Or, again, notice the specimens of the genus Cidastes, which are also described as veritable sea-serpents of those ancient seas, whose huge bones and almost incredible number of vertebræ show them to have attained a length of nearly two hundred feet. The remains of no less than ten of these monsters were seen by Professor Mudge, while riding through the Mauvaise Terres of Colorado, strewn upon the plains, their whitened bones bleached in the suns of centuries, and their gaping jaws armed with ferocious teeth, telling a wonderful tale of their power when alive. The same deposits have been equally fertile in the remains of terrestrial animals of gigantic size. The _Titanosaurus montanus_, believed to have been herbivorous, is estimated to have reached fifty or sixty feet in length; while other Dinosaurians of still more gigantic proportions, from the Jurassic beds of the Rocky Mountains, have been described by Professor Marsh. Among the discovered remains of _Atlantosaurus immanis_ is a femur over six feet in length, and it is estimated from a comparison of this specimen with the same bone in living reptiles that this species, if similar in proportions to the crocodile, would have been over one hundred feet in length. But even yet the limit has not been reached, and we hear of the discovery of the remains of another form, of such Titanic proportions as to possess a thigh-bone over twelve feet in length. [Illustration: FIG. 5.--MONSTER BONES OF EXTINCT GIGANTIC SAURIANS FROM COLORADO, SHOWING RELATIVE PROPORTIONS TO CORRESPONDING BONE IN THE CROCODILE (A). (_From the "Scientific American."_)] From these considerations it is evident that, on account of the dimensions usually assigned to them, no discredit can be attached to the existence of the fabulous monsters of which we shall speak hereafter; for these, in the various myths, rarely or never equal in size creatures which science shows to have existed in a comparatively recent geological age, while the quaintest conception could hardly equal the reality of yet another of the American Dinosaurs, _Stegosaurus_, which appears to have been herbivorous, and more or less aquatic in habit, adapted for sitting upon its hinder extremities, and protected by bony plate and numerous spines. It reached thirty feet in length. Professor Marsh considers that this, when alive, must have presented the strangest appearance of all the Dinosaurs yet discovered. The affinities of birds and reptiles have been so clearly demonstrated of late years, as to cause Professor Huxley and many other comparative anatomists to bridge over the wide gap which was formerly considered to divide the two classes, and to bracket them together in one class, to which the name Sauropsidæ has been given.[35]