The bar is said to be from the wreckage of Capt Kidd's ship, the Adventure Galley
Underwater explorers in Madagascar say they have discovered treasure belonging to the notorious 17th-Century Scottish pirate William Kidd.
A 50kg (7st 9lb) silver bar was brought to shore on Thursday on the island of Sainte Marie, from what is thought to be the wreck of the Adventure Galley.
The bar was presented to Madagascar's president at a special ceremony.
US explorer Barry Clifford says he believes there are many more such bars still in the wreck.
Capt Kidd was first appointed by the British authorities to tackle piracy but later became a ruthless criminal and was executed in 1701.
'Scepticism'
"Captain's Kidd's treasure is the stuff of legends. People have been looking for it for 300 years. To literally have it hit me on the head - I thought what the heck just happened to me. I really didn't expect this," Mr Clifford said.
"There's more down there. I know the whole bottom of the cavity where I found the silver bar is filled with metal. It's too murky down there to see what metal, but my metal detector tells me there is metal on all sides."
The BBC's Martin Vogl tweets that there is much excitement in Madagascar about the discovery and Mr Clifford's team has no doubt that the discovery is genuine.
Barry Clifford led a team which discovered the suspected treasure
Soldiers watched over the silver at a ceremony attended by the president and diplomats
The team believes the bar, marked with what appears to be a letter S and a letter T, has its origins in 17th-Century Bolivia.
It believes the ship it has found was built in England, however there is bound to be scepticism and calls for more proof that the bar was linked to Capt Kidd, our reporter says.
One option would be to take samples of wood from the ship to analyse, he says.
The location of the ship, thought to have sunk in 1698, has been known about for many years but the silver bar was only discovered earlier this week.
Mr Clifford said that while diving in the wreck, his metal detector picked up signals but it was too muddy for him to see anything.
UK ambassador to Madagascar Timothy Smart, who attended the ceremony, said he hoped that Mr Clifford's latest discovery would raise Madagascar's profile as a tourist destination.
The plan is to exhibit the bars in a museum.
Who was Captain Kidd?
He is thought to have been born in Scotland's Greenock or the Dundee area in about 1645.
He was appointed by the Crown to tackle piracy and capture enemy French ships, but turned to piracy himself.
In 1698, he looted the Armenian ship the Quedagh Merchant, which was apparently sailing under a French pass.
There have been numerous searches for William Kidd's loot
He appeared before the bar of the House of Commons before his execution
The Quedagh Merchant had been carrying satins, muslins, gold and silver.
Unfortunately for Kidd, the captain of the ship was an Englishman, and it is thought that a large amount of the cargo belonged to the British East India Company.
Capt Kidd was captured and brought back to London. He was found guilt of piracy and the murder of one of his crewmen during a row in 1697, and sentenced to death.
During his execution in Wapping in 1701, the first rope put around his neck broke, so he was strung up a second time. That rope also snapped, but the third one held.
Afterwards, his body was dipped in tar and hung by chains along the River Thames to serve as a warning to would-be pirates.
Legend had it that Capt Kidd hid much of his loot, which has prompted numerous treasure hunts around the world and inspired author Robert Louis Stevenson when writing Treasure Island.
