"Better come in," he said to the master of the Swallow.
"Not to-day, lad," came back the answer. "How is the bottom where you are swimming?"
"Sandy, with a few shells," answered Dave. "Do you know what I am thinking?" he went on. "There may be pearls here."
"Perhaps."
"I'm going to do some diving and take a look around."
Dave was as good as his word and dove not once but a dozen times. He brought up a peck of oysters, but none containing pearls.
"Must have been mistaken," he said. "I'll try it once again."
He made a beautiful dive and reached the bottom with ease.
But scarcely had he put out his hand for an oyster when he saw something that filled him with alarm.
A long, dark object was moving along the ocean bottom towards him.