PLATE IX. 
Figs. 1 to 5. PACHYDICTYA FOLIATA Ulr 
1. Tangential section, x18, 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 levei caused 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 lamine. 
bo 
tubes ina well preserved specimen. 
3. Small portion of same x35, to show the minutely tubular character of the zowcial walls. 
Vertical section, 18. 
5. About two thirds of the width of a transverse section, <18,showing median tubuli very 
distinctly. (See also plate X.) 
Lower third of the Trenton shales, St. Paul and Minneapolis. 
Bigs 6:and 105. sPACHYDICTYAy OCCIDENDATISNU Mn ascent eeoteenctenenne chen ctieeceice nee 
6. Represents a small portion of a tangential section just beneath a bifurcation of the 
zoarium, X18. 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 x18. (See also plate VIII). 
Upper third of the Trenton shales at St. Paul. 
igi. 7: (PACH Y DICT YAVA CUA (EV AVI) cic patssecs tis vets acess ote rare oto eveunrors cevoVarane ioiateteyens axelavers ovations Vaterewsieletelaterstetesiets 
Tangential section of a specimen from Cannon Falls, Minn. (See also plate VIII). 
Higs. 8iand’9! SPACHY DICTA WL EGIANS)) Ws eS] everesoyc le tesiereiisyatelaie oieie ie eis ove reiacale eteletetsleuersiereteltinie siehetelsieterensievere 
8. Tangential section, X18, cut obliquely so as toshow parts of both sides of the zoarium. 
This specimen was very old and thick and 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, X35. (See also plate VIII). 
Base of Galena shales, St. Paul, Minn. 
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Higgs Iivand eZ RIGONODICTY-AxCON CIELATR Ix Wl Peace re etltepeioneileleeeidieisiaieiciecicrselseisiareiieieisstesetictet= 
11. Transverse section, X18. 
12. Tangential section, X18, from a specimen in an unusually good state of preservation. 
(See also plate X), 
Upper third of the Trenton shales near Cannon Falls, Minn. 
HGS sand 4s PACH NDI OMA UME RDA ACUI eis rateyetaraistetelsterste = otalaletelatetelalatepselejeleiedsyslel=iatedelalefalststeiiaratelelsye 
13. Tangential section, x18. At the upper end of the figure the section sinks to the level 
of the median lamine. 
14. Small portion of one of the longitudinal interspaces and adjoining walls of several zoce- 
cia, X35. (See also plate VIII). 
Middle third of the Trenton shales, St. Paul and Minneapolis. 
Tangential section X18, showing structure in the outer half of one of the layers of zoccial 
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154 
160 
152 
