THE GALAPAGOS ISLANDS 



279 



ahingdonii recently discovered on Abingdon Island, as well 

 as one extinct species, T. ephippium, found on Indefatigable 

 Island. These are all of very large size, like the gigantic 

 tortoises of the Mascarene Islands, from which, however, 

 they differ in structural characters ; and Dr. Giinther 

 believes that they have been originally derived from the 

 American continent.-^ Considering the well known tenacity 

 of life of these animals, and the large number of allied 

 forms which have aquatic or sub-aquatic habits, it is not 

 a very extravagant supposition that some ancestral form, 

 carried out to sea by a flood, was once or twice safely 

 drifted as far as the Galapagos, and thus originated the 

 races which now inhabit them. 



The lizards are five in number ; a peculiar species of 

 gecko, Phyllodadylus galap)ctgensis, and four species of 

 the American family Iguanidse. Two of these are distinct 

 species of the genus Tropidurus, the other two being large, 

 and so very distinct as to be classed in peculiar genera. 

 One of these is aquatic and found in all the islands, swim- 

 ming in the sea at some distance from the shore and 

 feeding on seaweed ; the other is terrestrial, and is confined 

 to the four central islands. These last were originally 

 described as AmMyrhynclius cristatus by Mr. Bell, and 

 A. siibcristatus by Gray ; they were afterwards placed in 

 two other genera Trachycephalus and Oreocephalus {sec 

 Brit. Mus. Catalogue of Lizards), while in a recent paper 

 by Dr. Steindachner, the marine species is again classed as 

 Amblyrhynchus, while the terrestrial form is placed in 

 another genus Conolophus, both genera being peculiar to 

 the Galapagos. 



How these lizards reached the islands we cannot tell. 

 The fact that they all belong to American genera or 

 families indicates their derivation from that continent, 

 while their being all distinct species is a proof that their 

 arrival took place at a remote epoch, under conditions 

 perhaps somewhat different from any which now prevail. It 

 is certain that animals of this order have some means of 

 crossing the sea not possessed by any other land vertebrates, 



1 Gigantic Land Tortoises Living and Extinct in the Collection of the 

 British Museum. By A. C. L. G. Gunther, F.R.S. 1877. 



