Now you will understand what we shall see, and are ready for the answer to our question. You never find live clams crawling about the sand, because they live buried in the mud.
Now let us put on our boots and look about on the surface of the wet mud. Do you see ahead of us those little jets of water come spouting up into the air as if squirted out of tiny syringes? Every one of these little jets is thrown up by a soft clam, which lies perhaps several inches deep in the mud, with its siphon stretched up to the surface and held full of water, waiting for the tide to come in and refresh it. When it feels the jarring of our footsteps it squirts the water out; and you must dig deep and fast if you want to catch it. This is what those men are doing out there on the flat—digging out clams with long spades, and filling their baskets for market. Thousands of little ones lie in the mud, not yet big enough to eat.
The soft clam is a shapeless sort of mollusk, with a thin chalky shell, not at all pretty; but the hard clam, or quahog, is thick-shelled and regular in outline; and in an end-on view takes the shape of an ace of hearts, like the Venus-shell, or the cockle, which is so commonly eaten in Europe. This species likes much deeper water than the soft clam, and is gathered mostly from boats, by a kind of rake; but we shall no doubt find a few up here. Do you see that scratch in the mud? It looks like a trail, and there at the end is the traveler himself, standing upright in the mud like a half-buried wedge.
This shows another difference between the two clams; for while the soft clams and their relatives, such as the pretty razor-fish, and the "old maid" of English bays, never leave the burrow where they begin life, the quahogs slowly wander about all the time. As for the scallops, they fairly skip and jump.
What are scallops? Well, we shall hardly see much of them, for they live in deep water; but their half-shells are to be seen cast up everywhere, for they also are bivalves. Our common ones are usually about the size of a silver dollar, and fan-shaped, the thin shell ribbed like the sticks of a fan, and the margin crinkled, and they are variously colored, but mostly in tints of reddish and yellow.
Several small bivalves and sea-snails may be added to our collection from this uncovered bay-bottom, and here and there spaces are fairly sprinkled with little blackish fellows about the size of hazelnuts. When we have gathered a handful we shall find we can sort out three or four kinds.
A very curious denizen of the tide-flats of our Southern States is the pinna, a large bivalve with thin horny shells shaped like a slightly opened fan, which lies deeply buried, point down. The edges of its shell come just at the surface, and are exceedingly sharp, so that barefooted persons have to be very careful how they step where pinnas are common, as on the Gulf coast of Florida, and it is no wonder the people there call them razor-fish. Lying there in the mud, with its shells parted, and a current of water always sucking down what we may call its throat, it forms a regular trap for little fishes and other small creatures. The instant one swims between the shells, they close and the unfortunate curiosity-seeker finds himself in a prison from which there is no escape.
When a young pinna settles down in its place it at once anchors itself to some rock or fixed thing below it by throwing out from near its lower, narrow end a bunch of very strong threads, which hold it down so firmly that it takes a very hard pull to tear them away. This anchor-cable is called a byssus.
A short distance from us a narrow stream wriggles through the salt marsh, and we can get into a rough little boat and paddle down toward that old wharf whose weedy piles are covered with interesting things, which we may examine now that the ebbing tide has left them uncovered for a few hours. The peaty banks, with their growth of harsh salt-grass and algæ, will keep our eyes busy as we float along the black and winding creek.
Now we shall get acquainted with some of the crabs. Look sharply down into the water and you will see the large "blue" crabs which we buy in the market, and eat, swimming near the bottom or crawling over the mud near the banks. There is one, now. He doesn't look very blue, nor very appetizing, does he? His back is brown and muddy, to be sure; but his big claws and lower plates have much more blue upon them than has any of the other large crabs, and so he gets the distinguishing name.