4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I39 



In the inner region of the exozone, the mesopores are beaded (series 

 of rounded chambers). This beading is produced by the mesopore 

 walls curving transversely to the axis of the mesopore to form a 

 diaphragm. The succession of longitudinally and transversely lami- 

 nated structures along the walls and diaphragms is interpreted to 

 indicate deposition from both sides of longitudinal as well as trans- 

 verse structure throughout the inner region. Thus, at least a part of 

 the depositing tissue of the mesopore remained behind the diaphragm 

 and within the chamber being formed. The pore in the center of the 

 mesopore diaphragm presumably would be necessary to allow the soft 

 parts within the chamber to communicate with the outside environ- 

 ment. There is no indication as to whether the soft parts in the 

 mesopores during the formation of the inner region consisted of any- 

 thing more than a depositing tissue or mantle, but the distal diaphragm 

 would have acted, temporarily at least, as a covering for any soft parts 

 within the last chamber. Continuity of laminae from the distal side of 

 a diaphragm to the wall of the succeeding mesopore chamber implies 

 that at least the proximal part of the chamber was formed as the dia- 

 phragm developed (see middle diaphragm of the inner region in the 

 upper mesopore of figure i). For a more complete discussion of 

 figure 1 see species description. 



The thick-walled outer region of the exozone contains transversely 

 laminated structure in the walls of zooecia and mesopores and longi- 

 tudinally laminated structure in the thick diaphragms. The mesopores 

 in this region are not beaded. The pattern of continuity of the laminae 

 of walls and adjoining diaphragms (fig. 1) indicates deposition was 

 limited to the outer surface of the walls and diaphragms, con- 

 temporaneous deposition of laminae taking place on the outermost 

 surfaces of the zooecial wall, around the median line or boundary to 

 the mesopore wall, and back to the distal side of the diaphragm. There 

 is no evidence that deposition occurred on the proximal side of the 

 diaphragm within the mesopore chamber. 



The formation of the diaphragms in the inner and outer regions 

 of the exozone is quite different. Diaphragms in the inner region were 

 formed by continued distal growth of mesopore walls that merely 

 curved through an angle of 90 degrees to form transverse structures. 

 Diaphragms in the outer region were formed by an additional, trans- 

 versely oriented sheet of depositing tissue that was continuous with at 

 least the depositing tissue of the mesopore side of the walls and ac- 

 tively deposited calcite at the same time that the mesopore walls were 

 being formed. This transverse sheet of tissue apparently had no 

 counterpart in the inner region of the exozone. 



