54 vertebrata. 



Order 1 — Satjria. 



The Saurians are distinguished by an elongate, rounded body 

 densely covered with scales or plates ; an elongate, tapering, usually 

 scaly tail; four limbs (occasionally rudimentary); distinct ribs and 

 sternum; one occipital condyle; and a mouth not dilatable. 



The Deinosaurians — the highest and most terrible of Reptiles — 

 are distinguished by four well-developed, unguiculate limbs, a medullary 

 cavity in the bones of the extremity, five anchylosed sacral vertebras, a 

 twofold articulation of the ribs, broad coracoids, and long slender clav- 

 icles. They first appear in the upper member of the Lower Lias, and 

 are now extinct. 



The Eiialiosaicrians were those marine, air breathing, carnivorous 

 Lizards that swarmed in such prodigious numbers during the Secondary 

 epochs. In many respects they were intermediate between the Chelonia 

 and Crocodilia ; but the skin was probably naked. The skeleton is dis- 

 tinguished by the numerous biconcave vertebrae, a single occipital con- 

 dyle, the position of the nostrils at or near the summit of the head, 

 large teeth set in a groove or in sockets, and the many short, flat finger- 

 bones. The group began in the Muschelkalk. 



The Pterosaur ians, or " Pterodactyles," are among the strangest 

 creatures brought to light by Geology. They had the claws and teeth of 

 a Reptile ; the body and tail of a Mammal ; beak, hollow bones and keeled 

 sternum of a Bird ; and a development of the forelimbs for wings like 

 those of the Bat. They furnish the first example of the procoelian type 

 of vertebrae. The teeth are implanted in distinct sockets. The oldest 

 Pterodactyles are from the Lower Lias ; the largest occur in the Upper 

 Grreensand ; but the best^ defined and most numerous specimens come 

 from the Middle Oolite. 



The Crocodiles are covered with a cuirass of square plates placed 

 in longitudinal lines; the jaws are united into a solid mass ; the pre- 

 niaxillary is double ; the teeth are set in sockets in a single row ; the 

 vertebrae of Cretaceous, Tertiary and living species, are concavo-convex, 

 of all others, either doubly flat, doubly concave or convexo-concave. In 

 extinct species there are two nasal apertures ; in recent forms, only one. 

 Crocodiles have existed since the Lias Period. 



The True Lizards have scales, one premaxillary, lower jaws united 

 by a suture, teeth set in a groove (in certain extinct forms, in sockets), 

 vertebrae concavo-convex, skull projecting in a ridge over the eyes, and 

 two external nostrils. The earliest representation of the true lacertian 

 type occurs in the Upper Oolite. But the Thecodont Reptiles, which 

 agree in many respects with the amphicoelian Crocodiles, but combine 



