This
presents us with a gigantic diving bird, somewhat resembling the
existing "Loons" (_Colymbus_), but agreeing with _Ichthyornis_
in having the jaws furnished with conical, recurved, pointed
teeth (fig. 212, b). Hence these forms are grouped together in
a new sub-class, under the name of _Odontornithes_ or "Toothed
Birds." The teeth of _Hesperornis_ (fig. 212, d) resemble those
of _Ichthyornis_ in their general form; but instead of being
sunk in distinct sockets, they are simply implanted in a deep
continuous groove in the bony substance of the jaw. The front of
the upper jaw does not carry teeth, and was probably encased in
a horny beak. The breast-bone is entirely destitute of a central
ridge or keel, and the wings are minute and quite rudimentary; so
that _Hesperornis_, unlike _Ichthyornis_, must have been wholly
deprived of the power of flight, in this respect approaching the
existing Penguins. The tail consists of about twelve vertebrae,
of which the last three or four are amalgamated to form a flat
terminal mass, there being at the same time clear indications
that the tail was capable of up and down movement in a vertical
plane, this probably fitting it to serve as a swimming-paddle or
rudder. The legs were powerfully constructed, and the feet were
adapted to assist the bird in rapid motion through the water.
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