Sea- Shells and their Occupants 149 



mature life, when the Helcion invariably transfers its place of 

 abode to the lower parts of the stalk and finally to the root of 

 the Laminaria, which are quite destitute of iridescence, these 

 blue lines disappear or become much less marked." 



To watch the development of a snail from the egg is of the 

 greatest interest. Egg-capsules of the whelk, &c, should be 

 taken home and placed in a basin or bell glass of sea-water 

 for observation. The shell is always present at birth. Its 

 shape should be carefully noted, for in many species remark- 

 able changes take place. To mention two only. The cowry 

 in the young condition is a distinctly spiral shell ; as it 

 approaches maturity the spire becomes completely hidden 

 beneath layers of shelly matter : the common limpet has at 

 first a nautiloid shell. We believe that we are correct in 

 remarking that in this, perhaps the commonest of our shells, 

 the transition stages leading up to the well-known adult form 

 have not as yet been observed. 



Notes will be given in our September issue on a sponge 

 (Cliona) which bores minute holes in shells, especially oysters. 

 It should be remembered, however, that certain mollusca also 

 bore circular holes in oyster and other shells. Nassa and 

 Murex are special enemies of the oyster and it is stated 1 that 

 " Purpura lapillus prefers Mytilus edulis to any other food, 

 piercing the shell in about two days' time by its powerful 

 radula, which it appears to employ somewhat in gimlet fashion. 

 If Mytilus cannot be procured it will eat Littorina or Trochus, 

 but its attempts on the hard shell of Patella are generally 

 failures." 



The appended plates with descriptions should materially 

 assist the young collector in the identification of his captures. 

 For the most part, only the commonest species have been 

 figured. The rock-borers or stone-piercers (Pholas, &c.) and 

 the edible species (cockle, winkle, scallop, mussel, &c.) will be 

 illustrated and described in a future number. 



1 " Cambridge Natural History." " Molluscs and Brachiopods," p. 60. 



