Peter Matthiessen, a roving author and naturalist whose impassioned nonfiction explored the remote endangered wilds of the world and whose prize-winning fiction often placed his mysterious protagonists in the heart of them, died on Saturday at his home in Sagaponack, N.Y. He was 86... Mr. Matthiessen was one of the last survivors of a generation of American writers who came of age after World War II and who all seemed to know one another, socializing in New York and on Long Island’s East End as a kind of movable literary salon peopled by the likes of William Styron, James Jones,...