332 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



nental mass with which the Galapagos were connected or of 

 which they formed a part. 



When the Galapagos finally became separated from the rest 

 of the world, it is probable that most or all of the present 

 islands remained for a time united. The northern islands 

 must have been the first to establish an independent existence, 

 and it is possible that their separation may have occurred 

 before snakes reached the Galapagos, and, therefore, before 

 the old continental bridge was broken; but I think it more 

 probable that snakes once inhabited these islands also. Cul- 

 pepper and Wenman islands are, of course, unfavorable for 

 the continued existence of snakes. Just why they never have 

 been found on Abingdon and Bindloe is indeed hard to under- 

 stand. 



While all of the snakes of the Galapagos Archipelago are 

 closely related, they nevertheless are of two distinct types. 

 These are the small snakes with no scale-pits and fewer than 

 one hundred and ninety gastrosteges, and the group of species 

 with more than two hundred gastrosteges. 



These two groups I believe to be the descendants of. two 

 species which originally occupied the Galapagos. My chief 

 reasons for this opinion are the absolute distinctness of the 

 two groups, and the fact that representatives of both have 

 been found upon the same islands. 



The snakes with more than two hundred gastrosteges fall 

 naturally into three subgroups. These are: first, the snakes 

 of Charles and Hood ; second, those of Narborough, Albemarle 

 and Brattle; third, those of James, Jervis, Indefatigable and 

 Barrington. 



The first of these subgroups is the most distinct. Differenti- 

 ation has progressed much farther on Charles and Hood 

 islands than elsewhere in the archipelago. Therefore, we may 

 believe that these southern islands were separated from the 

 central ones before the latter were divided one from another. 



The snakes from Charles and. Hood islands are very closely 

 allied. They agree in all essential characters except color. 

 They alone of the larger Galapagos snakes lack the scale-pits, 

 and both have the same number of gastrosteges. Dififerenti- 

 ation could hardly have occurred along lines so absolutely 

 parallel in two unconnected islands. We are therefore led 



