42 HELLER 



On June 26, 1899, we took final leave of the Galapagos and 

 headed for Cocos Island, where we arrived three days later and 

 anchored in Chatham Bay. Here we stayed four days. On 

 account of the dense vegetation only the coast and water courses 

 could be explored. From Cocos we set sail, July 2, for San 

 Francisco and after a short stop of one day, August 3, at Clar- 

 ion Island, Revillagigedo Archipelago, we reached San Fran- 

 cisco on August 30, 1899, having been gone 304 days. 



Material. — The material on which the present paper is based 

 consists of nearly 1,200 specimens, being perhaps the largest 

 collection of reptiles yet secured from the Galapagos Archi- 

 pelago. With this collection as a basis, the attempt is here made 

 to describe all species collected, with descriptions of their varia- 

 tions and habits, and to give the ranges and the synonymy of 

 all the forms known to inhabit the Galapagos Archipelago and 

 Cocos and Clipperton Islands. 



Geologic Formation. — The Galapagos Archipelago is chiefly 

 composed of basaltic lava and tufa, the latter, wherever it 

 occurs, underlying the lava and forming the older portions of 

 the islands. The fluidity and low melting point of the basaltic lava 

 has given to the islands their characteristic topography, that is, 

 comparatively low volcanoes with gently sloping sides and im- 

 mense craters several miles in diameter. This formation is best 

 exhibited on Narboro, Albemarle, Indefatigable and Bindloe, 

 which are the only islands with large central craters. The craters 

 on Charles, Chatham, James, Duncan, Jervis, Barrington and 

 Abingdon are much smaller, being mere potholes in compari- 

 son with those of Albemarle. Definite craters are lacking on 

 Hood, Tower, Wenman and Culpepper. 



Subsidence Theory. — All the islands are obviously of vol 

 canic origin, yet Dr. Baur^ invokes a continental origin or con- 

 nection to explain their faunal characteristics. To account for 

 the presence of representative species on each island he as- 

 sumes that all the islands in the group were formerl}-- connected, 

 forming one island, and that the species were generally distrib- 

 uted over this connected area before submergence ; isolation 

 and changed conditions after submergence are deemed by Dr. 



1 Baur, Biol. Lect. Woods Hole, pp. 67-7S, 1S94. 



