CROCODILIA 277 



iininterruptedly throughout the long life of these cold-blooded 

 carnivorous reptiles. 



From the period of exclusion from the egg, the teeth of 

 the crocodile succeed each other in the vertical direction ; none 

 are added from behind forwards like the true molars in Mam- 

 malia. It follows, therefore, that the number of the teeth of 

 the crocodile is as great when it first sees the light as when it 

 has acquired its full size ; and, owing to the rapidity of their 

 succession, the cavity at the base of the fully-formed tooth is 

 never consolidated. 



The fossil jaws of the extinct Crocodilians demonstrate 

 that the same law regulated the succession of the teeth at the 

 ancient epochs when those highly-organised reptiles prevailed 

 in greatest numbers, and under the most varied generic and 

 specific modifications, as at the present period, when they are 

 reduced to a single family composed of so few and slightly 

 varied species as to have constituted in the system of Linnaeus 

 a small fraction of the genus Laccrta. 



The large, thick, externally ridged or pitted scales, though 

 common to the Crocodilian order, are not peculiar to them. 

 The labyrinthoclont Anisopus, the thecodont Staganolcpis, the 

 lacertian Saurillus, have left similar petrified scales. 



Crocodilians with eup-and-ball vertebrae, like those of 

 living species, first make their appearance in the greensand of 

 North America (Grocodilus basijissus and 0. basitruncatusy In 

 Europe their remains are first found in the tertiary strata. 

 Such remains from the plastic clay of Meudon have been 

 referred to G. isorhynckus, G. ccelorhynchus, G. Becquereli. In 

 tin- calcaire grossier of Argenton and Castelnaudry have been 

 found the G. Rallinati and G. Dodunii. In the coeval eocene 

 London clay at Sheppy Island the entire skull and charac- 

 teristic, parts of the skeleton of G. toliapicus and G. CTutinp- 



' " Lubyrinthodon scutulata*." Trans. Geol. Sue, 2d series, vol. vi. p. 538, 

 pi. 46. 



