PLATE XVII. 
IGS IEhOISs so MIRSOMR VPA TNBTD AL, WME are aretstaresa)ssaye osteo vele als) lors roierevs co ofelstesedayorafololotelaveieverateleeie) sinielsereleisie(ere 258 
land 2. Two tangential sections prepared from the same example, X18. The first illus- 
trates the fully matured condition, the second an earlier level in the zoarium. 'Tren- 
ton shales near Fountain, Minn. 
3to5. Three portions of a large vertical section of the same, <18, showing the variable 
disposition and appearance of zocecial diaphragms. 
6. Portion of another vertical section of same X18. Mus. Reg. No. 5993. 
7. Surface of same, <9, 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. 
Migs 9GO 2) SM ESOMR Yar AN ((P)ISPENOSIAG TENS Js cre ohclolefesevateteratnletaiayeleletela/stefatsl slekeha(scolelatepitaVexersiayol=el-yeleislntaistedetelsts 259 
9. Surface of well preserved example, showing the round form and regular arrangement of 
the zocecial apertures, and the strong acanthopores; 9. 
10 and 11. Tangential section, *18, and parts of several zocecia *50. 
12. Small portion of a vertical section, X18, Showing unmistakable cystiphragms in the 
lower half. Other parts of the same section are like figs. 3 and 4 of this plate. 
Middle third of the Trenton shales at St. Paul and Minneapolis. 
Figs. 13 to 21. ASPIDOPORA ELEGANTULA, D.SP.--eseec cee ce cece ccc cece ee eee cnet eset tees eens tens 256 
13. A fine example of this species on the surface of which an intermittent second layer of 
zocecia was forming; natural size. 
14. One of the areas of the secondary layer, <9. = 
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, *9. 
19. Tangential section of one of the layers of same, <18. 
20. Parts of several zocecia of a tangential section, <50. 
21. Several zocecia and mesopores as seen in a vertical section of one of the layers, X18. 
Galena shales, Kenyon, Minn. These two specimens were collected by W. H. Scofield 
and kindly presented by him to the author. 
Figs. 22 to 25. PRASOPORA LENTICULARIS, 0. SP...-.-s seen cecee cee cece eee eee e ete e eee cee eee secu ence 253 
22. Upper surface and sectional view of an example of this species; natural size. 
23. Two portions of a tangential section of same, X18, 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 zocecia and adjoining parts of same, 50. 
25. Vertical section of same, X18, showing the comparatively loose tabulation of the two 
sets of tubes. 
Upper third of the Trenton shales at St. Paul. 
Figs. 26 to 32. ASPIDOPORA PARASITICA UIT... .... 06 .e cece cee e eee eect tere ee eee ene e eee eee en eens 25% 
26 add 27. Portions of a tangential section, x18 and <50, with few cystiphragms and zocecia 
very slightly larger than usual, 
28. Vertical section of same specimen, X18, showing entire thickness. 
29. Surface of same, x9. 
30 to 32. Tangential and vertical sections, <18, and the surface 9, of a thicker zoarium. 
Lower third of the Trenton shales, Minneapolis and near Fountain, Minn. 
