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Basket Shells

No mollusk of equal size is more in evidence on the Atlantic coast. Especially does it throng the muddy shores where by the emptying of streams the water is somewhat brackish. On mud flats, exposed at low tide, they may be seen by thousands, scrambling nimbly about doing scavenger duty. A dead crab or fish calls together an army of them, which soon dispatch the ill-smelling object. Obliged to find live prey, they bore the shells of bivalves, and are even suspected of eating each other at a pinch. The largest is an inch long.

Habitat.--Nova Scotia to Florida.

The Lash Nassa (N. vibex, Say) is the handsomest of the basket shells. Strong longitudinal ridges, set far apart, cross the fine spiral ones, forming nodules at the shoulder of each whorl. The shell is heavy; the toothed lip thick; the callus of the columella spreads out into a broad flat triangular patch on the body whorl. The colouring is chestnut and white, in bands and clouds. Length, 3/4 inch.

Habitat.--West Indies, to Chesapeake Bay and Cape Cod.

The Lean Nassa (N. mendica, Gld.) has a slender, strongly sculptured shell, of fine revolving lines crossed by remote, prominent ridges, broken by the sutures. The exterior is marked with pale brown; the interior is white. Length, 1/2 to 3/4 inch.

Habitat.--Puget Sound to San Diego, Cal.

The Fat Nassa (N. perpinguis, Hinds) resembles N. fossata in its stout figure, and in other particulars, but it is smaller throughout. The surface is finely cancellated, and marked with chestnut. The lining is bright orange. It never reaches an inch in length.

Habitat.--Southern Califorina.

The Slate Nassa (N. tegula, Rve.) is dark gray in colour, with a pale band just below the noduled shoulder of the whorl. The aperture is lined with smooth white enamel. Length, 3/4 inch.

Habitat.--Southern California.

The Netted Dog Whelk (N. reticulata, Linn.), found on sandy shores from Norway to the Mediterranean, has been the subject of much study. It is an inch or more in length, a robust mollusk in a solid, cancellated shell, brownish white, often banded with chocolate below the suture. Back from its thin edge the lip is thickened and toothed; the columella is smooth with a widespread callus. There is considerable variability of sculpture from fine to coarse.

At the recess of each tide this mollusk buries itself in the sand in a slanting position, its lurking place betrayed by a little hillock. It gets into lobster pots for the sake of the bait.

Buried in the sand at the bottom of an aquarium, these mollusks will always respond to one stimulus unless it comes just after a hearty meal. Scraps of meat, fresh or stale, make an irresistible appeal. Bones with particles of meat adhering are soon buried by the mollusks. Simply passing a bit of meat over the sand, then withdrawing it, served the same purpose of drawing the animals, so strong is their sense of smell.

The eggs of this Nassa are laid on seaweed. The capsules are like flat purses, the size of a spangle, on short stems. These are attached to the stems of seaweeds, and overlap each other in a single row. The young escape from the capsule through a hole at the top. They have ciliated lobes by which they swim. The antics they cut are amusing to watch, and seem to be merely playful, but are probably a struggle to resist capture by swarms of infusorians.

The robust N. reticulata does great damage in the parcs of Arcbachon, where the famous French oysters are raised. Like our destructive "drill," the Nassas of all ages bore the oyster shells, and suck out the soft parts of their helpless victims. The tide sweeps, in bringing fresh thousands of these destroyers, so that combating them is a long, unequal fight.

Fortunate for our oyster growers the dog whelks of the Atlantic prefer dead fish to live oysters, so they are a negligible, even though numerous, element in the fauna of the coast. Other mollusks are victims of the dog whelks' patient boring. They are even suspected of cannibalism. Finally, in their decline, small hermit crabs tear them from their shells, and take possession, each making a meal of the dismembered body of its victim.