Structure of Fossil Calcispongice. 29 
original tri- or quadriradiate spicules which leads, in all in- 
stances that I have examined, to the branched, forked, and 
other forms that resemble the spiculation of a Lithistid sponge, 
especially after the slice has been reduced to the lowest degree 
(that is, to semitransparency). Hence, whenever I have been 
so fortunate as to see even one undoubted tri- or quadriradiate 
of a Calcisponge, although, as before stated, it may have dis- 
appeared in the subsequent grinding, I have felt as convinced 
that the fossil was a Calcisponge as that the fantastic forms 
which accompanied it were spurious ; so that now when I come 
toa perfect tri- or quadriradiate of the kind mentioned, I stop 
grinding and mount the specimen for preservation and more 
deliberate examination. 
Process of Grinding down a Slice of a Calcareous Fossil 
for Microscopicol Kxamination. 
Take about one part of half-dry Canada balsam, and place 
it on the centre of a glass slide; heat it until melted over a 
spirit-lamp with about half an inch vertical flame, moving 
the slide backwards and forwards to prevent the latter from 
cracking ; add two parts of shellac ; and when the whole has 
bubbled up, stir it with the point of a needle so as to mix 
well, and spread it altogether over a little more of the glass 
than the size of the slice to be reduced. 
Previous to this, cut off with a watch-spring or very fine 
saw fixed in an iron bow-frame (all of which may be obtained 
from an ironmonger at a very small charge) the slice to be 
ground down; and if there be much siliceous matter in the 
fossil, the saw (which is very cheap) may be sacrificed by the 
addition of emery powder and water to the groove, as this 
accelerates the cutting. (Of course where a machine with 
horizontal turning-wheel is possessed, such as is used for 
cutting siliceous fossils, flint, &c., this is the quickest and 
most economical way to obtain the “ slice,’’) 
Having thus obtained it, so far prepared, rub one side (viz. 
that to be examined) down to scratchless smoothness on a 
schoolboy’s slate or very fine honestone with level surface, to 
effect which it is absolutely necessary that all the materials 
should be entirely freed by washing from every particle of 
emery or siliceous mineral that may happen to be present ; 
otherwise the calcareous surface. will become almost irre- 
mediably furrowed. 
Next dry the slice on a tin or paper tray placed inside the 
fender by the fire, where it can remain until the next part of 
the process is completed. 
