EXTINCT ORDERS OF REPTILES. 



237 



enormous reptiles walked upon all-fours ; and it seems not 

 unlikely that their habit of existence was really a semi- 



rig. 579 — Anterior dorsal vertebi a of (-/( t li ti ioms (Camc/rosoKrws) swpremws, reduced 

 in size and viewed from behind (After Cope ) Cieta&eous, Korth America. 



aquatic one. The Amphicoelias of the Cretaceous of ISTorth 

 America is nearly allied to Chondrosteosaurus, and the Dystro- 

 phoeus of the Trias of Utah seems to have belonged to the 

 same group. 



It would seem that the genera just mentioned belong to 

 the same natural group of the Deinosaurs as those which 

 Marsh has recently raised to the rank of a sub-order under 

 the name of Sauropoda. The genera in question {Atlanto- 

 saurus, Moroscmncs, &c.) are from the Jurassic rocks of 

 America, and are characterised ■ by the nearly equal size of 

 the fore and hind limbs, the feet being pentadactylous and 

 plantigrade, and the limb-bones without medullary cavities. 

 The carpal and tarsal bones are distinct; the pubes unite in 

 front by a ventral symphysis ; the pr?ecaudal vertebrae con- 

 tain large cavities, possibly pneumatic ; and the neural arches 

 are united to the centra by suture. 



