196 REPTILES OF THE GALAPAGOS. [CH. IV 



are also, on Charles Island, remains of older volcanic 

 formations, which recur in one or two of the smaller 

 islands. All the islands of the archipelago are placed 

 within the 1000 fathom line. They were first discovered 

 in the sixteenth century. 



Mammalian life is not entirely wanting, but it is 

 scarce, in these islands. At present we are only acquaint- 

 ed with two species; one of these is a mouse belonging 

 to the American genus Hesperomys, which may or may 

 not be indigenous. The other mammal is a bat ; but our 

 knowledge is here not accurate ; for the bat has been only 

 seen and not collected. 



There are on the other hand a good many reptiles. 

 The most famous are of course the huge tortoises, which 

 have given their name to the archipelago; there is no 

 doubt that these bulky creatures, which sometimes reach 

 a weight of 700 pounds, are truly indigenous; for they 

 were seen by the Spaniards who discovered the islands. 

 The peculiar thing about these tortoises is that different 

 islands are characterised by different species. There are 

 in all six species of these Chelonians, but the exact 

 locality of one or two is not known. 



Tortoises however are not the only reptiles which live 

 in or round these islands. Four genera of Lizards exist 

 there ; these are Tropidurus, Conolophus, Amblyrhynchus, 

 and the Gecko Phyllodactylus. 



Of the genus Tropidurus there are altogether eight 

 species on the islands, each island as in the case of the 

 tortoises having its own peculiar form. Amblyrhynchus is 

 a marine genus feeding on seaweeds ; it is like the last a 



