XIV INTRODUCTION. 



or large size have often been spread by the accidental means 

 invoked to explain inter-island distribution, though we have 

 the strongest evidence that small or minute land snails have 

 spread, probably by hurricanes, over considerable distances. 

 The actual facts of distribution of Hawaiian Island snails do 

 not indicate, to my mind, a migration from Kauai. 



III. 



The logical geographic boundaries of most species of Achati- 

 nellidcF give excellent ground for the belief that the present 

 distribution of all the larger species has been attained by 

 their own means of locomotion, and that unusual or so-called 

 accidental carriage, as by birds, drifting trees, etc., has been 

 so rare as to be negligible. No evidence whatever of such 

 carriage is known to me. It is likely that Unionid glochidia, 

 Ancyli, or some other fresh- water mollusks may sometimes be 

 transported by water-fowl, but I know of no North American 

 land snail of moderate or large size, whose distribution re- 

 quires such a hypothesis, excepting Liguus and Hemitrochus 

 in Florida, which seem to have reached our shores without 

 land communication. These snails inhabit trees on the keys 

 of Florida wooded islets but a few feet above the seas, some- 

 times actually swept by the waves, so that their transporta- 

 tion on drifting trees, as advo'cated by Mr. C. T. Simpson 

 and others, seems possible, yet even in these cases the eggs 

 may have been carried by hurricanes. In the Hawaiian 

 Islands the AchatinellicUz inhabit mountain forests ; there are 

 no rivers to transport trees carrying snails to the sea. Even 

 if so transported, the 'chance is almost infinitely remote that 

 if cast up on another island the conditions on the shore would 

 be favorable for such snails. If the transportation of arbo- 

 real Achatinellidse by such means is improbable, that of large 

 terrestrial forms is even more difficult. It is hardly worth 

 while alluding to the possibility of these snails being trans- 

 ported by birds, since everybody having practical knowledge 

 of land snails understands the absurdity of such a proposition. 



As mentioned above, hurricanes have doubtless been in- 

 strumental in spreading minute species of land snails. If 



