They had now reached the beach, and Agnes was in such high spirits, that, though she was encumbered with her large basket, she could not refrain from running backwards and forwards several times, just as we often see little dogs do, who never seem thoroughly to enjoy a walk unless they are permitted to make it twice or three times as long as it ought to be. Agnes ran round a projecting cliff so that her mother lost sight of her. She soon, however, came running back with two or three Cockle-shells in her hand. “Look mamma!” cried she, “what I have found!” “Nothing very remarkable, certainly,” said Mrs. Merton, smiling; “for I believe the cockle-shell is common on the sea-beach in every part of the world. Yet something interesting may be told even of this common shell. In the first place it is what is called a bivalve, that is, the shell is in two parts, or valves, like those of the oyster and the scallop, the two parts being united by a hinge, formed by two projecting teeth in the centre, and two side teeth.” “But what do you call teeth, mamma!” “Look, here are two projecting parts with a hollow part between. The projecting parts are called the teeth, and you see they are so placed that the teeth of one valve fit into the hollow part of the other. The creature, which is something like an oyster, and is eaten, can open and shut these valves at pleasure, and it can push out a long elbow-like part of its body and spring forward to a considerable distance when it wishes to leave the sand and return to the sea. Look, too, how delicately this valve that you have found, is ribbed, and observe the form of the shell. You see it bears some resemblance to a heart, and hence the scientific name of the genus is Cardium, which signifies a heart.” [Illustration: _Fig. 28._ WHELK (_Buccinum undatum_). ] Agnes now picked up another shell, and her mother smiled when she discovered that it was a Whelk, or Buckie. “My dear Agnes,” said she, “you certainly cannot boast of finding any very rare shells in your travels; for the whelk is nearly as common as the cockle. However, there is a material difference between them, for the whelk, or buccinum, is a univalve, that is, its shell is only in one part, like that of the snail. Look at this shell, and you will perceive a curious little notch at the lower end; and when there is this mark we know that the animal inhabiting the shell is carnivorous, that is, it lives on other creatures of its own kind. The common garden snail, which, you know, lives on vegetables, has no notch.”