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MUSEUM BULLETIN NO. 5. 
very different structure. The inner zone seems to consist of 
a tube with a definite wall, this tube being divided by deeply 
concavo-convex sac-like transverse partitions which have the 
appearance of the tabulae of corals. These tabulae seem to be 
convex upward, or at least they occupy that position in specimens 
found embedded in an upright position in the strata. In sections, 
the centre of this tube is open and filled with transparent calcite, 
or often empty, while around this space, close to the wall of the 
tube, is an area with numerous incomplete tabulae or cystose 
diaphragms (Plate II, figures 1, 2; Plate IV, figures 2, 4). This 
central tube, therefore, corresponds to the whole section of 
B. nodulosa Billings, as shown by Nicholson in figures 2 and 3 
of Plate VIII, of the publications cited above, but in B. nodulosa 
there is evidently much more of the cystose tissue than in the 
present species. This axial tube is nearly central in position 
in most of our specimens and is of variable diameter in pro- 
portion to the total diameter of the fossil. In one good section 
it is 3 mm. in diameter, and the total diameter is 14 mm. In 
another it is 5 mm, of a total diameter of 24 mm. In other 
forms it seems to occupy a much larger proportion, as in 
Plate I, figure 2. 
Outside the axial tube there is a zone which in the best 
specimens is filled with clear calcite or is hollow, while in others 
it is filled with a very fine-grained brownish lime-mud containing 
more or less clear calcite. None of the sections show any trace 
of structure in this zone, and there is nothing to indicate that it 
ever contained any continuous skeletal structures, though it is 
very possible that at intervals it was crossed by some sort of 
supporting processes (See Plate II, figures 1 and 2; Plate IV, 
figures 2, et al). 
The outer zone consists of a number of concentric sheaths 
traversed by radial canals. This structure is well shown in 
the best preserved of the specimens (Plate II, figures 1,2). 
The radial structure is well shown in several figures, partic- 
ularly in Plates II and III. The appearance produced is that 
of the radial septa of corals. That these are not septa, but 
radial tubes with intervening pillars is, however, shown both by 
sections and by weathered specimens. For instance, figures 
