Hesperornis, a genus of fossil birds, including several species, described by Professor 0. C. Marsh, from the Middle Cretaceous rocks of Western Kansas. They were huge fish-eating Divers, nearly six feet high, with a perfectly flat breast-bone, without a vestige of a keel, and there were apparently not even rudimentary wings. The tail is elongated, somewhat as in Archeeopteryx (q.v.), and the long jaws are armed with numerous teeth in a common groove as in Ichthyosaurus.