GASTEROPODA. 237 



ever, informs us that it was considered necessary to 

 extract the dye as soon as the animal was captured, 

 as it was discharged if allowed to remain untouched. 

 The smaller shells were crushed, but from the large 

 ones the animal was extracted. They are said to 

 bury themselves in the wet sand of the shore. 



The spinous projections, often of great length and 

 slenderness, with which many shells are armed, may 

 possibly be intended for a defence against violence, 

 but the species which are most remarkable for them 

 are themselves of carnivorous propensities. That 

 these, however, do not always preserve them, we 

 have already seen, for even the thick and stony 

 processes of the gigantic Conchs of the West Indies 

 (S trombus)* are crushed in the jaws of the Logger- 

 head Turtle. 



As the outer surfaces of shells are often marked 

 with bands and spots of various colours, while the 

 inside shews an uniform pearly tint, it may not be un- 

 interesting to say a word on the mode in which these 

 respective hues are produced. In shelled Gastero- 

 poda, the mantle generally covers the whole of the 

 parts usually contained within the shell ; its outer 

 edge is thickened into a glandular collar, which is 

 the source from whence the shell's increase in size 

 is derived. The mantle is studded with glands that 

 secrete the colouring matter of the various hues and 

 patterns that mark the shell. "When the animal 

 wishes to enlarge its dwelling, this thick collar is 



* The ancient Greek name of some spiral shell, from rrfaftw t strobeo, to 

 twist. 



