PLATE XLIV 



PAGE 



Figs. 1-5. HEMIPHBAGMA IBRASUM (Ulrich) 218 



1. Surface of a zoarium illustrating the usual aspect. X 10. 



2. Tangential section. X 18. 



3. Vertical section exhibiting incomplete diaphragms in mature zone. 



X9. 



4. 5. Two specimens of the branching zoarium. 



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

 Minnesota. 



Figs. 6, 7. DIANULTTES PETROPOLITANUS Dybowski 217 



6. Vertical section. X 9. 



7. Tangential section X 9 and a portion X 35 showing wall structure 



in detail. 



Ordovician (Mohawkian), Trenton shales, Goodhue County, 

 Minnesota. 



Figs. 8-10. HELOPORA SPINIFORMIS Ulrich 228 



8. A segment natural size and lower portion of same. X 18. 

 9, 10. Vertical and transverse sections of a segment. X 18. 



Ordovician (Mohawkian), Stones River (Lebanon) Is., La- 

 vergne, Tennessee. 



Figs. 11-14. RHINIDICTYA NEGLECTA Ulrich 229 



11. Fragment, natural size, and portion of surface X 18, showing the 



usual aspects of the species. 



12. Tangential section. X 18. 



13, 14. Vertical and transverse section. X 18. 



Ordovician (Mohawkian), Trenton Is., Burgin, Kentucky. 



Figs. 15-17. PRASOPORA INBULARIS Ulrich 215 



15. Tangential section exhibiting the numerous mesopores. X 18. 



16. Small portion of a tangential section through a macula and sur- 



rounding zooecia. X 18. 



17. Vertical section illustrating great abundance of cystiphragms and 



diaphragms. X 18. 



Ordovician (Mohawkian), Trenton shales near Cannon Falls, 

 Minnesota. 



Figures are after Ulrich. 



394 



