AET. 20 FLORIDA TREE SNAILS SIMPSON 5 



lot of over 30 active Ligvms into a vessel of water, weighting them 

 down with a piece of board so that all were kept completely sub- 

 merged for 30 consecutive hours, and when released every one of 

 them crawled away as though nothing had happened. All were 

 clinging to the board when they were taken out. 



During the rainy season the wind in the Florida Strait blows for 

 the most part from the southeast, and this drives any drifting mate- 

 rial diagonally across the current toward the Florida Keys and 

 the southeast mainland. A slight, irregular flow of water takes 

 place along this part of the mainland and the keys in a direction 

 opposite to that taken by the Gulf Stream. This slow movement 

 keeps close in to the shore and would tend to carry drift to the 

 south and west, even in some cases that which had passed for a 

 considerable distance along the main current, thus helping to dis- 

 tribute material carrying Liguus along our southeastern shores. 

 The greater part of the cold Labrador current goes under the Gulf 

 Stream above Miami, and it is mixed up in this vicinity, so that it 

 sometimes drifts to the north and again to the south. It is quite 

 probable that the feeble current running westerly among the keys 

 is the last vestige of this cold river. 



Nearly all the inner shore line of the keys and the southeastern 

 mainland of Florida is fringed with a growth of mangroves, but 

 on the side fronting the open sea there are sandy or rocky beaches. 

 The trees growing in " the mangrove " usually stand in mud or very 

 shallow water ; and wherever they grow conditions are not favorable 

 for the landing of tree snails because, so far as I have been able to 

 observe, they never crawl over wet mud. However, during Septem- 

 ber, October, and November we have unusually high tides all along 

 our lower coast, then they sometimes reach an elevation of 2 or more 

 feet above the ordinary tide. In many cases Ligutis inhabit dead 

 trees or limbs, and such might easily be broken up during their 

 journey down the Cuban streams or while making the sea crossing 

 before reaching Florida. I have no doubt that in some cases these 

 snails reach our shores on comparatively small pieces of floating 

 timber, and these could easily drift in among the mangrove roots, 

 where they are not too crowded, during excessively high tides and 

 be landed on what is ordinarily high and dry groimd. If such a 

 landing happens to be made in the edge of a hammock, the snails 

 could crawl off and become denizens of the United States without 

 any formality. Of course, during hurricanes the sea may be driven 

 over the highest land on our lower coast, and it is most likely that 

 the greater part of the Ligtius have been landed and established in 

 Florida during such storms. At one time, since I resided here, the 

 wind during one of these storms drove the sea entirely over Elliotts 

 and Largo Keys and far out on the mainland of Dade County. 



