that it lived principally upon fishes;
but its powerful wings at the same time indicate that it was
capable of prolonged flight. The tail of _Ichthyornis_ has,
unfortunately, not been discovered; and it is at present impossible
to say whether this resembled the tail of existing Birds, or
whether it was elongated and composed of separate vertebrae, as
in the Jurassic _Archoeopteryx_.

Still more wonderful than _Ichthyornis_ is the marvellous bird
described by Marsh under the name of _Hesperornis regalis_. 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. The
known remains of _Hesperornis regalis_ prove it to have been a
swimming and diving bird, of larger dimensions than any of the
aquatic members of the class of Birds with which we are acquainted
at the present day. It appears to have stood between five and six
feet high, and its inability to fly is fully compensated for by the
numerous adaptations of its structure to a watery life. Its teeth
prove it to have been carnivorous in its habits, and it probably
lived upon fishes. It is a curious fact that two Birds agreeing
with one another in the wholly abnormal character of possessing
teeth, and in other