CHAPTER XVI 



THe Story of tKe Land Snails 



THE land snails of Lower Florida, like 

 most of its animals and plants, form a 

 mixed assemblage of various origins. 

 A few minute species are derived from 

 the northern States; a considerable number pro- 

 bably migrated here from the Texas region, and 

 perhaps half of our fifty, species had their origin 

 in the American tropics. 



It has been generally held by biologists that 

 life originated in the sea, from which it spread to 

 the land; we have excellent support for this theory 

 in our own mollusks. Several of our Littorinidae, 

 marine gastropod mollusks with spiral shell, gills 

 and an "operculum" or lid that closes the aper- 

 ture, live, for the most part, on land near the sea. 

 One strictly gill breathing species (Littorina 

 angulifera) becomes actually arboreal on the man- 

 335 



