74 THE EEPTILES OF THE GALAI'AGOS ISLANDS. 



America. The other five, Testudo, Tropidurus, Phyl- 

 iodactylus, Gonatodes, and Orophis, are genera of which 

 very closely allied species are distrilmted along the same 

 coasts. 



Only one of the species discovered on the islands, 

 Phyllodadylus tubercidosus, has not been distinguished 

 from those of the continent. It ranges from Chile to Cali- 

 fornia. The tnbercles of Dr. Baur's specimen differ so 

 much from those of the mainland form that the type may 

 prove to be a new variety if not a distinct species. The 

 balance of the species, though in cases but little differen- 

 tiated, are sufficiently distinct for recognition among their 

 continental allies. 



The affinities and the amount of differentiation of the 

 species on the various islands prove beyond question that 

 the insular genera and species were derived from those of 

 the nearest South American coasts, either somewhat di- 

 rectly and recently or more remotely, from common an- 

 cestors. While there is a general agreement in regard to 

 the sources from which the different forms of plants and 

 animals at present inhabiting the islands were primarily 

 derived, the agreement is not extended to the manner of 

 derivation. Advocates of the theory of independent, vol- 

 canic, origin of the archipelago claim that accidental intro- 

 ductions have established the flora and fauna, and explain 

 the varying affinities of the types by asserting the trans- 

 portation of the same or of different species to particular 

 islands and by the effects of isolation and varied surround- 

 ings. They do not consider the six hundred miles or more 

 of distance from the source of supply to be an insurmount- 

 able obstacle, and they are favored by the great Peruvian 

 current and by the winds. Advocates of another theory 

 hold that the islands once were mountains connected with 

 what is now the continent by lower lands, that by subsi- 



