in North America of rare Extinct Vertebi'ates. 215 



the most trustworthy and acceptable guides to the true nature 

 and way of life of the stupendous Saurian of the Dakota hori- 

 zon. As a Bothriospondyliau genus the side-pits may have 

 received, as I have suggested, saccular portions of the lung ; 

 and the service derived therefrom might be such as the Gadus 

 navaga receives by the extension of sacculi of the air- 

 bladder into the excavations of the parapophyses of its abdo- 

 minal vertebra? — a diminution, viz., of specific gravity facili- 

 tating natation. 



To the functions with which the further extension of air 

 into the osseous tissue is related, the degree of solidity 

 ascribed to the limbs of Condrosteosaiirus would be adverse. 

 In that limb-character I see the affinity of the genus to 

 Cetiosaurus. In that genus, in Iguanodon, and in Scelido- 

 saurus the fore limbs manifest the proportions which least 

 impede the faculty of swimming exercised by the powerful 

 hind limbs and tail. From the quantity of unossified tissue 

 in the vertebral column, and from the restriction, as a Dino- 

 saur, of the number of sacral vertebrte, I infer that Ghon- 

 drosteosaurus was more aquatic, less terrestrial, in its life and 

 movements than were the Iguanodon and Megalosaurus. 



It is as interesting as it was unexpected to possess the 

 knowledge of the extensive geographical range of the hugest 

 of the hitherto characterized extinct Reptilia. 



As to the geological position of the American representative 

 of our Wealden Ghondrosteosaurus , Prof. Marsh sees grounds 

 for identifying what is, according to Prof. Mudge, the same 

 horizon as the Dakota with the Wealden of England. But 

 Prof. Cope remarks : — ^' Specimens from the northern locality 

 which I have examined render it certain that the horizon is 

 that of Mr. Lucas's excavations. Of this I may say that 

 there is no palseontological evidence of its identity with the 

 Wealden. The resemblance of the vertebrate fossils to those 

 of the English Oolite is much greater, but not sufficient as yet 

 for identification. The discovery of Vertebrata in the strata 

 of the Dakota epoch is an important addition to the geology 

 and palaeontology of North America""^. 



If, however, the legitimate inference from the above detailed 

 conformity of characters between Ghondrosteosaurus and 

 Camarosaurus be accepted, it will supply an evidence of the 

 accuracy of Prof. Marsh's inference as to the Wealden age of 

 the Dakota formation. 



also in an especial manner for the skill and care he has exercised in 

 taking out and shipping the ponderous specimens " (Proc. Amer. Philos. 

 Soc. 1877, p. 234). 



* Proc. Amer. Phil. Soc. 1877, p. 234. 



