Hastening to the spot indicated the boys saw what looked to be a horse’s foot upside down in the sand.  So startling was the resemblance that Jack and Arnold were completely deceived for a moment, but Frank’s laugh soon indicated that they had been mistaken.

“What is it?” asked Arnold eagerly.  “Gee, but I see so many new things here I don’t know which to write a story about first.”

“Better not write any story about this,” admonished Frank.  “The wonderful phenomenon you see before you, my friend, is not a horse at all.  It is merely a crab shell from which the crab has gone.”

“A crab shell?” repeated Arnold in wonderment.  “A real crab?”

“Sure enough,” declared Frank.  “The underside of the shell has exactly the same outlines as the under side of a horse’s foot.  This fellow has projecting from the heel a spikey tail that is hard and sharp at the end.  The whole thing, as you see, is dried and hardened by exposure to the weather.  The crab has been gone a long time.”

“I’m going to take it along,” asserted Arnold.  “I’ll put it in my locker and make a collection of things I pick up.  I’d like to see a flounder now so as to recognize one the next time I see it.”

“I have a fine big fellow at the place I had my fires,” Frank answered.  “We’ll go over there and see how he’s getting on.  I got him last night.  I think he must weigh as much as three or four pounds.”

“Tell me some more about this Spanish Treasure Chest,” Jack said as the boys turned toward the site of Frank’s camp.  “I’m anxious to know everything you overheard anywhere that would have a bearing on the matter from any viewpoint.  It’s interesting.”

“I can’t tell you any more than I have.  I know these fellows objected to our visiting this locality because they seemed to believe that we were trying to get something that belonged to them and they were ready to employ force if necessary to keep us out,” Frank said.

“We know they are a desperate gang,” Jack admitted.  “Our own experiences show that.  They also believe we are here on the same mission and already they have attempted to disable and sink our boat.”

Frank stopped in alarm.  Glancing hurriedly about he grasped Jack’s arm and in a trembling tone entreated him to leave the vicinity at his earliest opportunity.  Jack’s answer was a negative shake of his head.  His companions also indicated their disapproval of the course.

“Well, here’s the flounder,” announced Frank at last picking up a fine specimen of that denizen of the Gulf waters.  “He’s a beauty.”

The boys gathered about the fish admiring and investigating the peculiarities already mentioned by Frank.  At last Harry spoke: 

“But he wouldn’t be good raw and you had to have a fire.  I’m always interested in seeing fire produced from a stick.”

“Oh, that’s not so difficult,” Frank answered; “watch me.”

Kneeling on the sand he grasped his fire stick in his left hand after placing the bowstring in position.  With a shell over the upper end of the stick, he sawed away busily for a moment.  A tiny wreath of smoke eddied away from the lower end of the stick.