The great White Shark, the man-eater, so often found in story books, so rarely met with in real life, attains a length of thirty feet, and a man just makes him a good, satisfactory lunch. Now a tooth of this shark is an inch and a quarter long, while a tooth of the huge _Megalodon_ is commonly three, often four, and not infrequently five inches long. Applying the rule of three to such a tooth as this would give a shark 120 feet long, bigger than most whales, to whom a man would be but a mouthful, just enough to whet his sharkship's appetite. Even granting that the rule of three unduly magnifies the dimensions of the brute, and making an ample reduction, there would still remain a fish between seventy-five and one hundred feet long, quite large enough to satisfy the most ambitious of _tuna_ fishers, and to have made bathing in the Miocene ocean unpopular. Contemporary with the great-toothed shark was another and closely related species that originated with him in Eocene times, and these two may possibly have had something to do with the extinction of Zeuglodon. This species is distinguished by having on either side of the base of the great triangular cutting teeth a little projection or cusp, like the "ear" on a jar, so that this species has been named _auriculatus_, or eared. The edges of the teeth are also more saw-like than in those of its greater relative, and as the species must have attained a length of fifty or sixty feet it may, with its better armature, have been quite as formidable. And, as perhaps the readers of these pages may know, the supply of teeth never ran short. Back of each tooth, one behind another arranged in serried ranks, lay a reserve of six or seven smaller, but growing teeth, and whenever a tooth of the front row was lost, the tooth immediately behind it took its place, and like a well-trained soldier kept the front line unbroken. Thus the teeth of sharks are continually developing at the back, and all the teeth are steadily pushing forward, a very simple mechanical arrangement causing the teeth to lie flat until they reach the front of the jaw and come into use.