92 Canon A. M. Norman—WNotes on the 
such a species as nitida this hollow or Jumen is very manifest ; 
but in most cases the lumen is only indicated by a line seen 
along the centre of the bar, which, whether actually visible or 
not, may be called the Jumen-line. On this lumen-line there 
are often openings into the lumen, which may be called 
lumen-pores (see woodcut, line of C), at other times calcareous 
matter is heaped up along the lumen-line, so that a strong 726 
is formed. The side of the bar may be called the lateral 
line, and the poral openings usually developed upon it may 
be styled lateral lacunes*, and those at its extremity median 
lacunes. 
The great peculiarity in the structure of this group consists 
in the curious fact that, while the openings along the centre 
of the bars are simple pores or openings into the lumen, no 
lacune, whether lateral or distal, is ever formed without the 
combined assistance of two adjacent bars; and indeed in the 
posterior portion of such a species as Gattye, where several 
bars meet at one point, at that point three, or even four, bars 
seem sometimes to contribute to the building up of the circle 
of a single very small lacune. In the woodcut the semicir- 
cular hollows which break the lateral lines indicate the portion 
of as many lacunes which that line contributes to form, and 
similarly the two distal hollows indicate the share which this 
bar takes towards the structure of two of the median lacunes, 
the remaining portion of which will be supplied by a bar or 
bars which have their origin in the opposite wall of the 
zoecium. A lateral lacune therefore consists of two parts 
divided horizontally (see E), owing its origin to the lateral 
walls of two adjacent bars; while a median lacune consists 
of two vertical portions contributed by the distal extremities 
of two opposite bars F. 
‘The Cribrilinidan zocecia which are figured and described 
here were thus treated :—After being boiled in liquor potassz 
they were again boiled in water, the water poured off, and 
the shell or stone dropped into cold water, when the zoarium 
often at once detaches itself; and if it should not a slight 
pressure with a scalpel at its edge will often suffice to dislodge 
it. If this does not succeed the shell is held against the side 
of the flame of a spirit-lamp in such a way that the surface 
opposite to that to which the zoarium is attached is in contact 
with the flame, and the shell, when it is extremely heated, is 
suddenly dropped into cold water, when the zoarium is usually 
liberated ; in obstinate cases the heating has to be repeated. 
I undertook the following investigations from the desire 
* Lacuna, a space not filled up. 
