impossible to say whether they differed from existing birds in any
essential character or not. In your country the development of the
cretaceous series of rocks is enormous; the conditions under which the
later cretaceous strata have been deposited are highly favourable to the
preservation of organic remains; and the researches, full of labour and
risk, which have been carried on by Professor Marsh in these cretaceous
rocks of Western America, have rewarded him with the discovery of forms
of birds of which we had hitherto no conception. By his kindness, I am
enabled to place before you a restoration of one of these extraordinary
birds, every part of which can be thoroughly justified by the more or
less complete skeletons, in a very perfect state of preservation, which
he has discovered. This _Hesperornis_ (Fig. 3), which measured between
five and six feet in length, is astonishingly like our existing divers
or grebes in a great many respects; so like them indeed that, had the
skeleton of _Hesperornis_ been found in a museum without its skull, it
probably would have been placed in the same group of birds as the divers
and grebes of the present day.[1]

[Illustration: FIG. 3.--HESPERORNIS REGALIS (Marsh).]

But _Hesperornis_ differs from all existing birds, and so far resembles
reptiles, in one important particular--it is provided with teeth. The
long jaws are armed with teeth which have curved crowns and thick roots
(Fig. 4), and are not set in distinct sockets, but are lodged in a
groove. In possessing true teeth, the _Hesperornis_ differs from every
existing bird, and from every bird yet discovered in the tertiary
formations, the tooth-like serrations of the jaws in the _Odontopteryx_
of the London clay being mere processes of the bony substance of the
jaws, and not teeth in the proper sense of the word. In view of the
characteristics of this bird we are therefore obliged to modify the