PLATE X 



PAGE. 

 Figs 1 to 4. PACHYDICTTA PUMILA Ulr 157 



I. A group of specimens of the natural size. 



2 and 3. Two fragments, natural size and xg, with some of the zocecial apertures closed. 

 4. The basal part of a rather young example, natural size and xg. (See also plate VIII). 

 Upper part of the Galena shales, near Cannon Falls, Minn. 



Figs. 5 to 10. PACHYDICTTA FOLIATA Ulr 149 



5 to 8. Four specimens of the natural size. Fig. 6 presents the unusual condition of raised 

 maculae. 



9. Surface of fully matured example, xg. 



10. Surface of a young zoarium, xis. (See also plate IX). 



Figs. 11 to 14. PACHYDICTYA TRISERIALIS Ulr . . . . 159 



II. Portion of a block of limestone with a group of the slender ramulets of this species, 



natural size. 



12. Surface of an old example, x18, on which many of the zoosclal apertures preserve the 

 closures. 



13 and 14. Two transverse sections. X25, the first prepared from a young example, the sec- 

 ond from one like the original of fig. 12. 

 Trenton limestone, Montreal, Can. 



Figs. 15 to 20. TRIGONODICTYA CONCILIATRIX Ulr 160 



15 to 1 9. Five specimens of the natural size, illustrating the zoarial variability of the species. 



20. Surface of well preserved example x9. (See also plate IX.) 

 Upper third of the Trenton shales near Cannon Falls, Minn. 



Figs. 21 to 25. STICTOPORELLA CKIBROSA Ulr 184 



21. Nearly complete zoarium of the prevailing type of this species, natural size. 



22. A thin fragment less regularly developed than usual. 



23. Surface of an excellently preserved example, xg. 



24. Another portion of same xis. In this specimen the mesopores are very numerous. 



25. Tangential section of an average specimen, xis. In the upper part of the figure the 



section descends to the level of the prostrate portion of the zocecial tubes. (See also 

 plate XI.) 

 Middle third of the Trenton shales at Minneapolis. 



