102 THE MOLLUSCA 



other decomposing animal matter ; and to see these huge shells 

 moving about amongst the coral reefs by a succession of little 

 leaps and bounds as they search for food is a most curious sight. 

 The Fountain Shell of the West Indies, which belongs to this 

 family, sometimes weighs as much as five pounds, and is nearly 

 a foot in width. As it becomes old the mollusc fills up the apex 

 and spines of its shell with solid shelly matter. 



The largest British univalve is the Whelk, some species of 

 which, found on the coast of Scotland, attain a length of from 

 six to seven inches. All the Whelks are carnivorous in their habits, 

 and are most voracious creatures, much dreaded for their depre- 

 dations in oyster beds. Purpura lapillus, commonly called the 

 Dog Whelk, is perhaps the worst offender ; but Buccinum undatum, 

 the Common Whelk, and Nassa reticulata, also sometimes called 

 the Dog Whelk, and one or two other species, are all accredited 

 with being partial to an oyster lunch. The Whelk first fixes 

 itself firmly by means of its great foot on the shell of its victim, 

 and then proceeds to drill a neat hole in it with the file-like end 

 of its radula. Through this hole the mollusc inserts its long, 

 flexible proboscis, and actually sucks the oyster out of its shell. 

 The Whelk family by no means confine themselves to oysters, 

 but devour limpets, periwinkles, top-shells, mussels and other 

 bivalves, in the same manner, or they will eat any dead animal 

 matter that comes in their way. 



Purpura is one of the commonest Gastropods of the seashore. 

 Quantities may be seen clustered together on nearly every 

 breakwater when the tide is out. The shell is exceedingly variable 

 in colour, ranging from pure white through deepening shades of 

 yellow and brown to chocolate or even black ; while many are 

 banded with contrasting shades of brown, grey, or bright orange. 



The Sea Snail (Natica), common on sandy shores, is also of 

 cannibalistic habits. The thick, round, smooth shell, tinged with 

 pink and splashed with brown, of this little mollusc is known 

 to most visitors to the seaside. The Natica is quite blind, and 

 lives partly or completely buried in the sand down by low-Water 

 mark. The foot is most remarkably developed, and when pro- 

 truded swells out to such an extent all round that the shell all 

 but disappears within its folds, and it seems almost impossible 

 that the great, fleshy mass can ever return whence it came. 



