Or A HIGHER FORM OP LIFE ON A LOWER FORM. 427 



Crocodilia. But in the vertebral, the dermoskeletal, and the palato- 

 narial characters there is no known exception to the modifications 

 which severally characterize the amphicoelian and proccelian 

 Crocodiles. 



We find, as the Secondary approach the Tertiary periods, that the 

 Goniopholis, for example, of the Purbeck and Wealden series 

 shows a nearer approach, in the shortness and breadth of the facial 

 part of the skull, to the majority of the Tertiary and existing Cro- 

 codiles than the Oolitic and Triassic amphiccelians exhibit ; while 

 the long and narrow jaws, with the series of small, sharp, uniformly- 

 sized teeth, in a straight row, common to Teleo- and Steneo- 

 saurians are now exceptionally manifested by the single genus 

 Gavialis, with a very limited geographical range. Such forms and 

 proportions of the jaws and teeth, with some minor dermal modifica- 

 tions affecting scutes and foot-webs, justify the generic status of 

 the Indian Gharrials. 



The claims of the American Alligators to generic honour rest .on 

 feebler foundations ; and in regard to the procoelian Crocodiles of 

 the present day, the work of what our German friends have termed 

 the " Gattungsmacherei," has been most productive. Tomistoma, 

 Oopholis, Halcrosia, Palceosuchus, Rliynchosuchus , Rhamphostoma, 

 Mecistops, Bombifrons, Palinia, Molinia, Caiman, and Jacare hardly 

 exhaust the multitude of names generic with which herpetology 

 has been encumbered. What is of main importance to know is, 

 that all the Crocodiles bearing the above names have the following 

 characters in common : — the upper temporal apertures smaller than 

 the orbits ; the palato-nares small, formed by the pterygoids exclu- 

 sively, placed far back and on a slope towards the occiput ; the ver- 

 tebrae procoelian. 



These Crocodiles vary in respect to the proportions of length to 

 breadth of skull, in the relative length of the nasal bones, in the 

 proportions and course of sutures of the premaxillaries, in the 

 degree of difference of the size of the teeth in the same species, 

 and in the relation of some of the larger lower teeth to the 

 upper jaw when the mouth is shut, also in the number and ar- 

 rangement of the dermal scutes and in the extent of the toe-webs. 

 And such characters are available, by their observed constancy, in 

 the discrimination of the existing species of Crocodilia. 



The connoting of the more essential characters common to the 

 procoelian series, and of those which in like manner were common 

 to the amphicoelian series, has led to the consideration of the con- 

 comitant and seemingly influential conditions of such respective 

 organic characters, more especially of the relation of the procoelian 

 modifications to the coming in of the mammalian class, and perhaps 

 to the going out of certain members of the reptilian class : and such 

 considerations are now submitted to the judgment of the Geological 

 Society. 



