But besides the fenestrae, there is, in some cases, a small central opening which does penetrate through the wall.
Fenestrae 7, with fissures radiating to a rounded central opening.
Fenestrae three, large, the lowest the largest, arranged in a triangle.
Five fenestrae below each mouth; numerous branching bands on the back of the cell.
The selective pressures both for the inception and continued expansion of the fenestrae differed from group to group.
All the windows (fenestrae) were small (Fig. 65), hardly larger than three feet by two.