PLATE XII. 
PAGE. 
Higs: 1-0 4,30\and 31. HSCHAROPORA ANGULARIS, 1. SDise cc occ’ «jee vic) leie/alele «\e1s\eis «/e\e1si=\nai*) + \0\n\0\~\= 168 
land 2. A small specimen of natural size and the greater portion of it <9. 
3and4. A large specimen of the natural size and a portion of the upper half of its sur- 
face X18. 
30 and 31. Vertical and tangential sections, x18. 
Trenton limestone, Minneapolis. 
MIPS D012 04 SCHAAR OPORANSUBR RE CIA MU lirtirpstatarerstcteretetatslers)sjcleleloteteteslelstetonvayelsteneleferareteepstetetstetTetetata(elelstels 168 
5 to 17. A series of specimens, most of them above the average in size and the four last 
with from one to three rows of monticules. 
18 and 19. The central and basal portions of the original of fig. 9, <9. 
20. Part of same, X18. The characters as shown in this specimen are to be regarded as 
typical for the species in its younger stages. 
21. Surface of another small example, X18, with the marginal rows of zocecia unusually 
conspicuous. 
22. Surface of the basal third of the original of fig. 15, 18. The features here presented 
are unusual. 
23. Surface of the upper part of the original of fig. 16, x18. 
24. Surface of the original of fig. 17, x18. In the specimen the zocecial apertures manifest 
a tendency to arrange themselves in an obscurely pinnate manner. 
25. Tangential section of an example corresponding to fig. 9; *18. 
26. Tangential section of a specimen of the size of fig. 8, or a trifle larger; x18. 
27. Tangential section, X18, showing the appearance just beneath the surface of an old 
example. ; 
28. Vertical section of several zocecia prepared from an average specimen, *18. 
29. Transverse section of same X12. 
Middle third of the Trenton shales at St. Paul and Minneapolis. 
