6 
MUSEUM BULLETIN NO. 5. 
of the cylinder, the tabulae or diaphragms are mostly well preserved 
and apparently in their natural positions. In the enlarged, bulbous 
part, all of the diaphragms are broken and none extends across 
the full width of the bulb. This portion of the tube is filled with 
the same limestone in which the fossil is embedded, whereas, 
in the cylindrical part lower down, where the diaphragms are 
unbroken, the chambers are, generally, filled with crystalline 
calcite. Beginning at the bulbous end the inner tube shows, 
first, 4 mm. with cystose tissue, such as is seen around the inner 
part of the tube in some sections. Then 39 mm. in which all 
diaphragms are broken and the filling is like the matrix. Next, 
20 mm . of clear calcite filling. Next, three unusually deep chambers 
(18 mm. in all) filled with limestone matrix. Then follow 33 
mm. in which the diaphragms are rather close together (twelve 
chambers in the interval), and the filling material is all calcite. 
Next a single deep chamber (6 mm.), filled with matrix, then three 
(6 mm. in all) with calcite, one partially empty. Next two (9 mm.), 
empty except for a lining of calcite crystals. Then three (13 mm.) , 
with clear calcite. Then a deep one partially filled with clear calcite 
and partially with matrix. The filling with limy mud seems 
to have taken place after the death of the organism and after 
it had fallen from its erect to a horizontal position. The cham- 
bers with unfractured walls and diaphragms were evidently cut 
off from the supply of mud, and the filling consists of such mate- 
rial as could be filtered in in solutions. The mud-filled parts 
must, on the other hand, have had openings by which rather 
coarse material could enter, and that these openings were acci- 
dental and not natural is indicated by the fact that the dia- 
phragms or side walls are seen to be fractured in most cases. The 
supply of mud does not, however, seem to have entered directly 
from the outside to the chambers which it now fills, but has been 
conveyed along the “empty zone*’ surrounding the tube. 
This zone is filled with clay, and served to feed mud into 
the inner tube through any fractures which might be present. 
In most cases this zone is filled with clear calcite (as in figure 
1, Plate III, and figures 1 and 2, Plate IV, for instance), but 
in such cases there is often another and outer zone mud-filled 
(figure 2, Plate IV). The explanation of these “empty” zones is 
