PLATE IX. 



GONIOTRYPA BILATERALTS, (page 41). 



Figure I- Small segment of the natural size, and portion of same, x 18. 



Pachydictya hexagonalis, (page 42). 



Figure 2. A fragment of the bifoliate zoarium of this species, of the natural 

 size, showing the arrangement of the apertures of the zooecia 

 and clusters of large cells. 



Figure 2a. Portion of same, x 9. 



Figure 26. Small portion of a vertical section, x 18, showing the tabulation of 

 the zooecial tubes, the interstitial vesicles, and the solid filling 

 of the latter just below the surface. 



Figure 2c. Small portion of a tangential section, x 18. The upper end of the 

 figure represents the appearance of the section when it passes 

 through the zoarium at a depth from the surface equal to one- 

 half of the thickness of one of its leaves- The lower end shows 

 the character of the interspaces just beneath the surface. 



Batostoma Manitobense, (page 39). 



Figure 3. Portion of the surface of a specimen with numerous mesopores, x 9. 

 Figure 3a. Vertical section, x 18, showing the tabulation of the zooecia and 



mesopores, and the thickened condition of their walls just 



beneath the surface. 



Figure 36. Tangential section, x 18, showing the ring-like walls of the zooecia, 

 the number and distribution of the mesopores, and the incon- 

 spicuous character of the acanthopores of an average specimen. 



Figure 3c. Small portion of a tangential section, x 18, prepared from a speci- 

 men like that from which fig. 3 was draw^n. In it, the 

 zooecia are more circular and their walls thinner than usual. 



Leperditia subctlindrica, (page 49). 



Figure 4. View of the left side of a complete carapace, x 18, showing the 



overlapping edge of the right valve. 

 Figure 4a. End view of the same, x 18. 

 Figure 46, Ventral profile view of the same in outline, x 18. The irregular 



line is intended to represent the overlapping edge of the right 



valve. 



Figure 5. 



Aparchites minutissimus, (page 49). 



A right valve of this species, x 18, with the central region unusually 

 prominent. Many specimens are simply strongly convex. 



