262 



Shell Life 



Common Whelk 



curved broad ribs which are traversed by the spiral 

 lines. This species is widely and plentifully distri- 

 buted all round our 

 islands, on all kinds 

 of bottoms and at all 

 depths of water. A 

 creature found under 

 so many conditions 

 should show a great 

 amount of variation, 

 if there is anything 

 in the views already 

 set forth in these 

 pages, in which it has 

 been claimed that the form and substance of the shell 

 lias relation to the habitat. Littoral species, we have 

 pointed out, like the Winkles and the Purple have 

 thick solid shells to withstand the hammering of the 

 waves and the pounding of stones ; and all those 

 individuals who do not develop a thick shell will be 

 broken up and destroyed, leaving only those with 

 thick shells to survive and perpetuate the species. 

 What is true of the species living under one set of 

 conditions differing from another species living under 

 other conditions, applies also to the individuals of a 

 species that yet live under varying conditions of 

 depth, climate, and surroundings. The var. liioralis 

 lives among stones and on mud in the upper part of 

 the laminarian zone, and consequently is less elongated, 

 broader, more strongly ribbed than the var./rauto.sa 

 that dwells on hard ground in the coralline zone in 

 the Hebrides, etc. Then the var. paupercula owes 

 its dwarfed and puny proportions to living in brackish 



