​LOUISIADE (lö-ē-zē-äd′) ARCHIPELAGO, a group of islands belonging to British New Guinea, and forming an E. extension of that island; it embraces Sudest (45 miles long by 4 to 10 miles wide), Rossel, St. Aignan's (28 miles long by 8 to 9 miles wide), and a vast number of smaller islands. All are mountainous, rising to 3,500 in St. Aignan's and covered with vegetation. The natives seem to partake of both Malayan and Papuan characteristics.