PLATE IX. 



PAGE 

 Pigs. 1 to 5. PACHYDICTYA FOLIATA Ulr 149 



1. Tangential section, xis, cutting the zoarium a little obliquely. The figure which was 



inadvertently placed upside down on the stone represents a spot of the section where 

 inequality of level cause'd the zoarium to be divided in such a manner that it brings 

 into rapid review the various changes from the base of the zocecial tubes to the surface. 

 The shaded and vertically lineate zone in the lower part of the figure represents the 

 median tubuli and laminje. 



2. Tangential section xis, showing structure in the outer half of one of the layers of zocecial 



tubes in a well preserved specimen. 



3. Small portion of same X35, to show the minutely tubular character of the zocecial walls. 



4. Vertical section, xis. 



5. About two thirds of the width of a transverse section, xi8,showing median tubuli very 



distinctly. (See also plate X.) 

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



Figs. 6 and 10. PACHYDICTYA OCCIDENTALS Ulr 151 



6. Eepresents a small portion of a tangential section just beneath a bifurcation of the 



zoarium, xis. At this point it is common to find, as in the present case, that the 

 longitudinal interspaces are wider and with more lines of median tubuli than usual. 



10. Vertical section xis. (See also plate VIII). 

 Upper third of the Trenton shales at St. Paul. 



Fig. 7. PACHYDICTYA ACUTA (Hall) 155 



Tangential section of a specimen from Cannon Falls, Minn. (See also plate VIII). 



Figs. 8 and 9. PACHYDICTYA ELEGANS, n. sp 154 



8. Tangentialsection.xls, cut obliquely so as to show parts of both sides of the zoarium. 



This specimen was very old and thick%nd in the outer part (upper third of figure) de- 

 veloped two extra lines of median tubuli in each longitudinal interspace. The end 

 spaces are also unusually long. 



9. Small portion of same section, xss. (See also plate VIII). 

 Base of Galena shales, St. Paul, Minn. 



Figs. 11 and 12. TRIGONODICTYA CONCILIATKIX Ulr 160 



11. Transverse section, xis. 



12. Tangential section, xig, from a specimen in an unusually good state of preservation. 



(See also plate X). 

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



Figs. 13 and 14. PACHYDICTYA FIMBBIATA Ulr 152 



13. Tangential section, xis. At the upper end of the figure the section sinks to the level 



of the median laminae. 



14. Small portion of one of the longitudinal interspaces and adjoining walls of several zoo3- 



cia, x.35. (See also plate VIII). 

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



