GALAPAGOS MOLLUSKS 307 



couple are probably common to the islands and the main- 

 land. All the others are restricted and quite peculiar to the 

 Galapagos archipelago.* 



The genus Bulimulus, to which most of the Galapagos snails 

 belong, comprises mostly species with ovate large heavy shells, 

 which would seem to be peculiarly unfit for accidental trans- 

 port by marine currents, though many live almost habitually 

 on shrubs. As defined by Dr. Pilsbry, the genus is restricted, 

 as I have already indicated, to the western borders of South 

 and Central America and beyond the latter as far north as 

 Mexico and Lower California. Eastward it passes along the 

 northern States of South America to Brazil, it extends to the 

 Antilles, and from Mexico to the southern United States. 

 Thus it is limited to North, South and Central America, the 

 West Indies and Galapagos islands. The Melanesian genera 

 Liparus and Placostylus are closely related. The range of the 

 large family Bulimulidae is very similar, one group being con- 

 fined to America, the other to the opposite side of the Pacific, 

 from Tasmania in the south through Australia to China north- 

 ward, and eastward to the Society islands. One is almost 

 tempted to invoke a Pacific continent in explanation of this 

 curious discontinuous distribution. It seems as if the family 

 had originated in some central Pacific area and had taken 

 refuge on the nearest lands east and west on the disappear- 

 ance of its ancient habitat. But we need not consider this 

 problem at present. 



There are three groups of apparently very closely related 

 Bulimuli in Chile and Peru, in the Galapagos islands and in 

 Lower California. The shell in these groups certainly is very 

 similar, being narrow and elongated, and possessing the same 

 texture. All the same, Dr. Pilsbry f is of opinion that this 

 similarity in appearance is not to be looked upon as indicating 

 close relationship, but as a case of convergence produced by 

 similar environments. He recognises three sections of Buli- 

 mulus according to the sculpture of the apical whorls of the 

 shell. The first of these lives in Argentina, Chile, Peru and 

 Bolivia, the second in tropical America, the Galapagos islands 



* Ball, W. H., "Insular Land-shell Faunas : Additions." 

 t Pilsbry, H. A., "Manual of Conchology," (Pulmonata), X., p. 127, 



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