By Joseph Ax

(Reuters) - Former mob boss James "Whitey" Bulger's personal possessions - including a pen holder designed to look like a rat and a three-carat, heart-shaped diamond ring - fetched more than $100,000 at an auction in Boston on Saturday.

Law enforcement officials sold off hundreds of items seized when federal agents captured the fugitive mobster in an apartment in Santa Monica, California, in 2011.

Bulger, 86, ruled Boston's criminal underworld for a quarter-century before going on the lam after a corrupt FBI agent alerted him that he was about to be arrested. He survived 16 years on the run before he was finally caught with $800,000 in cash and a cache of weapons.

The items sold on Saturday ranged from the mundane to the unique. Three pairs of sneakers, along with a pair of black slippers and a pair of sandals, went for $210; a punching bag shaped like a man drew $4,900; and an enormous collection of books, many of them focused on World War II and the Holocaust and containing Bulger's handwritten notes, sold for thousands of dollars in all.

The white bucket hat Bulger was wearing at the time of his capture went for $6,400.

The auction ended around 2 p.m., with the final sale a floor safe for $525.

The proceeds of the auction will go to his victims, according to the U.S Marshals Service, which is overseeing the auction.

Bulger was convicted in 2013 of either committing or ordering 11 murders, among other crimes, and sentenced to two consecutive life sentences. He is in federal prison in Sumter, Florida.

His longtime girlfriend, Catherine Greig, who lived in hiding with Bulger and who owned a number of the items up for auction on Saturday, was sentenced to eight years for harboring a fugitive. In April, she received an additional 21 months after refusing to answer questions as to whether anyone helped the couple while in hiding.

Bulger's rise to power and eventual flight were chronicled in the book "Black Mass," which was adapted into a 2015 film starring Johnny Depp as the mobster.

(Reporting by Joseph Ax; Additional reporting by Scott Malone; Editing by David Gregorio)