SOUTH PORTLAND — About 50 descendants of a prominent 18th-century merchant gathered Saturday at Mount Pleasant Cemetery on Cottage Road to try to solve a family mystery.

Where exactly lies the body of the family patriarch, Col. Ezekiel Cushing, who in 1738 settled in what was then part of Falmouth but is now the Bug Light Park area of South Portland?

Members of four generations of Cushing’s descendants – there are nine at this point – and their spouses watched as Glen Vaillancourt of Dig Smart of Maine operated his underground scanning radar equipment over the Cushing family plot hoping to find traces of the colonel, who died in 1765.

“There is no headstone,” said Anil Melwani of New York City, an eighth-generation descendant of Cushing who caught the genealogy bug from his mother, Jackie Gulhaugen of New York, who caught it from her father, Benjamin Cushing, who grew up on Long Island in Casco Bay.

Ezekiel Cushing was the 18th-century Maine equivalent of Inc. founder Jeff Bezos. Cushing was a prosperous owner of whaling ships and a merchant fleet that traded with the West Indies.

He moved to Maine in 1738 from Provincetown, Massachusetts, and bought up several Casco Bay islands and most of Long Island, where his descendants still own land.

Cushing was the commander of the County Regiment, a justice of the peace and a longtime Falmouth selectman. He built a home, where he entertained governors and other prominent folks, on what was then Cushing’s Point, now part of Bug Light Park in South Portland.

Melwani, who organized the radar scanning, said the family assumed that Cushing was buried at the family plot at Mount Pleasant Cemetery, where there are headstones for his first wife, Hannah, who died in 1742, and several of their children. But if not, family theory went, he might have been buried where his second wife, Mary, would be laid to rest in 1800. But Mary Cushing’s burial place is unknown.

The South Portland Historical Society has so far been unable to throw any light on the mystery.

Kathy DePhilippo, executive director of the historical society, said some records suggest that Cushing was buried at the family plot at Mount Pleasant Cemetery, which back in the 1700s was the burial ground for the Second Parish of Falmouth, now the First Congregational Church, United Church of Christ. Hannah Cushing’s grave is the oldest recorded burial at the cemetery, DePhilippo said.

Other records indicate the colonel’s burial spot is unknown.

DePhilippo has recently been in touch with someone who may have the definitive original documents that could solve the mystery once and for all – or prolong it.

“We won’t know until I hear back,” said DePhilippo.

The cemetery gathering coincided with the annual Cushing family reunion. Since the 1970s the family has met on family land on Long Island every year on the third Sunday in July. About 100 near and far-flung Cushing descendants eat, play games like egg toss and treasure hunt, and talk family lore, said Gary Cushing of Chelmsford, Massachusetts, who carried a family genealogy to Saturday’s scanning.

All eyes focused on Vaillancourt and his scanner.

Vaillancourt said he donates his time and skills about half a dozen times a year to families like the Cushings who are researching burial sites.

“I am a history buff,” said Vaillancourt, a Scarborough resident.

Vaillancourt ran his scanning equipment, which looks something like a snowblower, over the unmarked plot the family assumes could be the colonel’s resting place.

“What is typically left of a 250-year-old grave?” Melwani wondered aloud.

Vaillancourt said his equipment detected an oblong disturbance about 3½ to 4 feet deep, consistent with burial practices of the time.

“I am 75 to 85 percent sure there is something here that is the right depth and the right width to be a grave,” Vaillancourt announced.

While it was not the definitive evidence needed to officially declare the spot Ezekiel Cushing’s final resting place, it was enough information to send the family happily off to catch the ferry to Long Island.

“I am very satisfied about the results,” said Melwani.