A porcupine fish helmet.
"Porcupine fish helmet from Kiribati, Oceania. Part of the Pitt Rivers Museum Founding Collection. Given to the Museum in 1884. This helmet is made from an entire porcupine fish, also known as a blowfish. It comes from Kiribati (pronounced 'kiri-bass'), a group of islands in the Micronesia in the Pacific. Before the 1970s they were a British colony and were known as the Gilbert and Ellice Islands. The Pitt Rivers Museum holds one of the most extensive collections of Kiribati arms and armour in the world."