Horrid Massacre. A horrid massacre and mutiny occurred at New Zealand on board the ship Ploughboy, of Nantucket on June 18th last, as we learn by the Nantucket Enquirer. Three natives having been hired to complete the crew, for some supposed injury murdered in the night an American sailor named John Coles, of Nantucket, and a Dane, and wounded a third. One of the men killed was beheaded. The steersman, stabbed with a spear, and falling dead through the light, aroused those below, who on reaching the deck, found the natives had cut adrift all the boats and were making off. One of them, however, was shot and killed. The boats were recovered next morning.