20 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 



face sufficiently flat to acconmiodate the increased 

 size of the shell, which seems to induce the animal to 

 seek a smoother surface nearer low water, where the 

 rocks are kept well polished by the constant action 

 of the sea and debris Avashed against them. This 

 tendency has been well observed by the Hev. A. M. 

 Norman, quoted by Dr. Jeffreys : "It will be found 

 to be a general rule with regard to the limpet, that 

 the nearer high-^vater mark the shell is taken, the 

 higher-spired, more strongly ribbed, and smaller it 

 will be ; and that the lower down it lives, the flatter, 

 less ribbed, and larger it becomes." * 



* Brit Conch., iii. 2i0. 



