328 GEOGRAPHICAL AND GEOLOGICAL DISTBIBUTION. 



former, as understood by most systematists, are comprised in two . 

 genera, Gavialis (with a single species, G. Gangeticus), restricted 

 to the waters of the Indian Peninsula, and Tomistoma, a Bornean 

 form, whose range probably extends to North Australia. 



The true crocodiles, of which some authors recognise two gen- 

 era, Crocodilus and Mecistops,* inhabit nearly all the larger streams 

 (and many of the lakes) of Africa, India, and the north coast of 

 Australia. Although for a long time supposed to be entirely want- 

 ing in the New World, they are now known to inhabit the waters 

 of tropical America on both sides of the Andes (Ecuador, Colombia, 

 the Orinoco, &c.), extending their range to Mexico and the West 

 India Islands (Cuba, San Domingo, Jamaica). Crocodilus Ameri- 

 canus enters some of the streams of Florida. The species having 

 the broadest distribution appear to be Crocodilus porosus, whose 

 range embraces the area included between the North Australian 

 coast, the Indian Peninsula, and China, and C. Vulgaris, the com- 

 mon African form, which is found throughout the greater part of 

 the continent, and which has been reported, although doubtfully, 

 also from Palestine. Two species of crocodile, C. robustus and C. 

 Madagascariensis, the one related to the common Indian form and 

 the other to the African, are found on the island of Madagascar. 



The alligators (Alligator), also known as caymans and ^'acarSs, 

 and comprising, according to some authors, not less than ten dis- 

 tinpt species, are confined to the waters of tropical and sub- tropical 

 America, ranging from the Argentine Republic to Tennessee. The 

 single species of the United States is the Alligator Mississippiensis. 

 It is not a little surprising, seeing the presence there of crocodiles, 

 that alligators should be almost wholly absent from the West In- 

 dies; one species (A. latirostris) is said to inhabit the island of 

 Guadeloupe. 



Geologically the crocodiles represent an ancient group, dating 

 their first appearance, as far as is yet known, from the Triassic pe- 

 riod. Three genera of this age are recognised : Stagonolepis, from 

 the Elgin sandstones of Scotland, Belodon, from Wtirtemberg, the 



* Dr. Gray, in his " Catalogue of the Shield Reptiles of the British Mu- 

 seum" (1872), makes seven genera, of which Oopholis is Asiatic and Austra- 

 lian, Bombifrons Asiatic, Palinia and Molinia American, and the remainder, 

 Crocodilus, Halcrosia, and Mecistops, African. It is questionahle whether 

 any of these forms is entitled to generic distinction. 



