PLATE XXVII—Continued. 
Stictofora Gilberti. 
Page 90. 
See Plate 28. 
Fig-. 20. A fragment of a frond, natural size. 
Fig. 21. An enlargement of the adherent surface of the cells, the mesotheca having been removed. (X 6.) 
Fig. 22. A transverse section, showing the form of the branch and the upright portion of the cell tubes. (X 0-) 
Fig. 23. The lower portion of the figure (a), showing the natural surface of the frond, and on the left 
hand, the part adjacent (£>), shows the cell tubes, the outer covering having- been broken 
away ; the upper right hand corner (e), shows the inner aspect of the opposite face. (X 6.) 
Fig. 24. A longitudinal natural section enlarged, showing the form and manner of growth of the cell tubes, 
the strongly annulated appearance caused by the intercellular vesicular structure, and the 
striations on the interior of the cell-walls formed in the course of growth by the lunate denti- 
culation of the aperture. (X (1.) 
Fig. 25. A transverse section enlarged, showing the form of the branch and the interior character of the 
ridges separating the ranges of apertures. (X 0.) 
Fig. 25. One of the cells greatly enlarged, showing more distinctly the character of the lunate denticula- 
tion. (X 40.) 
Fig. 27. A transverse section enlarged to six diameters. 
Fig. 28. An enlargement of the surface of a specimen, which has been much macerated, the cell apertures 
having the appearance of the fenestrules of some form of Fenestella, and the intervening space 
resembling the branches and dissepiments. (X 6.) 
Fig. 29. The inner portion of the coencecium enlarged, showing the irregular vesiculose structure between 
the cells. (X 6.) 
Fig. 30. An enlargement of a portion of the surface of a branch, showing the strong lunate denticulations, 
the extremities of which in the process of growth, form the parallel striations along the interior 
of the cell tube. (X 6.) 
Fig. 31. An enlargement of a portion of the surface of a branch near the margin, where the cell apertures 
are pustuliform. (X 6.) 
Fig. 32. An enlargement of a portion of a branch where the exterior has been removed, showing the form 
and arrangement of the basal portion of the cell tubes as they rise from the mesotheca. 
Fig. 33. A portion of the surface of a frond enlarged, showing strong denticulations and a sharp depression 
along the middle of the ridge separating the ranges'of cell aperatures. (X 6.) 
Fig. 34. An enlargement of a portion of a frond near the spreading base. (X 6.) 
Fig. 35. The mesotheca enlarged, showing the radiating longitudinal lines, which mark the direction of 
the cell tubes, and the transverse arching undulations of growth. (X 6.) 
Upper Helderberg- group, halls of the Ohio river. 
