PLATE XIX. 
Figs. 1 to 9. HOMOTRYPA MINNESOTENSIS UlP.... 2.00.0 see e eee e ence cen e eee eee teeecscceccnces 235 
1to3. Vertical, transverse and tangential sections X18, of a specimen having the walls in 
the peripheral region thicker than usual. Mus. Reg. No, 5970. 
3a. Small portion of a tangential section of an example of the var. montifera, x50. Base 
of the upper third of the Trenton shales at St. Paul. 
4and5. Tangential and vertical sections of an average specimen, X18. 
6. The peripheral part of two zocecial tubes, X18, more closely tabulated than usual. Mus. 
Reg. No. 5970b. 
7 and 8. Two examples of the natural size. The end view under the latter shows the ex- 
ceeding narrowness of the peripheral region. 
9. Surface of the original of fig. 7, <9. 
Lower third of the Trenton shales, Minneapolis. 
SOLOW Cou O MO TR WAU EEXSLTTS eI Te oyeteonereteretetelel etek slat slates eferelatieletsletelessteleleteteteteyalen-taterela isle! teteteralelstelstotsier=1< 236 
10 and 11. Two fragments of the natural size. 
12. Vertical section 18. 
13. Tangential section in a pre-mature condition, x18. 
14. Tangential section showing fully matured characters, 18. 
15. Portion of fig. 14 more highly magnified. 
16. Portion of fig. 13 more highly magnified. 
Lower third of the Trenton shales at Minneapolis. 
Figs. 17 to 20. HOMOTRYPA SEPARATA, D SP....-ccecccceccee cre coven tnccce tees sees ce ncenereeeees 237 
17 and 18. Tangential section of this peculiar species, X18,and a portion of same X50. 
19. Surface of a well marked specimen *9. 
20. Vertical section X18. Attention is to be directed to the tabulated interstitial spaces. 
Lower third of the Trenton shales, Minneapolis. 
Figs. 21 to 28. HOMOTRYPA SUBRAMOSA UIP. 2.0.0... cece. ccc cece cece teen cr secsrncscereccicressseess 229 
21. View of a characteristic specimen showing the irregular division of the branches. 
22,24 and 25. A series of three tangential sections <18, agreeing in all respects except that 
while in the first the acanthopores are numerous and well developed they are fewer in 
the second and quite inconspicuous in the third. Original of fig. 24 belongs to Survey 
Museum, Reg. No. 5980a. 
23. Small portion of fig. 22 more highly magnified. 
26. Vertical section x18, of a specimen having the outermost region loosely tabulated; very 
unusual. Mus. Reg. No. 5980b. 
27. Vertical section of a typical example, <18. 
28. Surface of an average example, showing the cystiphragms in the zocecial apertures, <9. 
Upper third of the Trenton shales, St. Paul and near Cannon Falls. 
