28 LITTORINID^. 



sionally of a \vhitisli cast) ; its outer or free margin is 

 not concave, but diagonally rectilinear. The throat is 

 smooth, always dusky, and generally almost black, with 

 a narrow zone of white near the anterior extremity. Irish 

 specimens are said to attain to the length of three-eighths 

 of an inch, but the majority of our English examples only 

 measure a quarter of an inch long, and are a third or a 

 fourth less in breadth. 



The animal has a black head and muzzle ; its tentacula 

 are pale, and on each side of each tentacle runs a dusky 

 line. The foot has dusky, almost black sides, and is 

 bordered in front by a white band ; its disk is nearly 

 white. 



On the very edge of the high-tide mark, and often at 

 considerable distances above it, where only the dash of the 

 spray can moisten it with sea water, we find this pretty 

 little raollusk assembled in myriads in the crevices of 

 rocks, on most of our rocky shores all round Britain and 

 Ireland, so generally distributed, indeed, that to enu- 

 merate localities would be superfluous. There are a few 

 suitable places, where notwithstanding it is either absent 

 or very local, as on the rocky coasts of the Isle of Man, 

 the shores of Kent, Sussex, &c. 



It is distributed all round the coasts of Europe, and 

 extends throughout the Mediterranean, always preserv- 

 ing the same habitat on the very edge of the sea. 



