This aroused the interest of Doctor Spencer F. Baird of the Smithsonian Institution, who sent T. A. Culbertson to the Bad Lands to make further collections. The latter was successful in securing a valuable series of mammalian and chelonian remains. These, together with other specimens from the same locality, were sent to Leidy, for, as Baird remarked, Leidy, although only thirty years of age, was the only anatomist in the United States qualified to determine their nature. The outcome of Leidy’s study of this material was “The Ancient Fauna of Nebraska,” published in 1853, and constituting the most brilliant work which up to that time American paleontology had produced. Leidy’s determinations, which are in the main correct, are the more remarkable when it is realized that he had little recent osteological material for comparative study. The forms thus described by him were new to science, of a more generalized character than those now living, and yet their distinguished describer recognized, either at that time or a little later, their true relationship to the modern types. The extent of Leidy’s anatomical knowledge was almost Cuvierian, and Cuvier-like he established the fact of the presence of the rhinoceroses, then unheard of in the American fauna, from a few small fragments of molar teeth, an opinion shortly to be fully sustained through the finding of complete molars and the entire skull of the _same individual animal_. Leidy next turned his attention to the huge edentates, which he studied exhaustively, publishing his results in the form of a memoir in 1855, two years after the appearance of the “Ancient Fauna.” Extinct fishes of the Devonian of Illinois and Missouri and the Devonian and Carboniferous of Pennsylvania were made the subjects of his next researches, after which he described the peccaries of Ohio, and later, in a much larger and most important work, the Cretaceous reptiles of the United States (1865). Most of the fossils discussed in this last work are from the New Jersey Cretaceous marls and of them the most notable was the herbivorous dinosaur _Hadrosaurus_, the structure and habits of which, together with its affinities with the Old World iguanodons, Leidy described in detail. From Leidy’s descriptions and with his aid, Waterhouse Hawkins was enabled to restore a replica of the skeleton in a remarkably efficient way. This restoration for a long time graced the museum of the Philadelphia Academy of Natural Sciences and there was a plaster replica of it in the United States National Museum. These, together with plaster replicas of _Iguanodon_ from the Royal College of Surgeons in London, gave to Americans their first real conceptions of members of this most remarkable group. The associated fossils from the New Jersey marls were chiefly crocodiles and turtles.