86 0. C. Marsh — Omithopoda of 'the American Jurassic. 



The skull, brain, and teeth, of C. medius are shown on Plate 

 IY. The peculiar peg and notch articulation in the sacral 

 vertebra? of this genus, already described, is indicated on Plate 

 YI, figure 2, and a summary of the principal characters of the 

 genus, and of the nearest allied genera, will be found in the 

 text below. 



Dryosaurus, gen. no v. 



Another genus of Jurassic Dinosaurs, allied to Camjrtosau- 

 rus, but differing from it in many important respects, is 

 Dryosaurus, the one here established. The type was described 

 by the writer in 1878, under the name t Laosaurus alius, 

 and a tooth, the pelvis, and a hind leg, were also fig- 

 ured.* Additional material since received shows that this 

 genus is cprite distinct from Laosaurus, to which it was at first 

 referred, and is intermediate between Camptosaurus and that 

 genus, as is shown in a summary of the characters of these 

 genera given later in the present article. 



The European representative of Dryosaurus is Hypsilopho- 

 don, Huxley, from the Wealden of England. That genus, 

 however, differs from the nearest allied forms of this country 

 in several well-marked characters. Among these, the presence 

 of teeth in the premaxillary bones and a well-ossified sternum 

 are features not seen in American Jurassic forms. The fifth 

 digit of the manus, moreover, in Ilypsilophodon is almost at 

 right angles to the others, and not nearly parallel with them as 

 in Dryosaurus. It agrees with the latter genus in having the 

 tibia longer than the femur. 



The only species of Dryosaurus at present known is the 

 type first described, and in future this may be called Dryo- 

 saurus altus. Several specimens of this Dinosaur are pre- 

 served in the Yale Museum, and they show it to have been 

 in life about twelve feet long, and one of the most slender 

 and graceful members of the group. The known remains 

 are all from the Atlantosaurus beds of Colorado and Wyoming. 



Laosaurus, Marsh, 1878. 



The present genus includes several species of diminutive 

 Dinosaurs, all much smaller than those above described, and 

 possessing many features now seen only in existing birds, 

 especially in those of the ostrich family. The two species of 

 the genus first described by the writer {Laosaurus celer, the 

 type, and L. gracilis)^ show these avian features best of all, 



* This Journal, vol. xvi, p. 415, plate ix, November, 1878. 

 f Ibid., vol. xv, p. 244, March, 1878. 



