SEA-SNAILS AND SEA-SLUGS. 21 1 



I have dealt at such length with the Limpet, because its 

 structure will enable us to understand the other mollusks we 

 have to mention, widely as they may appear to differ in the 

 forms of their bodies and shells. The Limpet's shell is a low 

 cone, and the shell of a Whelk is a greatly elongated cone, 

 coiled spirally upon itself ; the animal adapting itself to that 

 form. 



In addition to the Common Limpet (Patella vulgata) we 

 have the Smooth Limpet (Patella pellucidd), which must be 

 sought at low-water on the borders of the laminarian zone. It 

 feeds upon the Great Oar-weed, and a peculiar variation will 

 be found between the specimens feeding on the smooth flat 

 fronds and those feeding on the great stems. The shell of the 

 first is coloured a pale brown, pellucid as its specific name 

 suggests, the apex set very far forwards, and from it there start 

 backwards from three to six exceedingly fine radiating lines of 

 a dazzling brilliant blue. The specimens that live upon the 

 Oar-weed's stems look entirely different, for the shell becomes 



SMOOTH LIMPET. SMOOTH LIMPET, THICK VARIETY. 



thickened, and consequently much more opaque, and its shape 

 alters to enable it to sit close on a rounded surface. It was 

 formerly considered a distinct species, and was named Patella 

 Icevis. So, too, the little Tortoise-shell Limpet (Acmcea testu- 

 dinalis}, changes its form when feeding upon the leaves of the 

 Grass-wrack (Zoster a marina), and has then had the name of 

 Acmcea alvea bestowed upon it. 



There are other forms of Limpets (though not species of 

 Patellidae) to which we wish to refer, but we are getting far 



