an fifty feet, the neck consisting of over sixty
vertebrae and measuring over twenty feet in length. The extraordinary
Flying Reptiles of the Jurassic are likewise well represented in
the Cretaceous rocks by species of the genus _Pterodactylus_
itself, and these later forms are much more gigantic in their
dimensions than their predecessors. Thus some of the Cretaceous
Pterosaurs seem to have had a spread of wing of from twenty to
twenty-five feet, more than realising the "Dragons" of fable in
point of size. The most remarkable, however, of the Cretaceous
_Pterosaurs_ are the forms which have recently been described
by Professor Marsh under the generic title of _Pteranodon_. In
these singular forms--so far only known as American--the animal
possessed a skeleton in all respects similar to that of the typical
Pterodactyles, except that the jaws are completely destitute of
teeth. There is, therefore, the strongest probability that the
jaws were encased in a horny sheath, thus coming to resemble the
beak of a Bird. Some of the recognised species of _Pteranodon_
are very small; but the skull of one species (_P. Longiceps_)
is not less than a yard in length, and there are portions of
the skull of another species which would indicate a length of
four feet for the cranium. These measurements would point to
dimensions larger than those of any other known Pterosaurs.

The great Mesozoic order of the _Deinosaurs_ is largely represented
in the Cretaceous rocks, partly by genera which previously existed
in the Jurassic period, and partly by entirely new types. The great
delta-deposit of the Wealden, in the Old World, has yielded the
remains of various of these huge terrestrial Reptiles, and very
many others have been found in the Cretaceous deposits of North
America. One of the most celebrated of the Cretaceous Deinosaurs
is the _Iguanodon_, so called from the curious resemblance of
its teeth to those of the existing but comparatively diminutive
_Iguana_. The teeth (fig. 209) are soldered to the inner face
of the jaw, instead of being sunk in distinct sockets; and they
have the form of somewhat flattened prisms, longitudinally ridged
on the outer surface, with an obtusely triangular crown, and
having the enamel crenated on one or both sides. They present
the extraordinary feature that the crowns became worn down flat
by mastication, showing that the _Iguanodon_ employed its teeth
in actually chewing and triturating the vegetable ma