NO. 5 ORDOVICIAN BRYOZOA — BOARDMAN 21 



Diaphragms vary considerably from zoarium to zoarium in spacing, 

 parallelism, thickness, and curvature. They range from parallel and 

 widely and evenly spaced to cystoidal, compound, and closely and 

 irregularly spaced. If present, marked thickening or closeness of 

 spacing of a few diaphragms in a zooecium occurs in similar posi- 

 tions in most of the zooecia of a section. 



In longitudinal view, the acanthopores that are offset and inflect 

 zooecial walls are visible within zooecial voids for short intervals in 

 areas of the section that happen to be immediately adjacent and 

 running generally parallel to the zooecial walls. The offset acantho- 

 pores arise from zooecial walls and are attached to the walls along 

 their entire length by ridges of skeletal material. In thicker sections 

 and polished sections these offset acanthopores appear to vary in 

 length, unlike most acanthopores that are within zooecial walls and 

 run throughout the width of the exozone. The offset acanthopores 

 begin at the inception of the exozone in some zoaria or well within 

 the exozone in other zoaria. The offset acanthopores may end well 

 within the exozone, or may continue to the distal ends of the zooecia. 

 Commonly, the offset acanthopores end at the outermost diaphragm 

 and thus are not seen on the exterior in many areas of a zoarium. 



Mesopores are very rare. Early mesopore chambers are beaded. 

 Distally the beading is lost and mesopore diaphragms are thick and 

 closely and regularly spaced. Laminae of diaphragms in mesopores 

 and zooecia are continuous distally with laminae of surrounding walls. 



In tangential sections, zooecial walls appear integrate or amalga- 

 mate. The amalgamate appearance is generally more pronounced in 

 areas of a thin section that contain offset acanthopores. In zooecia 

 appearing amalgamate in tangential section, the amalgamate band 

 appears granular and its margins merge gradually into the laminated 

 appearance of the inner part of the walls. Zooecial linings are easily 

 distinguishable by a darker shade and sharp contact with the re- 

 mainder of the zooecial wall. 



In areas of tangential sections that do not contain offset acantho- 

 pores, acanthopores are dark and are concentrated in zooecial corners. 

 A few occur between corners and are centered on zooecial boundaries. 

 In areas of tangential sections that contain pronounced inflecting of 

 zooecial walls by offset acanthopores, these offset acanthopores are 

 generally between zooecial corners, and the numerical concentra- 

 tion of all acanthopores is nearly twice that of areas without inflec- 

 tion. Offset acanthopores always have an extension of skeletal ma- 

 terial connecting the acanthopores and zooecial walls. 



