MOLLUSCA— COCKLE.. PHOLAS. 769 



THE COCKLE i 



Of the cardium, or cockle tribe, there are more than fifty spec.es; some 

 or other of which are to be procured on the sandy shores of all the known 

 seas. They are mostly found immersed a few inches deep in the sand. In 

 size, the different species vary considerably, some being five or six inches in 

 diameter, and others not more than half an inch. The cockle has a tolera- 

 ble degree of locomotive power, in consequence of its triangular yellow foot, 

 which is conspicuous on the shell being opened. With this foot it can also 

 draw into threads its glutinous matter, and thus in a manner anchor itself 

 on the spot that it has chosen for its residence. The opening of the shell 

 is protected by a soft membrane, which wholly closes up the front, except 

 in two places, at each of which there is a small, yellow, fringed tube. 

 Through these tubes the animal receives and ejects the water which conveys 

 nutriment to its body. 



THE CARDIUM EDULE, OR COMMON COCKLE, 



Which is the species most common in England, has a grayish shell, some- 

 what heart-shaped, with about twenty-eight flattish ribs, transversely striated, 

 with recurved imbrications. It is a wholesome and pleasant food. Lobsters 

 and crabs lie in wait for an opportunity of thrusting in a leg or a claw, 

 when the cockle is open, in order to prey on the included animal; but it 

 often happens that the younger ones of those crustaceous animals, not being 

 sufficiently hard to withstand the violent snapping of the shells of the larger 

 species when they close, are deprived of the limb. 



THE PHOLAS. 2 



Of all animals of the shelly tribe, the Pholades are the most won- 

 derful. These animals are found in different places; sometimes cloth- 

 ed in their proper shell, at the bottom of the water; sometimes con- 

 cealed in lumps of marly earth ; and sometimes lodged, shell and all. 



1 The genus Cardium is characterized by a shell equivalve, subcordiform, with protube- 

 rant beaks ; valves dentated, or plicated on their internal margin; hinge with four teeth 

 in each valve, of which the two primary ones are approximated and oblique, and two late- 

 ral distant ones. 



2 The genus Pholas has the shell bivalve, equivalve, transverse, gaping on each side 

 with several accessory pieces, either on the hinge, or below it; inferior margin of the 

 valves bent outwards ; animal destitute of a tubular sheath, projecting anteriorly, two 

 united tubes, often surrounded by a common skin, and posteriorly, a short, thick, musculaj 

 foot, flattened at its extremity. 



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