PLATE XXvVIl. 
Figs. 1 to8. BArostOMA WINCHELLI Ulr 
1,2and 3. Vertical sections X18, of a young, medium, and an old specimen. 
4and 5. Tangential section, X18 and <50, of the same specimen from which was prepared 
the vertical section shown in fig. 3. 
6. Tangential section of a young specimen 18. 
7and 8. Tangential section of the var spinuloswum 18 and X50. (See also plate 26.) 
Middle third of the Trenton shales, Minneapolis and St. Paul. : 
Migs woo b.wATOSTOMA (MININESOLEINSE il siSp sete siciestelacloweletoricieie ete leieleinioremcteetrst siesta aieteteie eievereneieiste 297 
9and 10. Portions of a tangential section 18 and x50. 
11 and 12. Peripheral and axial regions of a vertical section prepared from the same speci- 
men as the preceding, 18. 
13. The peripheral part of a zocecial tube with fewer diaphragms than usual, 18. The true 
average for the species is intermediate between this and fig. 11. 
14 and 15. Portions of two tangential sections, X18 and 50, in a different state of preser- 
vation than figs. 9and 10. (See also plate 26.) 
Middle third of the Trenton shales, St. Paul and Minneapolis. 
Wigs. 416; CORT es ATOSTOMAN (A) DECIPLEINS ste iSpseperereateacteterteiseiecistlete acisielesierereteiens esas tet taietsreleiers 298 
16. Small portion of a vertical section X18. 
17 and 18. Tangential section X18 and X50. In some parts of this section certain small 
acanthopore-like dots are distinguishable usually about midway between the angles. 
They are dark and scarcely half the size of the smallest shown in fig. 10. 
19. From the axial region of a transverse section X18. 
Lower half of the Trenton shales, Minneapolis. 
Jess PAN ENA Din enous a WE OhoTpano DOG) Wenomdsadseensoeooos aobacos ddsudcabueahouadens 319 
20. Tangential section x18. In this section the cells here drawn as open are filled with 
matrix, while those shaded are occupied by clear calcite. The smaller of the latter 
have the appearance of mesopores; on the other hand, since the preservation of the 
fossil is not favorable, it is possible that they represent acanthopores. 
21. Vertical section of the upper extremity of same beyond the foreign body, 18. 
Middle third of the Trenton shales, St. Paul. 
Migs. 22ande23, pun PTOMR PAT INEOR MIS Mess pers niaee cysiaa aire cette a aise ee ete etet ele cieseates a ote taere 317 
Tangential and vertical sections X18. 
Lower third of the Trenton shales, Minneapolis. 
Wigs. 2an dio; UEPMOTR PA AOR VU OSA. MSS) acianceocinice ea aciecn eee eerie ier elites erate 318 
Tangential and vertical sections X18. 
Galena shales, Decorah, Iowa. 
Miger26/and 2 MONOTR PAN (? CHa TM TRS) CUM ULADAY My SP) ites ateieiceteisielelaleie cinteeieisteteletelsieiseiteialcicists 307 
Tangential and vertical sections x9. Beneath the first the stracture of the wall is shown X35. 
Upper part of the Galena shales, Goodhue county, Minn. . 
Figs. 28 and 29. MONOTRYPA MAGNA, N. sp 
Vertical and tangential sections <9. 
“Lower Blue” limestone at Dixon, Ill. 
