198 DINOSAURS OF NORTH AMERICA. 



forms, and to tbis character the name Camptonotus, first given to the 

 genus by the writer in 1879, especially refers. Another notable feature 

 of the sacral vertebrae of the type specimen should be mentioned. The 

 vertebrae of the sacrum, especially the posterior four, are joined to each 

 other by a peculiar peg and-notch articulation. The floor of the neural 

 canal of each vertebra is extended forward into a pointed process 

 (somewhat like an odontoid process), which tits into a corresponding 

 cavity of the centrum in front. This arrangement, while permitting 

 some motion between the individual vertebra?, helps to hold them in 

 place, thus compensating in a measure tor absence of anchylosis. A 

 similar method of articulation is seen in the dermal scales of some 

 ganoid fishes, but so far as the writer is aware nothing of the kind has 

 been observed before in the union of vertebra?. 



In Camptosaurus the sternum was entirely unossified, and no trace 

 of clavicles has been found. The pelvis of Camptosaurus differs 

 especially from that of Iguauodou in the pubis, the postpubic branch 

 being even longer than the ischium, while in Iguanodon this element is 

 much shortened. 



In the fore foot of Camptosaurus there were five functional digits, 

 the first being flexible and nearly parallel with the second, thus differ- 

 ing from the divergent, stiff thumb of Iguanodon. The hind feet had 

 each three functional digits only, the first being rudimentary and the 

 fifth entirely wanting, as shown in PI. LVI. The entire skeleton of 

 < lamptosaurus was proportionately more slender and delicately formed 

 than that of Iguanodon, although the habits and mode of life of these 

 two herbivorous dinosaurs were doubtless very similar. 



The type specimen of Camptosaurus dispnr, used as the basis of the 

 present restoration, is from the Atlaiitosaurus beds of the Upper 

 Jurassic of Wyoming. This species and other allied forms will be 

 described in full in an illustrated memoir now in preparation by the 

 writer for the United States Geological Survey. The present restora- 

 tion is reduced from a large drawing made for that volume. 



LAOS A URIDsE. 

 DRYOSAURUS. 



Another genus of Jurassic dinosaurs, allied to Camptosaurus, but 

 differing from it in many important respects, is Dryosaurus. The type 

 was described by the writer in 1878 under the name Laosaurus altus, 

 and a tooth, the pelvis, and a hind leg were also figured. Additional 

 material since received shows that this genus is quite 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 only species of Dryosaurus at present known is the type first 

 described, and this form is now called Dryosaurus altus (PI. LV, 

 tig. 4). Several specimens of this dinosaur are preserved in the Yale 



