Shrimps are caught with a fine-meshed trawl net, drawn by a boat or by horse and cart, or with push nets or hose nets. One great objection to shrimping is that the shallow, sandy areas on which it takes place are much frequented by young fish—particularly dabs, plaice, soles, whiting and codling. Owing to the small mesh of the shrimp trawl, these small fish are captured in large numbers and are generally dead or dying when discharged from the net. Generally, the shrimps are separated from the small fish by riddling, and the smaller shrimps are then separated from the larger ones by a second riddling process, and are returned to the sea. The shrimps are thrown into boiling salt water, rapidly stirred for a few seconds, and spread out on the deck to cool. From three to four hauls are made per day, a good day’s fishing consisting of from 30 to 40 quarts of shrimps. Large numbers of shrimps are potted. The other important group of shellfish is the mollusca. Molluscs, i.e. “soft creatures,” are essentially soft, mobile animals, protected by shells. They are classed as bi-valves, for example oyster and mussel, and uni-valves, for example limpet and whelk. There is no real difference between a bi-valve and a uni-valve, for what appear to be the two shells of the bi-valve are really one shell divided into two parts by a line of soft, uncalcified material which forms a hinge between the two halves of the shell; this hinge tends to keep the shell open, but the muscular action of the living animal inside keeps it closed when required. With the exception of the mussel, very few shellfish actually live on the shore between the tide marks. Most of the seashore shells are brought by the sea from animals that lived in from 10 to 20 fathoms of water. The cockle lives buried in the sand, about an inch below the surface. The oyster lives on stones and shells below low-water mark. All molluscs are attached tightly to the shell at one or two points, and cannot be removed from the shell alive. In the case of the bi-valves the animal is attached to the two shells by a muscle which draws the two valves of the bi-valve together. When this muscle is relaxed, for example in normal circumstances, when feeding at the bottom of the sea—the shell remains open. Some shellfish—notably the scallop—actually swim by opening and shutting the two valves of their shell. The most important uni-valves are the periwinkle, the limpet and the whelk. Uni-valves possess a well-marked head and neck, a pair of eyes and a mouth. They are remarkable for the possession of a tongue, formed like a ribbon rasp, furnished on its upper surface with a large number of small teeth. The number and arrangement of these teeth differ in different species. With this ribbon rasp the uni-valve, for example a dog-whelk, can rasp a hole through the shell of an oyster and feed upon the contents.