CLA8SIFIGATI0N OF BEPTILES. 517 



Rliamphorliynchus 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 abont 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-breatJiing Vertebrates, with Urahs usually ending in claws ; limbs 

 ■sometimes abseiit, rarely padcUe-shaped ; body scaled ; ribs well developed ; 

 heart in the Highest forms four-ehambered ; cold blooded ; an incomplete 

 •double circulation,; oviparous; eggs large; embryo icith an amnion, and 

 Mllantois ; no metamorphosis. 



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

 der girdle. (Eutaenia.) 



'Order 2. Pythonomorpha. — Extinct, snake-like, limbs paddle-slii^ped. 

 (Moaasaurus.) 



■Order 3. Lacertilia. — Body with a long tail; usually four limbs; n\outh 

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



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

 head and limbs can be witlidrawn. (Testudo.) 



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

 mostly extinct. (Sphenodon.) 



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

 shaped ; extinct forms. (Ichthyosaurus. ) 



■Order 7. Theromorpha. — Mammal-like saarians with solid pelvis and 

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

 (Dicynodon.) 



Orders. Sauropterygia. — 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. Pterosauria. — Extinct flying saurians, with the fore limbs 

 large and a very long ulnar finger; toothed or toothli-ss. 

 (Pterodactylus.') 



