§25. 



CROCODILES. 571 



as the Carboniferous system. Throughout the Oolitic, 

 Wealden, and Cretaceous epochs, terrestrial ?, marine, and 

 fresh-water Chelonians abounded. From the most ancient 

 Tertiary to the present time, the three groups of this order 

 of reptiles have flourished. Their remains are associated 

 with those of the Sivatherium, &c. in the Sub-Himalayahs, 

 of the Mastodons in the Burmese empire, of Palaeotheria 

 in the Paris and London basins, and with fruits and 

 tropical plants in the Isle of Sheppey : their bones and 

 eggs are daily imbedded in the recent conglomerates of 

 the Isle of Ascension. The remains of living species of 

 Indian land tortoises are collocated with the bones of the 

 most ancient extinct eocene mammalia in the Sewalik 

 hills.* 



25. Crocodiles. — This family of loricated or mailed 

 saurian reptiles, contains the only living types that at all 

 approach in magnitude the colossal forms of the secondary 

 epochs. The Egyptian Alligator, as is well known, attains 

 a large size ; and the long and slender-beaked crocodilian 

 reptile of India, the Gavial of the Ganges, sometimes reaches 

 a length of nearly thirty feet. The peculiar character of 

 the teeth of these animals, and their mode of increase and 

 renovation, have already been pointed out (ante, p. 414). 

 The vertebrae, or bones of the back, are concavo-convex ; 

 l. e. united to each other by a ball and socket joint, the con- 

 vexity being behind. Some of the fossil crocodiles of the 

 tertiary also have this structure of the spinal column ; but 

 in every crocodilian of the secondary formations, the articu- 

 lating surfaces of the vertebrae are either flat or concave ; 

 except in one genus (Strept.ospondylus, ante, p. 414 f), in 

 which the vertebrae are convexo-concave, i. e. the con- 

 vexity is directed forwards ; a position the reverse of the 

 ordinary type. J Reptiles of the crocodilian order, but be- 

 longing to several extinct genera, swarmed throughout the 



* Dr. Falconer and Major Cautley. t Medals, p. 725. J Ibid. p. 718. 



