Argo Navis (the Ship Argo), or simply Argo, was a large constellation in the southern sky that has since been divided into three constellations. It represented the Argo, the ship used by Jason and the Argonauts in Greek mythology. The genitive was "Argus Navis", abbreviated "Arg".  Flamsteed and other early modern astronomers called the constellation just Navis (the Ship), genitive "Navis", abbreviated "Nav".