PLATE XXIV. 



"ti A /3fl* 



Fig. 1 to 4. HEMIPHRAGMA OTTAWENSE (Foord) 300 



1 and 2. Two portions of a tangential section xis, showing differences due to age. 



3. Vertical section xg. 



4. Small portion of the peripheral region of the same X35. 



Upper part of the Galena shales, Mantorville, Minn. Survey Museum, Reg. No. 6002. 



Figs. 5 to 19. HEMIPHRAGMA IRRASUM Ulr 299 



5. Vertical section xg. 



6. 7, 9 and 14. Four tangential sections xis, exhibiting individual variations. 

 8. Small part of a transverse section xis. 



10 to 13. The surfaces of four specimens xg, fig. 10 representing a Kood average, flg. 12 the 

 appearance of young examples, and figs. 11 and 13 the fully matured conditions. 



15 to 19. A group of five specimens, three of them of the average size, while 17 is the largest 



and 18 one of the smallest seen. 



Lower third of. the Trenton shales afr Minneapolis, and the Galena shales near Cannon 

 Falls, Minn. 



Figs. 20 to 23. HEMIPHRAGMA TENUIMTJRALE, n. sp , 301 



20. Vertical section xis. 



21 and 22. Tangential sections x]8, the first showing the fully matured condition, the 

 second a younger stage in the development of the zoarium. 



23. Surface of a well preserved example showing the incomplete diaphragms in the zooecial 



cavities, xg. 

 Galena shales near Cannon Falls. 



Figs. 24 to 31. STROMATOTRYPA OVATA, n. sp 302 



24. Surface of an old example xg. 



25. Well preserved specimen consisting of several layers, natural size. 



26. Small portion of one of the first layers of same xis, showing an aged condition. 



27. Part of the last layer of same xis, showing appearance of surface in the youngest stage 



observed. 

 28 and 29. Tangential and vertical sections xis, of an example consisting of three distinct 



layers of zooecia 

 30 and 31. Another pair of sections, vertical and tangential, the latter illustrating a more 



aged condition than is shown in flg. 28; xis. 

 Middle third of the Trenton shales, St. Paul and Minneapolis. 



