When you put a conch shell to your ear, it's not the sea you hear, it's the rushing of your own blood.

J. Charles Boehm knows a lot about shells. "You could put a box over your ear, and it would do the same thing, make the sound waves reflect back on the inner ear," he says.

But it's still a romantic business, the business of shells. For Boehm, it's a living, and a good one. He has a shell shop, La Boutique de la Mer, in Palm Beach, and now he has a special exhibit of shells at the Mineral Kingdom, 3251 Prospect St. NW, through Feb. 12. The shells are displayed in cases along with jewelry that complements them in lovely, subtle ways.

Ever since Jackie Kennedy put a nautilus design on her note paper, shells have been increasingly chic. Far cheaper than jewelry but often far more beautiful in their purity and simplicity, they are shown off on Lucite stands, on silver trays, in glass cases. Specialty shops sell them in ocean resort cities everywhere.

As an inventment, they are something of a nightmare. Shells that once were all but priceless because of their extreme rarity can be bought easily today, thanks to modern diving techniques and an expanding market. Take the precious wentletrap (from an Old Dutch word meaning sprial staircase), a chaste white series of whorls, crisply ridged, that once brought $400,000 or more. Now you can get one for $16.

Once they were so valued that the ingenious Chinese made rice paper imitations. Today those antique imitations are worth much more than the shells.

"The golden cowrie used to go for $3,000," said Boehm. "They're $250 to $450 now. They come and go every season depending on conditions on the sea bottom."

Pink corral is now an endangered species, its harvesting banned by some governments. The chambered nautilus is also being monitored, though Boehm says he has waded through Pacific waters up to his hips in the big shells.

Where do shells come from? That's a story in itself.

"All the best stuff comes from the Indo-Pacific area. You deal with all kinds of people. I do have two or three divers in Key West who go after specific shells for me.Thoroughly unconventional types, conches, they don't have a phone, you have to go down there and talk to them and be patient."

Say you want a rare spondylus Americanus, an American spring oyster, diet variant, which means it ate the wrong things and grew into a spectacular orange-striped shell with rose-colored spikes all over it. After two or three weeks the diver might find one, clean it with dental picks, an excruciating job, especially when done to the tune of a half-case of beer, and sell it to you. If he likes you.

"I have a friend who lives on a boat, the White Trash, off St. Thomas, and his dinghy is named the Soiled Dove," said Boehm. "He calls me Cap. I asked for some West Indian fighting conch shells, and he said, 'Okay, Cap,' and came back with a trayful. I paid him $1 each."

Some shells are displayed in their natural colors. Some are dipped in muriati acid, which exposes the silvery nacreous underskin. Some are covered with scrimshaw or other carvings, usually not an improvement.

"If you get a live shell with the animal still in it, don't boil it, because that makes little hairline cracks in the surface. The thing to do is to freeze it and then take out the animal."

Do they know how talented they are, the creatures who create these shells, the clambered nautilus who builds greater mansions every year, the trochi and spondyli who paint wondrous murals on their tiny walls? Do they guess how we sigh over their works, and stroke the sleek surfaces, and treasure them? h