350 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
sienna colour between the pallial line and the margin of 
the shell (Pl. I., fig. F).. This, however, is absent in some 
specimens, and does not occur in P. operciularis. 
GENERAL ORGANISATION AND MANTLE. 
It is difficult to kill and preserve the specimens with- 
out a considerable amount of contraction and distortion 
taking place. Crystals of menthol dropped into the sea 
water in a small dish containing a specimen of P. 
opercularis produce the best results with the least 
retraction of the tentacles and mantle. For P. maaimus, 
the mixture of Lo Bianco, spirit glycerine and sea water, 
floated gradually over the water in the vessel containing 
the specimens, gives very good results. When narcotised 
sufficiently in this way, the animal should be placed in 
5 per cent. formalin, and may remain in this until 
required, the muscle, however, becoming somewhat hard. 
The animal should be removed entirely from the shell 
by separating the mantle lobes carefully with the handle 
of a scalpel and cutting the attached portions of the 
adductor muscle, and can then be pinned down and 
examined under water. 
For serial sections, the smallest specimens obtainable 
should be dropped into Perenyt's fluid or Pikrosulphuric, 
and fixed according to the usual directions. These fluids 
dissolve also the calcareous part of the valves so that the 
specimens are ready for embedding after dehydration. 
When removed from the shell it will be seen that the 
viscera and body proper are hidden between two folds of 
the body wall, the mantle or pallial lobes, which are 
almost of the same shape and size as the valves of the shell 
to which they were attached by muscles (Pl. IL, fig. 1, 
Mn.). These lobes enclose the pallial cavity, in which 
