8 AUSTRALASIAN ANTARCTIC EXPEDITION, 
individuals of the same species and different for different species. ‘These characters 
are difficult to define in words and recourse is therefore had to figures of definite districts 
of the body, of which the most useful for comparison are the ventral body wall and the 
side arms. All the figures are reproduced with the magnification. of 45, in order to 
facilitate comparisons. 
The technique of preparing the spicules for microscopic examination recom- 
mended by Blochmann is as follows :—by utilising the natural gape of the shell the 
desired parts of the body wall or of the arms may be cut away by suitable instruments 
without further damaging the specimen. Dried material is first soaked for some time 
away from air in old turpentine, and the mounting is done with gum damar. ‘The arms 
of the larger specimens are best not mounted, but examined while immersed in 
turpentine, cedar oil, or fluid paraftine, as they can then be moyed into any desired 
position. 
As material for the study of the spicules of brachiopods is not readily available 
for practice in acquiring the technique, | venture to give in greater detail the procedure 
finally adopted by Professor Kirk and myself. The part which it is desired to mount 
is first cut away, and if dried, is soaked for some time in water, and all air-bubbles 
removed under an air-pump. ‘The specimen is then, while still under water, placed 
between two stout cover glasses in the position in which it is desired to mount it. It is 
then transferred to alcohol to remove the water, two lots of alcohol being used, and then 
to clove oil. The upper cover glass may now be removed as the clove oil renders the 
object rigid in the desired position. If any air-bubbles still remain they are removed 
at this stage by the air-pump. ‘he cover-glass and object are then lifted out of the 
oil and partially drained, and the object is then slid into the desired position on a slide 
on which a bed of canada balsam and xylol has been placed, and is covered in the usual 
manner. 
There is no difficulty in mounting portions of the body wall or of the mantle 
unless these are so old as to have become very brittle, but the suitable mounting of the 
side arms of Liothyrina and Lnothyrella is not always easy, owing to the shape of these 
organs and the position of the spicules. It is best to spread the arms out so that the 
dorsal and ventral parts of the arms are separated, keeping a note of which is the 
dorsal and which the ventral side, but that sometimes proves impossible, and it is then 
necessary to rely on an optical section to separate the spicules of the dorsal and ventral 
sides of the arms. In either case the side folds of the arms which often bear spicules 
are folded against the arms, and an optical section has to be relied upon. This militates 
against clear photographic representation of the spicules. 
The punctation and shell structure of brachiopods has received renewed 
attention in recent years, particularly with a view to the use of these characters in 
classification, and rather divergent opinions have been expressed. ‘The prisms of the 
prismatic layer of the shell meet the inner surface obliquely, and trace upon it a 
“mosaic,” which varies in pattern in different species. For purposes of comparing 
