LACERTILIA. 



305 



Iii the two preceding genera the alveolar borders of the 

 jaws have an uneven or wavy contour, and the teeth are of 

 unequal size. 



In the gavials (genus Gavialis) the teeth are nearly equal 

 in size and similar in form in both jaws, and the first as well 

 as the fourth tooth in the lower jaw passes 

 into a groove in the margin of the upper 

 jaw, when the mouth is closed. The number 

 of teeth is always greater in the gavials than 

 in the crocodiles or alligators. The first five 

 pairs of teeth above are supported by the pre- 

 maxillary bones ; the first, second, and fourth 

 of the lower jaw are the longest. The eight 

 or nine posterior teeth are nearly conical, the 

 rest are sub-compressed, ant ero -posteriorly, 

 and present a trenchant edge on the right and 

 left side, between which a few faint longitu- 

 dinal ridges traverse the basal part of the en- 

 amelled crown (fig. 105). The position of the 

 opposite sharp ridges, and the direction of the 

 flat sides of the crown, are at right angles to 

 the above, in the extinct amphiccelian gavial Teeth of the Gavial. 

 (SucJwsaurus cultridens), which in other respects most nearly 

 resembles the gangetic gavial in the form of the teeth. 



Orocodilians with cup-and-ball vertebrae, like those of 

 living species, first make their appearance in the greensand of 

 North America (Crocodilus basifissus and C. basitruncatus). In 

 Europe their remains are first found in the tertiary strata. 

 Those from the plastic clay of Meudon have been referred to C. 

 isorhynclius, C, ccelorhynchus, C. Becquereli : those from the cal- 

 caire grossier of Argenton and Castelnaudry to the C. Rallinat 

 and C. Doclunii. In the coeval eocene London clay at Sheppy, 

 the entire skull and characteristic parts of the skeleton of C. 

 toliapicus and C. Champsoides occur. ' In the somewhat later 



