240 PATELLIDJS. 



men in the north of England. Sea-fowl of all kinds 

 are also fond of the limpet. The bill of the oyster- 

 catcher is said to be admirably adapted for forcing it 

 from the rock ; and the pious Derham tells us that 

 " the Author of Nature seems to have framed it purely 

 for that use/'' Something must now be said for the limpet 

 itself, as well as about its persecutors. It appears from 

 the experiments of Beudant to have an unusual capa- 

 bility of living in fresh water. This may be accounted 

 for by its littoral habit, which exposes it to rain and 

 the efflux of streams into the sea, as well as to the con- 

 tinual percolation of fresh water which takes place on 

 shingly beaches. The animal is occasionally monstrous. 

 Fischer noticed a limpet on the French coast which had 

 the left tentacle branched or double, with two eyes at 

 its base. The shell is as much entitled to the name 

 polymorpha as to that of vulgata. In the ' Zoologist ^ 

 for October 1860 will be found an excellent remark by 

 Mr. Norman, as to the variation of its form resulting 

 from habitat ; and I cannot do better than give it in 

 his own words. '' It will be found to be a general rule 

 with regard to the limpet, that the nearer high-water 

 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.^^ 

 In the intermediate space, and under local conditions, 

 other forms of course occur, which partake of some of 

 the above characteristics in a modified degree. Speci- 

 mens which I found in a particular spot at Lerwick 

 were excessively thin, and as if they were exfoliated, 

 probably owing to a deficiency of calcareous material. 

 One shell from Balta Sound is of an extraordinary 

 thickness and weight : it had been inhabited by a 

 colony of the burrowing cirriped^ Alcippe lampas ; and 



