8 GUIDE TO REPTILES AND AMPHIBIANS. 



are other American members of the group, which was represented in 

 England by Pelorosaurus, Cetiosaurus, and Hoplosaurus or Ornithopsis. 

 Remains of these are shown in the Geological Department. 



Order III.— CROCODILIA. 

 (Cases 1-3.) 



The existing Alligators, Crocodiles, and Gharials, collectively 

 forming this order, are large, four-footed, long-tailed reptiles, with 

 teeth implanted in separate sockets, which are confined to the 

 margins of the jaws, and the quadrate-bone firmly fixed to the skull. 

 The bones of the skull are sculptured, and the body is covered with 

 large, horny shields, underlain on the back, and sometimes on the 

 chest, abdomen, and limbs, by pitted bony plates. The inner 

 aperture of the nostrils is situated very far back on the palate, thus 

 enabling these reptiles to breathe while holding their prey under water. 

 There are five toes to the fore-feet, and four to the hind-pair. 



In the skeleton, the bodies of the vertebrae unite by a ball-and- 

 socket joint, of which the ball is behind ; and the ribs articulate to 

 the vertebrae by two distinct heads. 



Species of true Crocodiles are found living in the New World as 

 well as in Africa and Asia ; the Alligators, with the exception of one 

 Chinese species, are American only, and the Gharials are Indian. 



In the earlier extinct members of the group, most of which were 

 marine, the inner aperture of the nostrils is situated less far back on 

 the palate ; and the vertebrae articulate with each other by nearly 

 flat or slightly cupped surfaces. A few of the early forms — notably 

 the Jurassic Metriorhynchus and Oeosaurus — had no bony plates on 

 the back. The early Crocodilia include long-snouted (Pelagosaurus, 2) 

 and short-snouted types (Goniopholis, 4), which may perhaps have 

 respectively given rise to the modern Gharials and Crocodiles. In 

 these Jurassic Crocodiles the position of the posterior nostrils is 

 intermediate between that obtaining in modern Crocodiles and the 

 Triassic Parasuchia (Phytosaurus, \), in which last they open almost 

 immediately below the external nostrils. These very primitive 

 Crocodilia show such a decided approximation to the extinct 

 Dinosauria as to indicate a close connection between the two 

 groups ; they are also related to the Rhynchocephalia. 



The family Crocodilida is taken to include all the existing 

 members of the order Crocodilia. The group is characterised by 

 the bodies of the neck-vertebrae articulating by cup-and-ball joints, 



