d of the tail, and the head
probably stood eighteen feet from the ground. One of the last great
representatives of the group in America, the Trachodon, about thirty
feet in length, had a most extraordinary head. It was about three and
a half feet in length, and had no less than 2000 teeth lining the mouth
cavity. It is conjectured that it fed on vegetation containing a large
proportion of silica.

In the course of the Jurassic, as we saw, a branch of these biped,
bird-footed vegetarians developed heavy armour, and returned to the
quadrupedal habit. We find them both in Europe and America, and must
suppose that the highway across the North Atlantic still existed.

The Stegosaur is one of the most singular and most familiar
representatives of the group in the Jurassic. It ran to a length of
thirty feet, and had a row of bony plates, from two to three feet in
height, standing up vertically along the ridge of its back, while its
tail was armed with formidable spikes. The Scleidosaur, an earlier
and smaller (twelve-foot) specimen, also had spines and bony plates to
protect it. The Polacanthus and Ankylosaur developed a most effective
armour-plating over the rear. As we regard their powerful armour, we
seem to see the fierce-toothed Theropods springing from the rear upon
the poor-mouthed vegetarians. The carnivores selected the vegetarians,
and fitted them to survive. Before the end of the Mesozoic, in fact, the
Ornithopods became aggressive as well as armoured. The Triceratops had
not only an enormous skull with a great ridged collar round the neck,
but a sharp beak, a stout horn on the nose, and two large and sharp
horns on the top of the head. We will see something later of the
development of horns. The skulls of members of the Ceratops family
sometimes measured eight feet from the snout to the ridge of the collar.
They were, however, sluggish and stupid monsters, with smaller brains
even than the Sauropods.

Such, in broad outline, was the singular and powerful family of the
Mesozoic Deinosaurs. Further geological research in all parts of the
world will, no doubt, increase our knowledge of them, until we can fully
understand them as a great family throwing out special branches to meet
the different conditions of the crowded Jurassic age. Even now they
afford a most interesting page in the story of evolution, and their
total disappearance from the face of the earth in the next geological
period will not be unintelligibl