THE SUBCLASS PARAPSIDA 



255 



Family Mesosauridae. Lower Permian. Slereosternum Cope 

 {Notosaurus Marsh), Mesosaurus Gervais, Brazil. Mesosaurus Ger- 

 vais {Ditrichosaiiriis Gurich), ? Noteosaurus Broom, South Africa. 



Fig. 176. Restoration of Mesosaurus. After McGregor. The posture of the hind leg is 



slightly modified. 



9. ORDER ICHTHYOSAURIA 



Marine reptiles with all aquatic adaptations of the tail-propelling 

 type: elongated face; posterior nares, sclerotic plates, short neck, 

 elongated body, no sacrum, long, flattened or dilated tail, short pro- 



