ALLIGATORS, GAVIALS, FOSSIL CROCODILES. 551 



bellowing, not unlike that of a bull. At the approach of winter 

 the North American species bury themselves in holes in the 

 earth, and pass the cold weather in a state of torpidity. Several 

 species of Alligator are known ; varying in length from two to 

 more than twenty feet. Several species of Crocodiles are found 

 in a fossil state ; some of them having been much larger than 

 any now existing. It is interesting to remark, that remains of 

 forms allied to the Gavials are found in the same strata with 

 those of the Ichthyosaurus and Plesiosaurus ; which strata are, 

 geologically speaking, much older than those in which the re- 

 mains of Mammals occur. It is in these last that we find relics 

 of Sauria resembling the Caymans of the present time ; and this 

 is in accordance with the general rule, that the terrestrial animals 

 were the last to make their appearance on the surface of the 

 globe. Some of the fossil Crocodiles belong to the same family 

 as the existing species, having the posterior surface of the bodies 

 of the vertebra convex ; whilst others, such as the Steneosau- 

 rus, had the convexity on the anterior surface, and the gigantic 

 Teleosaurus had both surfaces concave, like those of the ordinary 

 fishes. 



489. In the Jurassic strata, in which the most remarkable of 

 these extinct Crocodiles first make their appearance, we also 

 meet with the remains of numerous gigantic Reptiles, which appear 

 to have been most nearly related to the Crocodiles, although 

 they had smooth skins, quite destitute of the bony plates charac- 

 teristic of the Loricata. They have been formed by some na- 

 turalists into a distinct order, under the name of ENALIOSAURIA. 

 Of these the ICHTHYOSAURI, or Fish-Lizards, from their whole 

 organization evidently hold an intermediate position between the 

 Reptiles, Fishes, and Cetaceous Mammalia. The spinal column 

 is formed upon the plan of that of a Fish ; the vertebras being 

 concave on both surfaces, and having had a bag of fluid inter- 

 posed between each pair ( 66) ; and the arches which enclosed 

 the spinal cord always remained distinct from the bodies. Hence 

 the body must have had great flexibility, and must have been able 

 to move rapidly through the water by its undulations from side 

 to side? assisted probably by a broad fin-like expansion of the 



