PLATE XxX. 
Figs. 1 to 9, 138 and 14. MONTICULIPORA ARBORBA, D. SP....eeee ses e cece ee eee cette tee eee ence ee ean es 220 
1. Peripheral part of a vertical section *18. 
2. Several tubes from the axial region of same X18, showing the presence of cystiphragms in 
even this portion of the zoarium. ; 
3. Transverse section from the center to the periphery of a branch <18, proving the presence 
of cystiphragms throughout. 
4and 5. Fully matured portion of a tangential section X18 and a small part of same X50. 
6. Shows the appearance at a slightly lower level than fig. 4. 
7. Small portion of the surface of the specimen represented by flg. 8; <9. 
8 and 9. Two fragments of the natural size exhibiting a difference in the prominence of 
the monticules. 
Galena shales near Cannon Falls, Minn. 
13 and 14. Tangential and vertical sections of a form of thespecies from the Trenton at 
Burgin, Ky.; *18. 
Figs. 10 to 12. MONTICULIPORA (?) CANNONENSIS, I. SP..-.- 2. eee eee ee cette eee eer eee eee e ne eeee ees 221 
10 and 11. Vertical and tangential sections x18. 
12, One zocecium 50. 
Galena shales near Cannon Falls, Minn. 
Figs. 15 to 21, HOoMOTRYPA CALLOSA, 1. SP... ..- sees sees ce eee eee eee ee cee cece eet e ee cece e ee eeee 243 
15 and 16. Tangential section*18 and a small portion of same 450, of a specimen from the 
Galena shales near Cannon Falls. 
17. Vertical section of same 18. 
18 and 19. Peripheral and axial portions of a vertical section 18, prepared from a specimen 
from the Trenton at Burgin, Ky. 
20 and 21. Tangential section of same X18 and X50, differing slightly from that of the Min- 
nesota form. 
Figs. 22 to 27. ATACTOPORELLA RAMOSA, D.SP....- ssc ceee ee eee scence te eee rete e eee cence ee cees 226 
22. Two portions of a tangential section 18, exhibiting differences that depend upon the 
varying depth at which the section passes through the zoarium. 
23. Small portion of same more highly magnified. 
24. Axial region of a transverse section 18. 
25. Vertical section X18, showing the continuance of the series of cystiphragms into the 
axial region. 
26 and 27. Two specimens of the natural size. 
Upper third of the Trenton shales near Cannon Falls, Minn. 
Figs 28 to 33. HOMOTRYPA SIMILIS Foord*.........- 20s eee e rece cee ee cence eee e nets eee een eeeee ees 242 
28. Portion of the peripheral third of a transverse section x18, Cannon Falls. 
29, Vertical section of an authentic Canadian example of the species x18. 
30. Two portions of a tangential section of same *18. 
31 and 32. Vertical and tangential sections of a Minnesota specimen, *18. 
33. Surface of another specimen from this state <18. 
Trenton limestone Ottawa, Can., and upper part of the Galena shales near Cannon 
Falls, Minn. 
*The systematic position of this species is doubtful. Though falling in a loose way under Homotrypa some of its char- 
acters are so peculiar that it can in no wise be regarded as a true representative of the genus. ‘Thin sections are suggest- 
i vely like those of Homotrypella instabilis and in some features also simulate those of Eridotrypa mutabilis. 
