Argo Navis ("the ship Argo") is a defunct constellation in the southern sky which depicted the 50-oared galley Argo used by Jason and the Argonauts in their quest for the Golden Fleece in the famous Greek myth.
Argo Navis was a gigantic constellation, by far the largest constellation of them all, in fact, and was considered so unwieldy that in 1752, when the French astronomer Nicolas Louis de Lacaille subdivided it into Carina (the keel), Puppis (the poop deck), and Vela (the sails), his grateful peers were only too happy to take his idea and run with it, unceremoniously consigning Argo Navis, unlamented, into the dustbin of history, and the astronomy world has never looked back.
Argo Navis remains the only one of the 48 constellations recognized by the ancient Greeks and recorded by 2nd century astronomer Ptolemy of Alexandria in the Almagest that is no longer recognized by modern astronomers. Carina, Puppis, and Vela remain recognized to this day, however. The modern constellation Pyxis (the mariner's compass) was originally viewed as the mast of the Argo by the ancients, but is not recognized as such anymore.
Amazingly, as big as Argo Navis already was, it actually represented only the rear portion of the ship Argo. Thus in old star charts the ship is drawn either sailing into a bank of fog or beginning to sail between the Clashing Rocks, in order to explain why only half a ship is shown.