10 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I39 



Many of the thick diaphragms also display centrally located pores 

 that do not penetrate through to the distal sides of most of the thickest 

 diaphragms. Laminae of the diaphragms generally stop abruptly at 

 the pores without changing direction or flexing, so that the pores have 

 no lining or apparent influence on the structure of the diaphragms. In 

 other thick diaphragms the laminae trend in a proximal direction in 

 varying amounts and there is a noticeable decrease in diaphragm thick- 

 ness approaching the pore. The pores in the outer region also differ 

 from the central pores of the inner region of the exozone by being 

 consistently smaller in diameter. In addition to the pores, mesopore 

 diaphragms and walls in the outer region contain small, dark, sub- 

 spherical to elongated cavities formed by the concentric arrangement 

 of laminae about imaginary centers. These cavities seem to be ar- 

 ranged at random in the walls and diaphragms. 



Zooecia. — In the outer region of the exozone, undistorted wall 

 structure of adjacent zooecia is rarely seen because of intervening 

 mesopores and acanthopores. Zooecial boundaries are well defined, 

 dark, slightly serrated lines or zones in two dimensions, formed by 

 the abutting ends of laminae from adjacent zooecia. In walls formed 

 by a zooecium and adjacent mesopore, or by adjacent mesopores, 

 boundaries are more coarsely serrated and are commonly discontinuous 

 along their length. 



Diaphragms are not present in most zooecia and not more than 

 two were seen in any one zooecium. If present, diaphragms are very 

 thin, planar to slightly curved, and extend distally into the zooecial 

 wall. Single, hollow, subspherical cystlike structures occur in the 

 zooecial voids of a very few zooecia, more commonly in the monticules. 

 The cyst walls are thick and are constructed of laminae that merge 

 with the laminae of the zooecial walls. Irregular spinelike proc- 

 esses are common in the zooecial walls in the thick-walled outer 

 region. These mural spines have their origins at or very near the 

 zooecial boundaries and trend in general toward the zooecial voids at a 

 high angle to undisturbed laminae in the walls. Zooecial wall laminae 

 surrounding the spines are flexed about the spines in a series of ir- 

 regular superposed cones and some of the laminae are pierced. The 

 spines extend far enough to cause inflection of the walls but none were 

 observed to break through the wall laminae and stand in relief in the 

 zooecial voids. The cores of the spines appear structureless or hollow. 



Tangential View. — In tangential sections passing through the 

 outer region of the exozone, zooecia range from irregularly elliptical 

 to subcircular to petaloid in cross section. Major axes of the ellipses 

 are approximately parallel to branch length. The rare petaloid ap- 



