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 Pteranodon 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 (37 

 feet). They were contemporaries of the Dinosaurs, several 

 forms, discovered by Marsh, occurring in the Cretaceous 

 beds of Kansas. 



CLASS VI. REPTILIA. 



Air-breathing Vertebrates, with limbs usually ending in daws; limbs 

 sometimes absent, rarely paddle-shaped ; 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. Theromorpha. Mammal-like sauriaus with solid pelvis and 

 shoulder-girdle, and with canine-like teeth, or toothless 

 and beaked. (Dkyuodon.) 



Order 2. Sauropterygia. Extinct colossal saurians, with long necks, 

 head of moderate size. (Plesiosaurus, Elasmosaurus.) 



Order 3. Ichtliyopterygia. Head large, orbits large; limbs paddle- 

 shiiped ; extinct forms. (Ichthyosaurus.) 



Order 4. Rhynchocephalia. Lizard-like; vertebrae bi-concave, species 

 mostly extinct. (Sphenodon.) 



Order 5. Ophidia. Body long, cylindrical, usually limbless; no shoul- 

 der-girdle. (Eutaenia.) 



Order 6. Pythonomorpha. Extinct, snake-like, limbs paddle-shaped. 

 (Mosasaurus.) 



Order 7. Lacertiiia. Body with a long tail; usually four limbs; mouth 

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



Order 8. G 1 heloma.Bo<\y enclosed in a thick shell, within which the 

 head and limbs can be withdrawn. (Testudo.) 



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. Pterosauria. Extinct flying saurians, with the fore limbs 

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

 (Pterodactylus.) 



