Structure of the Fossil Sanrians, 285 



bones of species of living crocodiles sent to him by Sir Stam- 

 ford Raffles, that the epiphyses of the bones of young animals 

 have been cartilaginous, and that hence it may have oc- 

 curred that the vertebrae have been deprived of their con- 

 vex surfaces, is no farther applicable to this concavity of 

 the posterior surface. Vertebrae, whose posterior surfaces 

 are convex, occur, for the most part, in the tertiary beds. 

 A few examples only of such vertebrae from older beds 

 are known, and these occur in the more recent secondary 

 formations; for instance, the fossil remains of an actual 

 crocodile (C. Harlani), which Harlan describes from a 

 marl of North America, probably belonging to the green 

 sand formation.* This fossil crocodile is distinguished most 

 strongly from other crocodiles by the greater thickness of 

 the teeth with relation to their length; in perfect accord- 

 ance with which circumstance are the very short, thick, and 

 blunted teeth, it being the young teeth only which are of a 

 pointed and conical form. The teeth, also, are more cy- 

 lindrical, and there are fewer in a given space than in the 

 Crocodilus acutus or C. Lucius ; the distance, also, from the 

 fourth tooth (which is comparatively very large) up to the 

 outer edge of the symphysis is twice as great in the fossil 

 Crocodile as in the above-mentioned living species. Such 

 peculiarities would justify us in constituting a new subgenus 

 of the creature to which this fragment of a jaw belonged. 

 Several vertebrae were also found in the same spot, which, 

 according to the engravings, possess a concave, as well as a 

 decidedly convex, surface, as in the living Crocodiles. None 

 of them are sufficiently long to have appertained to this indi- 

 vidual ; while they differ from those compared with them, in 

 particular by a peculiar compression on the side and under 

 parts of the body. Mantell f also mentions that his collec- 

 tion contains three very small vertebrae, which are from the 

 Wealden beds, older than the tertiary formation, and which 

 are concave before and convex behind, as in the living 

 iguana4 



It is not to be denied, that the difference in the organs 

 of locomotion in the fossil and the living Saurians is, at 

 first sight, surprising; but this circumstance arises only 

 from our not being accustomed to see the former in the 

 living types. We should be equally astonished if we only 



* Journ. of Philad., iv. p. 21. t. 1. 



f fflust. Geol. Sus., p. 77. 



X These prove to have belonged to turtles ; but Dr. Mantell has re- 

 cently discovered several large vertebras of the true crocodilian type ; that 

 is, concave anteriorly, and convex posteriorly. — Ed. 



Y 3 



