filled me with alarm.

Presently a door in one side of the arena wall was opened to admit
a huge, shaggy, bull-like creature.

"A Bos," whispered Perry, excitedly. "His kind roamed the outer
crust with the cave bear and the mammoth ages and ages ago. We
have been carried back a million years, David, to the childhood of
a planet--is it not wondrous?"

But I saw only the raven hair of a half-naked girl, and my heart
stood still in dumb misery at the sight of her, nor had I any eyes
for the wonders of natural history. But for Perry and Ghak I should
have leaped to the floor of the arena and shared whatever fate lay
in store for this priceless treasure of the Stone Age.

With the advent of the Bos--they call the thing a thag within
Pellucidar--two spears were tossed into the arena at the feet of
the prisoners. It seemed to me that a bean shooter would have been
as effective against the mighty monster as these pitiful weapons.

As the animal approached the two, bellowing and pawing the ground
with the strength of many earthly bulls, another door directly
beneath us was opened, and from it issued the most terrific roar
that ever had fallen upon my outraged ears. I could not at first
see the beast from which emanated this fearsome challenge, but
the sound had the effect of bringing the two victims around with
a sudden start, and then I saw the girl's face--she was not Dian!
I could have wept for relief.