164 POPULAR BRITISH CONCHOLOGY. 



This is not exactly the case with the species of our coast, 

 which have the whorls almost as closely connected as the 

 Turritellcs, or any other turreted shells. They have a 

 lengthened spire of many whorls, which are girt at regular 

 intervals hy circular ribs, indicating regular periods of growth. 

 At these periods, the mantle ceases for a time to deposit its 

 shelly secretion in advancing layers, and accumulates all its 

 stores upon the edge of the circumference, which becomes 

 thickened and rolled up, as it were, so as to form an external 

 varix or ridge ; this accomplished, the onward growth is 

 continued, till, arriving at the corresponding ridge of the 

 preceding whorl, the animal is reminded that it is time to 

 make another. Thus, from ridge to ridge, and from whorl 

 to whorl, proceeds the gradual formation of the tapering 

 column. The foot is angular and semicircular in front, 

 slightly sinuous at each side, and terminating in a pointed 

 arch behind; the head has two long, pointed tentacles, with 

 eyes at their base ; operculum horny and spiral. Some spe- 

 cies, if not all, live by preying on marine creatures smaller 

 than themselves. About the apertures of some dried speci- 

 mens may be seen a purple stain, indicating that the Scalane 

 secrete and exude a briUiant purple dye. 



The shells of our species may be thus distinguished : — 



