“A horned viper!” exclaimed Bob fearfully, recognizing the long, sinister body that was coiled almost at their feet.

“And it’s going to strike!” cried Joe. “Get your pistol—quick! We’ll both fire at it. Oh, how I wish we had our rifles!”

The snake was preparing to lunge forward, its terrible head swaying slowly from side to side. Whether or not the fangs contained poison, the boys did not know, but they knew they could not take a chance.

Neither Bob nor Joe was an outstanding shot with a revolver, and they felt rather panic-stricken as they raised the weapons and took aim.

After a few seconds that seemed to the youths like hours, Bob pulled the trigger.

A moment later the cold sweat burst out on his forehead, as he saw that he had missed. Before he could take another aim, the reptile would be upon him, a mass of scaly ferocity.

Bang!

Joe’s pistol spoke out, and the bullet caught the snake in the neck, just as it was about to strike.

Another shot from Joe’s automatic struck in a vital spot. The fiendish head turned violently, then fell to the ground with a thud. The tail twitched about momentarily, and as life passed out, the horrible body lay still.

It was some time before Bob and Joe could regain their natural peace of mind, for the strain had been great. Their hearts were beating rapidly from the unusual mental exertion.

“A narrow escape!” breathed Joe, putting his gun back in its holster.

“Thanks to you, old boy, we came out alive,” praised Bob, giving his friend an affectionate pat on the back. “It was your coolness and determination that sent those bullets in the right place. I was too nervous, I guess.”

“But say,” began Joe, turning aside the commendation of his friend, “our dads might want this fellow as a specimen. Do you suppose they would? Those bullets didn’t shatter it as a rifle cartridge would have.”

The youths were not particularly anxious to handle the long, scaly body, but they felt it their duty to do all they could for their fathers.

“What say we take it to the edge of the hill and roll it down?” suggested Bob. “The way is gradual and there are no protruding crags to tear it.”

“All right. We never can carry it without falling ourselves.”

The reptile was pushed over the side of the dune, and the boys made their way down. They slid more than climbed, but reached the bottom uninjured.

Mr. Lewis came out to meet them, on his face a look of anxiety.

“What kept you so long?” he asked.

“That over there,” replied Joe, pointing to the snake, which lay but a few feet away.

The naturalist ran over to it. Then he straightened up in surprise.

“A horned viper,” he pronounced. “Where’d you find it?”

Bob related the narrow escape at the top of the dune, not forgetting to point out Joe’s part in killing the reptile. When he had finished, Mr. Lewis shook his head gravely.

“Never leave camp without your rifles,” he warned them. “In a strange land anything is likely to happen.”

During breakfast the youths’ experience with the viper was the chief topic for conversation. Tishmak looked at the boys with a new respect as he heard the account of their daring deed.

As soon as the morning meal was over, the tent and provisions were packed back on the dromedaries, and the explorers continued their journey.

“How much ground did we probably cover yesterday?” asked Dr. Kirshner of Fekmah, as they followed a narrow way between the rolling sand dunes.

“At least a hundred miles,” the Arab answered. “Perhaps many more. Dromedaries trot rather rapid.”

“Then, at that rate, it shouldn’t take us so very long to reach the Ahaggaras, should it?” asked Joe, who with Bob had not yet taken his place at the end of the caravan.

“No. But something could keep us back. Maybe storm, or could be bandits. Never know about that.”

As the explorers moved on, they occasionally saw small animals and birds. The naturalists were constantly on the lookout, shooting any creature that came within range of their guns. Among the victims of their marksmanship were desert larks, rats, hares, lizards, and a small animal called the ferrec.

Bob and Joe kept their time occupied in taking motion pictures of the country they were passing through. By the time that their caravan had stopped for the midday meal, the boys had “rolled off” a good many hundred feet of film.

“Here’s hoping our moving pictures here prove to be as successful as those that we took in Brazil,” said Joe, as he took out a bag of rations from a camel’s pack.

“If they do, the Neuman Film Corporation may give us a job on every future expedition we might make with our dads,” came from Bob.

Thus far the day’s traveling had not yet brought them to an oasis. Tishmak informed them that water would probably not be found until late the next night. The containers, however, held a large supply, making it unnecessary for the explorers to worry.

“It’s a good thing the dromedaries don’t need it often,” said Mr. Lewis, as he went about preparing the meal.

“Four or five days is often enough for them,” put in Mr. Holton. “They can go much longer than that, but it isn’t wise to risk it.”

It was about eleven o’clock, the time advisable to begin the usual afternoon rest. Bob and Joe were glad of the chance to escape the heat of the fierce sun. Even in the morning it was too hot for comfort, although nothing compared to the baking atmosphere of the afternoon. The youths were tanned so dark as to resemble Arabs.

“Funny,” smiled Joe. “Back in the United States we fellows wanted to get burned by the sun. Here we try to keep out from under it.”

“All goes to prove that circumstances alter cases,” laughed Dr. Kirshner.

The tent was again pitched, and the meal eaten. This time, however, water was used sparingly. The adventurers did not wish to run the risk of getting dangerously short.

It was thought best to set a guard again while the others slept or idly rested on the cool sand. Mr. Holton took the job, sitting in the shade of the tent facing the resting dromedaries.

“Chances are nothing will turn up, though,” he said, and proved to be right.

Sharply at three o’clock Dr. Kirshner was up stretching himself and suggesting that they continue the journey.

“It isn’t the thing to wait too long,” he reminded his friends, “even if we are drowsy. By night we want to have covered another hundred miles or more. I’m especially anxious to reach the mountainous region and see what I can find in the way of records of ancient peoples who might have lived there before the desert became a desert,” he added, laughing.

The others were more than willing to start on. When sleepiness or drowsiness threatened to overpower them at the wrong time, the thought of the two thieves who had stolen Fekmah’s map spurred them on to action.

“I don’t know that it is necessary to set a guard while we take our afternoon rests,” remarked Fekmah casually, as they packed the tent back in its place for the journey.

The Americans looked at him wonderingly.

“The dromedaries will give us warning,” he explained. “They are much uneasy if stranger come near camp. They jump up and make noise.”

“A bit like watchdogs, are they?” said Mr. Holton. “Well, we’ll give them a tryout the next time.”

They again took up the journey, winding in and out among the rolling sand hills. Occasionally they would come to a dune several hundred feet high. They seemed to be gradually mounting higher, for the camels did not move as rapidly as before.

Vegetation increased still more, giving the dromedaries an opportunity to nibble often on the various plants and shrubs. A few scattered trees began to be seen, their sharp thorns protruding threateningly.

“Camels don’t bother with thorns,” remarked Bob. “They know just where to take a mouthful without cutting their mouths.”

“And they aren’t particular about their diet, either,” Joe added, remembering what Fekmah had told him some time before. “Leather, paper, wood—almost anything will satisfy their appetites.”

At last they came to the region of high sand dunes that were visible the day before. Many of the hills towered five and six hundred feet, and a few were much higher than that. The explorers were lucky in finding a narrow lane that passed between the mounds. How long the good fortune would continue, they did not know.

“Getting to look more like the dunes in Indiana, back in the United States,” remarked Joe. “But of course these stretch a hundred times as far.”

In some places the ground was hard and brittle, while in others it was strewn with loose sand.

At last the lane stopped, and the adventurers found themselves face to face with a high hill.

“Guess we’ll have to climb it,” said Mr. Holton, looking about. “There is no other way out. The sand seems to be hard and safe enough. And it could be a great deal steeper.”

“Let dromedaries go slowly,” cautioned Fekmah. “Do not hurry them.”

They began the dangerous ascent, keeping their eyes glued to the ground. Slowly the camels trudged up, feeling their steps carefully.

They were almost to the top when suddenly the ground gave way from under Joe’s dromedary. The animal fell to its knees, struggled for a moment, and fell backward.

With a wild shout Joe plunged from the animal’s back and went rolling helplessly down the hill!