The incident, on Long Nook Beach in Truro, occurred Wednesday afternoon, Aug. 15.
The man, identified as William Lytton of Scarsdale according to the Boston Herald, was flown to a Boston hospital by medical helicopter.
He is listed in serious condition at Tufts Medical Center in Boston, according to the Herald.
The breed of shark that attacked Lytton has not yet been determined. It was Massachusetts' first shark attack in six years.
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