PLATE XIX. 



Figs. 1 to 9. HOMOTBYPA MINNESOTENSIS Ulr 235 



1 to 3. Vertical, transverse and tangential sections xis, of a specimen having the walls in 

 the peripheral region thicker than usual. Mus. Keg. No. 5970. 



3a. Small portion of a tangential section of an example of the var. montifera, x50. Base 

 of the upper third of the Trenton shales at St. Paul. 



4 and 5. Tangential and vertical sections of an average specimen, xis. 



6. The peripheral part of two zooecial tubes, xi8, more closely tabulated than usual. Mus. 

 Eeg. No. 59706. 



7 and 8. Two examples of the natural size. The end view under the latter shows the ex- 

 ceeding narrowness of the peripheral region. 



9. Surface of the original of flg. 7, xg. 



Lower third of the Trenton shales, Minneapolis. 



Figs 10 to 16. HOMOTBYPA EXILIS Ulr 236 



10 and 11. Two fragments of the natural size. 



12. Vertical section xis. 



13. Tangential section in a pre-mature condition, xis. 



14. Tangential section showing fully matured characters, xis. 



15. Portion of flg. 14 more highly magnified. 



16. Portion of flg. 13 more highly magnified. 

 Lower third of the Trenton shales at Minneapolis. 



Figs. 17 to 20. HOMOTKYPA SEPARATA, n sp 237 



17 and 18. Tangential section of this peculiar species, xis, and a portion of same xso. 



19. Surface of a well marked specimen xg. 



20. Vertical section xia Attention is to be directed to the tabulated interstitial spaces. 

 Lower third of the Trenton shales, Minneapolis. 



Figs. 21 to 28. HOMOTKYPA SUBKAMOSA Ulr 239 



21. View of a characteristic specimen showing the irregular division of the branches. 



22. 24 and 25. A series of three tangential sections xis, agreeing in all respects except that 



while in the first the acanthopores are numerous and well developed they are fewer in 

 the second and quite inconspicuous in the third. Original of flg. 24 belongs to Survey 

 Museum, Reg. No. 5980a. 



23. Small portion of flg. 22 more highly magnified. 



26. Vertical section xis, of a specimen having the outermost region loosely tabulated; very 



unusual. Mus. Reg. No. 59806. 



27. Vertical section of a typical example, xi8. 



28. Surface of an average example, showing the cystiphragms in the zooecial apertures, xg. 

 Upper third of the Trenton shales, St. Paul and near Cannon Falls. 



