266 Dr. J. E. Gray on the Species of Crocodiles. 



face is very short ; it elongates as the animal grows, at first 

 very gradually, and, at length, assumes the typical form of the 

 species when the animal has reached about one-fourth or one- 

 third of its natural size. The head continues to increase in 

 firmness and strength ; and when the animal has attained nearly 

 its adult size, the bones of the head become thickened, the face 

 becomes broader and higher, and the general form of the head 

 is considerably altered. Thus the half-grown specimens give the 

 most characteristic form of the species. 



I have noticed that there is considerable variation in the width 

 of the face in specimens from different localities, but which 

 appear in other respects to belong to the same species. Some 

 naturalists might be inclined to regard them as distinct species ; 

 but in our series, large as it is, we have not sufficient materials to 

 decide the question with any confidence. Perhaps, if the skulls 

 of specimens from each locality could be compared, other cha- 

 racters might be found; but this must be left for my successors 

 in this field of research. 



I may remark that the observation of MM. Dumeril and 

 Bibron (Erp. Gen. 25 & 47), that Crocodiles are not found in 

 Australia, and that the American Crocodiles are confined to the 

 islands of that continent, is no longer consistent with fact; in- 

 deed, long before the publication of their work, various travellers 

 had recorded the occurrence of Crocodiles on the north coast 

 of Australia; and we have received specimens of the skull of 

 Oopholis porosus from thence. 



The genera here proposed have the following geographical 

 distribution : — 



Asia and Northern Australia : Oopliolis and Bombifrons. 

 Africa : Crocodilus, Halcrosia, and Mecistops. 

 Tropical America : Palinia, Molinia. 



The skulls of Crocodiles may be arranged thus : — 



1. Nasal bone produced, and separating the nostril into two 

 parts. Halcrosia. 



2. Nasal bone produced, and dividing the edges of the nostril. 

 Oopliolis, Crocodilus, Molinia (americana) , Bombifrons, Palinia. 



3. Nasal bone not reaching the nostril. Molinia {intermedia), 

 Mecistops. 



The large front teeth of the Gavials fit into a notch in the 

 front of the upper jaw, and the canines into a notch also. In the 

 Crocodiles the canines fit into a notch, as in the Gavials, but the 

 large front teeth fit into a pit or perforation in the front of the 

 upper jaw ; and in the Alligators both the canines and large front 

 teeth fit into pits or perforations in the edge of the upper jaw. 



