Vol. II, Pt. I] VAN DENB URGH—SLEVIN—GALAPAGOAN LIZARDS 139 



1. T. paciUcus Abingdon Island 



2. T. duncanensis Duncan Island 



3. T. habelii Bindloe Island 

 A..T. bivittatus Chatham Island 



5. T. delanonis Hood and Gardner islands 



6. T. grayii Charles, Gardner, Champion, 



and Enderby islands 



7. T. alhemarlensis barringtonensis Barrington Island 



8. T. albemarlensis Indefatigable, S. Sej^mour, N. 



Se3-mour, Daphne, James, 

 Jervis, Cowley. Brattle, Albe- 

 marle, and Narborough is- 

 lands 



Origin of the Galapagos Lizards of the Genus 

 Tropidurus 



The genus Tropidurus, 2.5 at present understood, is confined to 

 the Galapagos Archipelago and South America. It has been re- 

 ported from Paraguay, iVrgentine, Chile, Bolivia, Peru, Equa- 

 dor, Brazil, Dutch Guiana, and Venezuela. The closely allied 

 genus Leiocephaliis occurs in Bolivia, Peru, Equador, Colom- 

 bia, Brazil, the Greater and Lesser Antilles and the Bahamas. 

 It is evident, therefore, that the affinities of these Galapagos 

 lizards are South American and A¥est Indian. Either the 

 lizards of the Galapagos have been derived from South 

 America, or those of both localities have common ancestors. 



In the Galapagos Archipelago, Tropiduri occur on almost 

 every island, islet, and rock. The notable exceptions are Cul- 

 pepper, AA^enman, and Tower islands. They have been found 

 on Abingdon, Bindloe, Chatham, Hood, Gardner-near-Hood, 

 Charles, Enderby, Champion, Gardner-near-Charles, Barring- 

 ton, Indefatigable, North and South Seymour, Daphne, James, 

 Bartholomew, Jervis, Duncan, Cowley, Brattle, Albemarle, and 

 Narborough islands. 



The fact that these lizards occur on nearly every island of 

 the archipelago can be explained only in one of two ways. 

 These Tropiduri must have reached these islands either by 

 land or by w^ater. Either they have been carried to each 

 island, islet, and rock by some such means of dispersal as float- 

 ing driftwood driven by the winds and currents, or else they 

 were already on each island at the time when it became sep- 

 arated from a larger land-mass. The former view has been 

 held by those "who believe that these islands never have been 

 connected, but have been independently thrust above the sur- 

 face of the ocean. The latter explanation finds favor with 



