PLATE XXVI. 
PAGE. 
Migs: Leto) 6: BY THOPORAEHERRICKIAU I sacnstaa sensltt cei OO. Coan ora ee ee once 263 
1. Vertical section <18, showing slight irregularity in the growth. 
2and 3. Tangential section 18 and a portion of same X50. 
4and 5. A large and an average sized specimen. 
6. Surface of the smaller <9. 
Middle third of the Trenton shales at Minneapolis. 
Hig Sai tOj9 se BYTHOPORASALCICORNIS; Na Sprccce stat ccae a eee ene eee eC eee each oe eee ee 264 
7 and 8. Two specimens of the natural size. 
9. Surface of the larger one x9. 
Upper third of the Trenton shales near Cannon Falls. 
Migs 10016) = HOMOTRY PEELE A (i) SUBGIRA CIGEIS M.S Daueeasticntaiic cen seas eseaciene ara en taeecls 230 
10 and 11. Two tangential sections X18, showing slight differences. 
12. Vertical section <18.. The structure is almost entirely destroyed and only the direc- 
tion of the tubes is to be made out with any certainty. 
13 and 14. Two'specimens, the second a little above the average in size, 
15 and 16. Surface of the larger specimen *9 and *18. 
Middle third of the Trenton shales, St. Paul. 
Bigs. Leto! HRI OTRYP- ATE SGA sins) SD iota cci a Steere ee eee ere eee omen ae eee ian eee eee nee 266 
17. A group of fragments as they appear mounted on a slide. 
18 and 19. Two of them x9. 
Upper part of the Galena shales near Cannon Falls. 
Wigs. 20, 21, 29and 30. ERIDOTRYPA MUTABILIS, Var: MINOR, D. Var.......02.ccee sce seccee eres eees 266 
20. Three fragments of the natural size. 
21. Surface of one of them x9. 
29 and 30, Vertical and tangential sections *18. 
Galena shales near Cannon Falls. 
Migs:122 to28 31,132.  HRIDOTRY:PA:MUDABELIG. Me ISpeecm on cmaseiise cic ciecas ceiiceneciachinee mee eee 265 
22. A specimen of the average size. 
23. Large example. 
24. Surface of an old example presenting an unusual appearance, “18. 
25. Surface of the original of fig. 23, x18. The figure includes one of the macule and ex- 
hibits the most common appearance of these. ; 
26and 27. Tangential section x18 anda portion of same <50; represents an average fully 
matured condition. 
28. Vertical section of the same specimen X18; shows a superficial layer of zooecia growing 
in a direction opposite to the first set. 
31 and 32. Vertical and tangential sections <18, of an old specimen which has grown irreg- 
ularly causing many interspaces and thus unusually numerous and large mesopores. 
Galena shales, Goodhue county, Minn. 
Migs IB OVS. ATOSTO MAU TVAEN CHEE oO Lee arte (etre rata eieie telare lols tatereisiaiera ate best sraclec is rieieie ee teie eteleielersteietere 
33. A specimen of the usual diameter. 
34. Another, of large though not uncommon size. 
35. .An average example of the var. nodosa. 
36. Surface of a fully matured example x9. 
37. Surface of the original of fig. 38 x9 and X18. (See also plate 27.) 
Middle third of the Trenton shales, Minneapolis and St. Paul. 
Wigs) 3856040. -BATOSTONEA MININESODENGE Met S De oyerc css stevie ityel-lelerseietele et ete viele «fe ieleless ctelatarayate eset 
383 and 39. Two specimens, the first small, the other of the average size. 
40. Surface of the larger specimen, which is in an excellent state of preservation, <9, show- 
ing the granulose walls. (See also plate 27.) 
Middle third of the Trenton shales, Minneapolis. 
295 
