128 The Under-Water World 



beautiful Ormers or Ear- Shells. These 

 are fished for in all the warmer seas 

 where their flesh is highly esteemed. 

 The " mother-o '-pearl " of the inside of 

 their shells is used for various decorative 

 purposes. 



The Top Shells (Trochidce and Turboni- 

 dee) introduce a feature characteristic of 

 many univalves. This is the " oper- 

 culum," a usually spherical cap of horny 

 material often reinforced with a layer of 

 carbonate of lime and which acts as a 

 door. This part of the mollusc may 

 weigh several pounds and present 

 gorgeous colourings. In fact, the " cat's 

 eye ' J brooch, so popular in Victorian 

 days, was manufactured from the oper- 

 cula of a species inhabiting the Indo- 

 Pacific Ocean. 



The River Snails (Vivipara), abund- 

 antly represented in the Thames, are 

 interesting in that the young are hatched 

 within the parent shell. The closely 



