JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. io march 4, 1920 No. 5 



ZOOLOGY. — On the relations of the sectional groups of Bulimulus 

 of the subgenus Naesiotu Alters. William HealEy Dall, 

 U. S. National Museum. 



The Naesioti are developed in considerable profusion in the Gala- 

 pagos Islands. They are related to the small translucent ground 

 snails of the genus Bulimulus, which are common to the elevated 

 forest region of South America nearest to the islands and which 

 were probably transported originally to the Galapagos group by 

 high winds while attached in a state of hibernation to dead 

 leaves or similar light material. After reaching the islands their 

 opportunity for evolution into a variety of types was fostered by 

 isolation, differences of food supply and the modifications due 

 to volcanic dust from the disintegrating lavas. In a report to 

 the California Academy of Sciences on the species collected by 

 Mr. W. H. Ochsner of their Galapagos expedition, prepared in 

 191 6, but still unprinted, their relation to situs, distribution 

 among the islands, and apparent protective modifications are 

 discussed at length, and in 1896^ some of the probable causes of 

 the peculiarities developed in such insular faunas were considered. 

 Nothing in the landshell fauna lends weight to the hypothesis 

 that these islands were ever connected by land with the continent 

 of South America. The Tertiary fossils obtained by the Cal- 



^ Insular landshell faunas especially as illustrated by the data obtained by Dr. 

 G. Baur in the Galapagos Islands. Proc. Acad. Nat. Sci. Phila. August, 1896, pp. 

 395 to 459, pi. 15-17. Also supplementary data in the same periodical for 1900, 

 pp. 88-96, pi. 8. 



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