Grisly trophies from Yale University's mysterious Skull and Bones society, whose members include former president George W. Bush, are to go on auction in New York this month.

The human skull and two large bones are estimated to sell for between 10,000 and 20,000 dollars on January 22 at Christie's.

The auction house said the human remains were used as a ballot box by the secret society. The skull includes a specially cut lid in the top -- apparently for ballots -- and one of the bones is inscribed "THOR."

The auction lot also comes with a black book listing names of Skull and Bones members back in 1831-1877.

"The ballot box and documents offer a rare glimpse into an organization in which membership has evolved into a closely guarded secret," Christie's said.

Members, dubbed "Bonesmen," have included Bush and his father, who also served as president, Senator John Kerry, the late conservative writer William F. Buckley, Jr, and a number of major businessmen such as Averell Harriman and H.J. Heinz II.

The society, joined by leading students at the university and which is said to maintain bizarre initiation rites, was founded at Yale in 1832. Women were admitted for the first time in the 1990s.