Argo Navis, or the Argo, the ship sailed by Jason and the Argonauts, is an obsolete constellation. One of Ptolemy's original constellations, its very large size was considered unwieldy, and it was broken up into smaller constellations by Lacaille, in 1752: Carina, the Keel, Puppis, the Poop Deck, and Vela, the Sails. Since this was long after Bayer designated Greek letters for various stars in Argo Navis, each of the three constellations is missing those letters which lie in one of the other constellations.
Lacaille also introduced a fourth constellation, Pyxis, the Mariner's Compass, which lies in a region formerly occupied by part of Argo Navis' mast. However, none of the Bayer stars from Argo Navis lay in Pyxis, so its "Bayer" designations are completely separate from those of the other fragments of Argo Navis.