the vitiated air. "If I can only settle him, I can cut off these
weights and take a chance on shooting up to the top. It'll be a mighty
slim chance, but it's all I've got."

Rendered desperate by his fear of suffocation, which was even greater
than his fear of the Pirate Shark, he advanced to the edge of the
opening with a resolute determination to take any chance that offered.
Nor was it slow in coming.

Down swept the shark with a rush, flicking in its tail as it passed, and
Mart leaped back only just in time to avoid it. But he saw the brute's
purpose now--to try to suck him out with the swirls of water, or to
strike him over with its tail, and as he eyed the dim gray shape that
was circling around for another rush, he made ready. He must strike as
the huge body flicked past--and he must leap back before the tail could
get to the opening!

That meant only one thing. He would have no chance to pull out his kris
this time. Everything would depend on the one sure stroke, which must be
a death-wound. If not, the kris would be carried off in the shark's
body, and with his little sheath knife alone left him, he would be
helpless.

"Got to do it!" he thought dully, for now his ears were paining, and he
began to feel as if his nose were about to bleed. He was gasping for
air, and forcing up newer air from about his legs and body only relieved
him slightly. "Got to do it this time, or lose out!"

All the water seemed faintly hued with crimson now, and he knew that his
first blow must have worked considerable damage. The shark had dashed
off until he could only see it dimly--a monster shadow that darted
smoothly but erratically about in the distant depths, as if working
itself up to a greater fury. Then it swung about in one wide sweep, and
began to grow plainer as it came down upon him.

Its speed was appalling. During his instant of waiting, Mart's courage
almost failed him; it seemed impossible that he could strike and leap
back in time to avoid the flashing tail!

Nor could he, as it proved. The monster fish drove in upon him, turning
as it came, its bulk seeming to fill all the space above and to crush
him back upon the wreck; then Mart, never giving an inch, shoved his
flame-bladed kris forward, saw it go home to the hilt in the gaping
mouth of the Pirate Shark, and then was swept from his feet.

He went down with a rush in the tremendous swirl of waters, being drawn
along the side of the wreck for a little spac