CLASSIFICATION OF REPTILES. 517 



Rhamphorhynchus had teeth in the back of the jaw, the 

 ends of the jaws being toothless and probably encased in 

 horny beaks, while in Pteranoilon the jaws were toothless. 

 They were of different size, some expanding only as much 

 as a sparrow, others with a spread of about nine metres (27 

 feet). They were contemporaries of the Dinosaurs, several 

 forms, discovered by Marsh, occurring in the Cretaceous 

 beds of Kansas. 



CLASS V. REPTILIA. 



Air-breathing Vertebrates, icith limbs usually ending in claws ; limbs 

 sometimes absent, rarely paddlc-shxped ; body scaled ; ribs well developed ; 

 heart in the highest forms four-chambered ; cold blooded ; an incomplete 

 double circulation ; oviparous; eggs large; embryo with an amnion and 

 allantois ; no metamorphosis. 



Order 1. Ophidia. Body long, cylindrical, usually limbless ; no shoul- 

 der girdle. (Eutsenia.) 



Order 2. Fythonomorpha. Extinct, snake-like, limbs paddle-shaped. 

 (Mosasaurus.) 



Order 3. Lacertilia. Body with a long tail; usually four limbs; mouth 

 not dilatable, the bones of the jaw being firm. (Sceleporus.) 



Order 4. Chelonia. Body enclosed in a thick shell, within which the 

 head and limbs can be withdrawn. (Testudo.) 



Order 5. Rhynchocephalia. Lizard-like ; vertebrae bi-coucave, species 

 mostly extinct. (Sphenodon.) 



Order 6. Ichthyopterygia. Head large, orbits large ; limbs paddle- 

 shaped ; extinct forms. (Ichthyosaurus.) 



Order 7. Theromorpha. Mammal-like saurians with solid pelvis and 

 shoulder-girdle, and with canines, or toothless and beaked. 

 (Dicynodon.) 



OrderS. Sauroptcrygia. Extinct colossal saurians, with long necks, 

 head of moderate size. (Elasmosaurus.) 



Order 9. Crocodilia. Thick - scaled ; heart four-chambered. (Croco- 

 dilus.) 



Order 10. Dinosauria. Colossal extinct saurians, capable of rising 

 and resting on the hind legs, and making three-toed tracks. 

 (Hadrosaurus.) 



Order 11. Ptcrosauria. Extinct flying saurians, with the fore limbs 

 largo and a very long ulnar finger; toothed or toothless. 

 (Pterodactyl us.) 



