargement from a specimen having only two ranges 



of cell apertures on each side of the carinas. x6. 

 Hamilton group. N'ew York. 



STICTOPORINA. 



(Page 532.) 



StICTOPOEINA SUfiCARINATA. 



Fig. 6. This figure is inserted here for comparison with figs. 1 and 2. 

 Hamilton group, N'ew York. 



THAMNOTRYPA. 



(Page 546.) 

 Thamnoteypa divaeicata, Hall. 

 Fig. 7. A frond, natural size. 

 Fig. 8. A portion of the same. 6x. 



Upper Helderberg group. Near Buffalo^ JV. Y. 



PRISMOPORA. 



(Page 531.) 

 Peismopoea tbiquetea, Hall. 



Figs. 9, 10. Two specimens, natural size. 



Fig. 11. A portion of one face of a branch. x6. 



Fig. 12. An enlargement, showing the denticulated cell apertures. 

 xl8. 



Fig. 13. A transverse section, showing the mesotheca and inter- 

 cellular vesiculose tissue. x6. 



Fig. 14. A natural transverse section showing mesotheca and cell 

 tubes. x6. 

 Upper Helderberg group. Mills of the Ohio. 



642 



