PLATE XXI. 
Figs. 1 to 7. CONSTELLARIA VARIA, 1. SP.... cece eee e cece eee e eee cence es tee tne cere cent tere ceseneree 311 
1. Surface of a mature example, ¥9, with wide interspaces and correspondingly narrow 
zocecial apertures. 7 
2. Surface, 18, of another example showing a less matured stage than fig. 1, the inter- 
spaces being thinner and the zowcial apertures larger. 
3. Tangential section, X18, showing appearances immediately beneath the surface’of an old 
_ specimen. At deeper levels the walis are thinner and the interspaces narrower. 
4. Small portion of preceding, 50, with two of the minute mural tubuli. 
5. Vertical section of an average specimen, X18. 
6and7. Two fragments of the natural size, one very small, the other of medium dimen- 
sions. 
Galena shales near Cannon Falls, Minn. 
IMS eh WO) IPL INP rohe Cop ectopic N Tope ONGWNE GI yas nocaacqonndoncudpacdop aGd0 ocdaDcbOUScaEaoD AaodDs 314 
8. An unusually wide fragment of the natural size. 
9. Surface of same, <9. ; 
10. Two portions of a tangential section, X18, the upper illustrating the appearance just 
beneath the surface of a mature example, the lower at a deeper level. 
11. Vertical section of same, 18. 
12. Central portion of a transverse section, *18. 
‘Pierce limestone”, Murfreesboro, Tenn. 
Figs. 13, 14, 20 and'22. NICHOLSONELLA PONDEROSA? Ulrich............0..-ececeecec cece cence e eres 316 
13. Two portions of a tangential section, <18. In the original the details are obscure and 
it is probable that the interstitial dots are too numerous and small. 
20. Small portion of the peripheral part of a vertical section, X18. The structure is but 
illy preserved in these sections, 
14. Two portions of a tangential section of another specimen, <18, the upper immediately 
beneath the surface. = 
22. From the peripheral part of a transverse section of same, X18. 
Lower third of the Trenton shales, Minneapolis. 
Figs. 15 to 19 and 21. NICHOLSONELLA LAMINATA, DL. SP...-.0---..0-- eee eee e eee ee sce c ee tesetseeee 315 
15. Tangential section of specimen in an unusually good state of preservation, X18. 
16 and 17. Portions of same 50. 
18 and 19. Under side of a fragment, nat. size, and the upper surface <9. In this specimen 
the mesopores are shown much more Clearly than in others. 
21. Small portion of a vertical section, 18, passing through one of the macule. 
Middle third of the Trenton shales, Minneapolis. 
Figs. 23 to 40. TREMATOPORA ? PRIMIGENIA (and varieties) UIrich............. see ee cence eee eee ee 309 
23 to 27. Fragments of the typical form. 
28 and 33. Original type of 7. ornata and surface of same x18. 
29. A large specimen of var. spinosa ; 30, a smaller and better preserved fragment; 35, sur- 
face of the latter, *9; 36, small portion of same <18. 
31. Surface, <9, of an average example of the typical form. No attempt has been made to 
draw the small acanthopores. 
32. Surface of specimen with acanthopores unusually abundant and inflecting the zowcial 
apertures, X18. The specimen is peculiar also in having many of the mesopores open. 
34. Original of fig. 26, x18, (var. ornata) with spines and occasional open pores in the inter 
spaces. 
37. Tangential section, X18, from aspecimen whose surface is drawn in fig. 32. 
38. More common appearance of typical tangential sections, X18. 
39. Small part of preceding 50. 
40. Vertical section of basal expansion, X18. It is attached to a crinoid column and shows 
how the tubes grew into the depressions between the rings and failed to attain ma- 
turity. 
Middle third of the,Trenton shales, Minneapolis, 
