1ft 



sienna colour between tlie pallial line and the maro-in of 

 the shell (PI. I., fig*. F). This, however, is absent in some 

 specimens, and does not occur in P. opcrcidaris. 



GENERAL ORGANISATION AND MANTLE. 



It is diflficult to kill and preserve the specimens with- 

 out a considerable amount of contraction and distortion 

 taking place. Crystals of mentliol dropped into the sea 

 water in a small dish containing a specimen of P. 

 opercidaris produce the best results witb the least 

 retraction of the tentacles and mantle. For P. ma.ximvs, 

 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 Perenyi's fluid or Pikrosulphnric, 

 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 bodv wall, tbe 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 fPl. II., fig. 1, 

 Mn.). These lobes enclose the pallial cavity, in which 



