PLATE XL 



PAGE 



Figs. 1-3. HELOPORA DIVARICATA Ulrich 227 



1. Segment natural size and X 7. 



2. Portion of the same. X 18. 



3. Transverse section. X 18. 



Ordovician (Mohawkian), Black River (Decorah) shales, 

 Minneapolis, Minnesota. 



Figs. 4-6. CHASMATOPORA RETICULATA (Hall) 226 



4. Frond showing the reverse side. 



5. Portion of the same. X 9. 



6. Small fragment exhibiting the reverse or celluliferous side. X 18. 



Ordovician (Mohawkian), Trenton shales, Minneapolis, 

 Minnesota. 



Figs. 7-10. CHASMATOPORA SUBLAXA (Ulrich) 227 



7. 8. Fragments showing obverse and reverse sides. 



9. Celluliferous side of specimen, Fig. 7. X 9. 



10. Reverse side of small fragment, Fig. 8, illustrating striated char- 



acter. X 9. 



Ordovician (Mohawkian), Black River (Decorah) shales, 

 Minneapolis, Minnesota. 



Figs. 11-14. ESCHAROPORA CONFLUENS Ulrich 223 



11. A specimen preserving the pointed articulating base. 



12. Surface of example illustrating arrangement of apertures. X 9. 



13. Vertical section. X 18. 



14. Tangential section of a well preserved fragment. X 18. 



Ordovician (Mohawkian), Black River (Decorah) shales, 

 Minneapolis, Minnesota. 

 Figures after Ulrich. 



390 



