Abstract — Protosiren eothene is a new species of early Lutetian (early middle Eocene) sirenian collected from sediments deposited in a coastal marine setting in eastern Tethys. It was found in the upper part of the Habib Rahi Formation in the vicinity of Kunvit, near Rakhni, in eastern Balochistan Province, Pakistan. The new sirenian is represented by distinctive thoracic vertebrae and ribs of a mature adult. Features of Protosiren that are generally diagnostic include the presence of large keyhole-shaped neural canals perforating thoracic vertebrae, presence of cartilaginous rather than synovial articulations of rib heads, and a lack of rib pachyostosis. Protosiren eothene is the oldest and smallest species of Protosiren known to date. It retains synovial articulations on rib heads, and it is about 10-12% smaller in linear dimensions than P. fraasi from the early middle Eocene of Egypt.