Mart and Dailey glanced around, and an echoing cry broke from the seaman. Fifty yards ahead of them and slowly cutting the water in their direction, was a black triangle that seemed part of some machine, so evenly and steadily did it move along. But the size of it! Mart guessed instantly that it was the dorsal fin of a shark, but he had seen no fin of such size before.
"It's the Pirate Shark, Holly!" he cried suddenly, and plunged down for the rifle. Bob stooped for it at the same instant, but Mart was too quick for him. He rose again to find Dailey looking at them, aghast.
"Where might you lads 'a' heard o' the Pirate Shark?" queried the seaman hoarsely. Mart had no time to waste on him.
"None of your business," he returned sharply. "Keep steady there—"
"You'll waste the bullet, Mart," and Bob stopped him. "It'll simply glance off the water at this angle. Hold on till we get closer!"
"Don't you do it, sir," implored Dailey, his leathery face suddenly pale. "It's the Pirate Shark, all right—don't you fire on him, sir! My word on it, Mr. Judson, it'll be a bad day for us all—"
"Oh, cut out that superstitious talk, Dailey," broke in Mart impatiently. "He's a shark, and a big one; pirate or not, if I can't get to him I'll put a bullet through that big fin of his."
"That's the idea!" exclaimed Bob. "But quit talking or we'll scare him off. Hit the fin, Mart—don't waste time tryin' to make the bullet penetrate the water unless we get up close alongside."
Mart, quivering with excitement, got a bead on that tremendous black fin which was now turning as if to proceed across their bows. It would be futile to attempt shooting the shark at such a distance, for as Bob said the bullet would simply glance from the surface of the water.
Suddenly Mart perceived that the fin was turning away from them. Instantly he sighted for its center, made sure of his bead, and fired. He saw the fin flutter wildly, then there was a great swirl of waters, and as the heavy detonation rang over the lagoon the black fin vanished amid the foam.