CHAPTER XVII: THE COCKLES. HEART SHELLS 



Family Cardiid/E 



Shell regularly equivalve, heart-shaped, radiately ribbed; 

 sculpture of posterior area different from front and sides; hinge 

 with one or two cardinal teeth and two laterals on each valve; 

 ligament short, external; muscle scars squarish; pallial line sinuous 

 behind; mantle open in front; ocelli on border; siphons short, 

 fringed at tip; gills two on each side, thick, joined posteriorly; 

 foot large, sickle-shaped, without byssus. 



Free mollusks, marine or in brackish water. 



Genus CARDIUM, Linn. 



Shell globose, heart-shaped when viewed endwise; beaks 

 prominent, nearly central; ribs strong; margins of valves crenu- 

 lated. A large genus, one hundred species, of world-wide dis- 

 tribution, near low water, in sand or mud, forming extensive 

 beds in sheltered bays or estuaries. 



The Common or Edible Cockle (C. edule, Linn.) needs no 

 description in Europe. It is so extensively "raked in" for food 

 and bait from the sandy and muddy shallows skirting the British 

 Isles and the Continent as to be the most familiar bivalve in 

 fishing villages and in the city fish markets. 



The solid shells bear about twenty-five strong, rounded ribs, 

 with nodules or squamate scales, if the creature lives in muddy 

 water; if in sand, these trimmings are worn off by attrition, as 

 the mollusk moves about freely. Thrusting out the long foot to 

 its full extent, the cockle lifts itself with a quick, twisting motion 

 and flops a distance of several inches. The tip of the foot dilates, 

 forming a fulcrum upon which the muscles act in this awkward 

 mode of locomotion. 



The foot is white, the mantle yellow, fringed at the border. 

 A red band near the edge trims the yellow surface of the shells. 



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