In Plate V. we have endeavoured to give some idea of a huge thigh-bone (femur) belonging to the truly gigantic Dinosaur called Atlantosaurus. It is six feet two inches long, and a cast of it may be seen in the fossil reptile gallery of the British Museum of Natural History (Wall-case No. 3). It should be mentioned, however, that the original specimen is partly restored, so that its exact length to an inch or so is not quite certain. In our illustration it is shown to be a little taller, when placed upright, than a full-grown man. Professor Marsh, the fortunate discoverer of this wonderful bone, calculates that the Atlantosaurus must have attained a length of over eighty feet! and, assuming that it walked upon its hind feet, a height of thirty feet! It doubtless fed upon the luxuriant foliage of the sub-tropical forests, portions of which are preserved with its remains. Besides this thigh-bone, Professor Marsh has procured specimens of vertebræ from the different parts of the vertebral column; but no skull or teeth. The vertebræ are hollowed out much in the same way as those of Brontosaurus. The fore limbs were large, as in the latter animal; and the extremities of the limbs were provided with claws. Taking all present evidence, it appears that the Atlantosaurus bore a general resemblance to its smaller contemporary. We can therefore form a fairly good idea of its aspect and proportions. The same Jurassic strata from the Rocky Mountains have yielded remains of another big Dinosaur, belonging to the same family. This genus, which has been named the Apatosaurus, is represented by a nearly complete skeleton, in the Yale College Museum; and is fortunately in an excellent state of preservation. Another species, of smaller size, though not so complete, adorns the same collection. This was about thirty feet long, and is known as Apatosaurus grandis. [Illustration: Plate V. THIGH-BONE OF THE LARGEST OF THE DINOSAURS, ATLANTOSAURUS. From a cast in the Natural History Museum. Length 6 feet 2 inches.] Morosaurus, another important genus, is known from a large number of individuals discovered in the now famous Atlantosaurus beds of Colorado, including one nearly complete skeleton. The head of this creature was small; the neck elongated; and the vertebræ of the neck are lightened by deep cavities in their centra, similar to those in birds of flight. The tail, also, was long. When alive, this Dinosaur was about forty feet in length. It probably walked on all fours; and in many other respects was very unlike a typical Dinosaur. The brain was small, and it must have been sluggish in all its movements. The nearly complete remains of Morosaurus grandis were found together in a very good state of preservation in Wyoming, and many of the bones lay just in their natural positions.