Like other reptiles, living and extinct, Thespesius was continually renewing his teeth, so that as fast as one tooth was worn out it was replaced by another, a point wherein Thespesius had a decided advantage over ourselves. On the other hand, as there was a reserve supply of something like 400 teeth in the lower jaw alone, what an opportunity for the toothache! And then we have a multitude of lesser Dinosaurs, including the active, predatory species with sharp claws and double-edged teeth. Megalosaurus, the first of the Dinosaurs to be really known, was one of these carnivorous species, and from our West comes a near relative, Ceratosaurus, the nose-horned lizard, a queer beast with tiny fore legs, powerful, sharp-clawed hind feet, and well-armed jaws. A most formidable foe he seems, the more that the hollow bones speak of active movements, and Professor Cope pictured him, or a near relative, vigorously engaged in combat with his fellows, or preying upon the huge but helpless herbivores of the marshes, leaping, biting, and tearing his enemy to pieces with tooth and claw. Professor Osborn, on the other hand, is inclined to consider him as a reptilian hyena, feeding upon carrion, although one can but feel that such an armament is not entirely in the interests of peace. Last, but by no means least, are the Stegosaurs, or plated lizards, for not only were they beasts of goodly size, but they were among the most singular of all known animals, singular even for Dinosaurs. They had diminutive heads, small fore legs, long tails armed on either side near the tip, with two pairs of large spines, while from these spines to the neck ran series of large, but thin, and sharp-edged plates standing on edge, so that their backs looked like the bottom of a boat provided with a number of little centreboards. Just how these plates were arranged is not decided beyond a peradventure, but while originally figured as having them in a single series down the back it seems much more probable that they formed parallel rows. [Illustration: Fig. 23.--The Horned Ceratosaurus. A Carnivorous Dinosaur. _From a drawing by J. M. Gleeson._] The largest of these plates were two feet in height and length, and not more than an inch thick, except at the base, where they were enlarged and roughened to give a firm hold to the thick skin in which they were imbedded. Be it remembered, too, that these plates and spines were doubtless covered with horn, so that they were even longer in life than as we now see them. The tail spines varied in length, according to the species, from eight or nine inches to nearly three feet, and some of them have a diameter of six inches at the base. They were swung by a tail eight to ten feet long, and as a visitor was heard to remark, one wouldn't like to be about such an animal in fly time.