PLATE XVII. 



tfigs. 1 to 8. MESOTRYPA INFIDA Ulr 258 



Iand2. Two tangential sections prepared from the same example, xi8. The first illus- 

 trates the fully matured condition, the second an earlier level in the zoarium. Tren- 

 ton shales near Fountain, Minn. 



3 to 5. Three portions of a large vertical section of the same, xis, showing the variable 

 disposition and appearance of zocecial diaphragms. 



6. Portion of another vertical section of same x 18. Mus. Reg. No. 5993. 



7. Surface of same, xg, showing a condition approximately intermediate between figs. 1 



and 2. 



8. Surface of a parasitic specimen in a condition corresponding with fig. 1. Middle third 



of the Trenton shales, Minneapolis. 



Figs. 9 to 12. MESOTRYPA (?) SPINOSA, n. sp 259 



9. Surface of well preserved example, showing the round form and regular arrangement of 



the zooecial apertures, and the strong acanthopores; xg. 

 10 and 11. Tangential section, *18, and parts of several zocecia XSQ. 



12. Small portion of a vertical section, xis, showing unmistakable cystiphragms in the 



lower half. Other parts of the same section are like flgs. 3 and 4 of this plate. 

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



Figs. 13 to 21. ASPIDOPORA ELEGANTULA, n. sp 256 



13. A fine example of this species on the surface of which an intermittent second layer of 



zooecia was forming; natural size. 



14. One of the areas of the secondary layer, xg. 



15. Tangential section prepared from the primary layer of same, *18. 



16 and 17. Views of the upper and lower sides of a specimen that consists of at least four 

 distinct layers grown loosely over each other; natural size. 



18. Upper surface of same, xg. 



19. Tangential section of one of the layers of same, x]8. 



20. Parts of several zocecia of a tangential section, X50. 



21. Several zocecia and mesopores as seen in a vertical section of one of the layers, xig. 

 Galena shales, Kenyon, Minn. These two specimens were collected by W. H. Scofleld 



and kindly presented by him to the author. 



Figs. 22 to 25. PRASOPORA LENTICULARIS, n. sp 253 



22. Upper surface and sectional view of an example of this species; natural size. 



23. Two portions of a tangential section of same, xis. the upper half representing the ap- 



pearance in the upper third, the lower half that in the basal third of the zoarium. 



24. One of the zooecia and adjoining parts of same, xso. 



25. Vertical section of same, xis, showing the comparatively loose tabulation ot the two 



sets of tubes. 

 Upper third of the Trenton shales at St. Paul. 



Figs. 26 to 32. ASPIDOPORA PARASITICA Ulr 255 



26 add 27. Portions of a tangential section, xis and X50, with few cystiphragms and zooecia 

 very slightly larger than usual. 



28. Vertical section of same specimen, xis, showing entire thickness. 



29. Surface of same, xg. 



30 to 32. Tangential and vertical sections, xis, and the surface xg, of a thicker zoarium. 

 Lower third of the Trenton shales, Minneapolis and near Fountain, Minn. 



