VERTEBRATA. 207 



Order V. SAUKOPTERYGIA. 



PLESIOSAURIA. 



Limbs paddle-like, formed for swimming. Vertebras with their 

 articulating surfaces flat or slightly concave. Neck mostly very 

 long. A sacrum of two bones. No sternum. 



The jaws were produced, but the nostrils were placed far back 

 near the orbits ; the teeth were lodged in distinct sockets, and, 

 except in Placodus, were of the normal character. The eye had 

 no bony plates. The scapula resembled the scapula of Chelonia. 



This order contains Mesozoic marine lizards, generally of large 

 size. 



*Nothosaurus. *Plesiosauru3. *Placodus. 



*Simosaurus. 



Order VI. PTEEOSAUEIA. 



Forearm and fifth digit very long, formed for flight. Vertebrse 

 procoelous. Jaws prolonged; teeth conical, lodged in distinct 

 sockets. 



The long bones and vertebra? had air-cells, as in birds. The 

 neck was very long ; and there was a sternum with a mesial crest. 

 For these and other reasons, Prof. H. G. Seeley thinks them 

 more nearly allied to birds than to reptiles ; and he proposes for 

 them a class which he names Saurornia. 



These flying lizards of the Mesozoic period seemed to have been 

 confined to mid-Europe. One appears to have had an expanse of 

 wing of more than twenty feet. 



Marsh has recently described a new form (Pteratiodori) allied to 

 this order found in the Cretaceous beds of Kansas. It is without 

 teeth, and constitutes, according to him, a distinct order and a 

 distinct family. 



*Ramphorhynchus. *Dirnorphodon. *Pterodactylus. 



Order VII. DINOSAURIA. 

 ORMTHOSCELIDA. PACIIYPODA. 



Teeth lodged in distinct sockets. Vertebrae mostly flat on their 

 articular surfaces, a few anterior opisthocrelous. Limbs ambu- 

 latory. Exoskeleton consisting of bony plates in some, in others 

 only a naked skin. 



