Archaeologists unearthed an ancient tomb in the southern Egyptian city of Luxor, known for its treasures dating back to the pharaohs, authorities said Saturday.  Mostafa Waziri, secretary-general of the Supreme Council of Antiquities, said an Egyptian-British mission found the royal tomb in an ancient site on the west bank of the Nile River in Luxor, 650 kilometers (400 miles) south of the capital of Cairo.  He said initial examinations show that the tomb apparently belongs to the 18th Dynasty of Pharaonic Egypt, which spanned from 1550 B.C. to 1292 B.C.