1 8 Oliver and Salisbury. — On the Structure and 
x i*2 mm. wide; in Lagenostoma Lomaxii the corresponding dimensions 
were 0-75 mm. x 0-7 mm. 
The cells which formed the wall of the lagenostome were in lateral 
continuity by about a third of the depth of their radial walls, thus leaving 
their major exterior portions free. It is due to this peculiarity, together 
with the obliquity of the sections, that the misleading appearance of a two- 
layered wall is due. This feature, strikingly shown by the preparations 
R. no (PI. II, Fig. 14, Ig.) and R. 117 (Fig. 18, lg.), might readily give rise 
to the view that the lagenostome was a two-layered structure. The radial 
dimension of these cells ranges from 26 to 30 /x ; the tangential horizontal 
is approximately 26 /x , and the tangential vertical 39 /x. 
In form, the cells are roughly hexagonal as seen in tangential view. 
They were arranged in successive tiers with their shorter sides directed 
upwards and downwards. The wall seems to have 
been continued right up to the mouth without marked 
change in character, unless perhaps the appearance 
of thinning shown by preparation R. 117 (PI. II, 
Fig. 18) at the top of the lagenostome be not merely 
the result of post-mortem shrinkage. 
A great feature of the cells of this layer was the 
elaborate, tracheid-like sculpturing of their walls — 
well shown in specimen R. 115, 1 (PI. II, Fig. 20, lg.), 
and, on a much enlarged scale, in the adjacent text- 
figure (Text-fig. 6). These sculpturings, which were 
of the scalariform or slightly reticulated type, reach 
a maximum development on the tangential wall, i. e. 
the wall in contact with the integument. Other characteristic sections of the 
lagenostome are shown by specimens R. 111, R. 114, and R. 116 (PI. I, 
Figs. 7, 2, and 6). These figures also illustrate the marked tendency* of 
this cell layer to undergo degeneration prior to fossilization. Thus in 
preparation R. m (PI. I, Fig. J,lg.) the outer walls of one layer and the 
inner walls of the adjacent layer have perished, whilst in R. 116 (Fig. 6 , lg.) 
solution has proceeded still further, so that little remains beyond the 
common radial walls of the obliquely cut cells. 
Though these tracheid-like elements of the lagenostome were of 
delicate construction, they must, in virtue of their sculptured walls, have 
had a marked capacity to resist crushing forces. Occasionally the lageno- 
stome is slightly retracted from the micropyle in consequence no doubt of 
post-mortem shrinkage (e. g. Fig. 7), but in all cases that have come under 
observation the form of the lagenostome is perfectly preserved. 
The floor of the lagenostome did not consist of differentiated, sculp- 
tured cells, but was occupied by a pad of soft tissue which readily under- 
went displacement, leaving a clear orifice — well shown in preparations R. 117 
Text-fig. 6. Sketch 
slightly diagrammatic, 
showing the sculpturing 
on the cells of the 
lagenostome. 
