No parrot sits on Capt. Tracy Bowden's shoulder shouting "pieces of eight, pieces of eight," but Bowden has snatched trunkfuls from the wrecks of Spanish galleons. True to the stories, a map marked with an "X" led to sunken treasure in the waters off the Dominican Republic.

Some 300 artifacts -- diamonds, emeralds, a brass clock, gold crosses and rings, sacred medals, edgraved glass, a ship's bell, decorated pottery, and yes, peices of eight (Spanish coins) -- salvaged from the depths by Bowden -- are in an exibit opening today at the National Geographic Society's Explorers Hall, 17th and M streets NW, and ending mid-January 1982.

The artifacts are magnificently displayed. Some are in aquariums with pieces of coral and tiny goldfish. "Not just for effect," explained Peter Purpura, curator of the hall and designer of the show. "Some of these pieces haven't been stabilized, so they need the water to conserve them." t

The treasures are only part of one of the richest underwater salvages in history, still continuing. They come from two ships, the Tolosa and the Guadalupe, which sailed from Spain in 1724 carrying 1,200 immigrants, sightseers and crew, a cargo of rich personal possessions and 400 tons of mercury. The mercury, called quicksilver, was used in mining gold.

"A hurricane sunk the ships," said Bowden at a Geographic Society's luncheon. "Eight people clung to a mast for 32 days, according to old records, and were saved. Several hundred others made it to shore, but many of these perished when they ate poison fruit. The ragtag group marched around the island for many days before they found help."

Bowden found the Guadalupe first, and then the Tolosa. From archives in Seville, he knew the ships were carrying mercury.

"I had read about the ships," Bowden said, "and sure enough, there was a map in the Dominican official records marking the spots with as 'X' where they went down. Even so, we had to search quite a while before we found them."

Bowden sometimes feels as if more than luck and good seamanship guided him to the right spots."I can't explain it," he said, "and it certainly doesn't spook me or anything, but I sometimes feel as if I had been aboard that ship, in another life. When you're down in the deep, sometimes you feel as though someone's with you.

"One time I told a new diver to look in a certain place, and everyone scoffed at me. He found a great pile of pearls and jewelry. Another time one of our divers found a hunk of coral which had grown around the bottom of a box, and other pieces of timber. He kept hammering at it. When the coral broke off, there was a pile of gold coins."

Just like in the pirate stories (Bowden says he took to the seas after seeing Errol Flynn in "Captain Blood"), the treasure is divided among the divers, after half has gone to the Dominican Republic's government.

So far, Bowden has brought up very little of the mercury, because its salvage would endanger the artifacts. "But at more than $5 an ounce, it is certainly worth salvaging what remains of the 400 tons," he said.

Some of Bowden's and the diver's share has been sold at Neiman-Marcus in Texas. National Geographic helped support the exhibition. The pieces here are lent by the Dominican Republic's Commission for Underwater Archaeological Recovery and Caribe Salvage, Bowden's company.