The real construction of the Iguanodon was gradually built up by later discoveries, and in 1877 an extraordinary find in a coal mine at Bernissart in Belgium brought to light no less than seventeen skeletons more or less complete. These were found in an ancient fissure filled with rocks of Comanchic age, traversing the Carboniferous strata in which the coal seam lay, and with them were skeletons of other extinct reptiles of smaller size. The open fissure had evidently served as a trap into which these ancient giants had fallen, and either killed by the fall or unable to escape from the pit, their remains had been subsequently covered up by sediments and the pit filled in to remain sealed up until the present day. These skeletons, unique in their occurrence and manner of discovery, are the pride of the Brussels Museum of Natural History, and, together with the earlier discoveries, have made the _Iguanodon_ the most familiar type of dinosaur to the people of England and Western Europe. [Illustration: Fig. 27.--Teeth of the duck-billed dinosaur _Trachodon_. The dental magazine has been removed from the lower jaw and is seen to consist of several close-set rows of numerous small pencil-like teeth which are pushed up from beneath as they wear off at the grinding surface.] _Camptosaurus._ The American counterpart of the Iguanodons of Europe was the _Camptosaurus_, nearly related and generally similar in proportions but including mostly smaller species, and lacking some of the peculiar features of the Old World genus. In the National Museum at Washington, are mounted two skeletons of _Camptosaurus_, a large and a small species, and in the American Museum a skeleton of a small species. It suggests a large kangaroo in size and proportions, but the three-toed feet, with hoof-like claws, the reptilian skull, loosely put together, with lizard-like cheek teeth and turtle beak indicate a near relative of the great _Iguanodon_. _Thescelosaurus._ The Iguanodont family survived until the close of the Age of Reptiles, with no great change in proportions or characters. Its latest member is _Thescelosaurus_, a contemporary of _Triceratops_. Partial skeletons of this animal are shown in the Dinosaur Hall; a more complete one is in the National Museum. FOOTNOTES: [Footnote 15: Trachodont teeth never drop out, they are completely consumed. Only in the Iguanodonts and Ceratopsia are they shed.--B. Brown.] CHAPTER VII. THE BEAKED DINOSAURS (Continued). B. THE DUCK BILLED DINOSAURS,--TRACHODON, SAUROLOPHUS, ETC. _Sub-Order Ornithopoda; Family Trachodontidae._