16 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 73 



Lignumvitae Key which are so close to graphicus that it would 

 puzzle an expert to tell them apart, but there were intermediates 

 between them and lignuTJivitae. While the porcellanous structure 

 is one of the chief characters of what we call solidus^ it is almost 

 absent in psetuiopictus, and the axial region in the species may vary 

 from almost dark purple to pure white. 



It may seem that I have recorded a large number of minor eleva- 

 tions and depressions, mere oscillations, in lower Florida since the 

 first appearance of the land, and I feel sure that there have been, 

 as for most of them there is still in existence evidence in the form 

 of raised beaches, eroded bluffs, or sunken forests, Samuel San- 

 ford corroborates this statement and says that in places they have 

 been rapid enough to be proved by human records.^ 



Almost all of lower Florida is very flat, and it rises but slightly above 

 sea level. The same authority I have just quoted remarks, on page 

 189 of this second report, that "A difference of 2 feet in water level 

 means the difference between shallow lake and dry land for hundreds 

 of square miles." So also in the immediate vicinity of the sea a sub- 

 sidence of less than a foot might mean mangrove swamp and a corre- 

 sponding elevation land covered with Ligims -hearing hammock. 



But the vertical movements were only slight from the first appear- 

 ance of land in this region until now. At no time has there been a 

 subsidence so gi'eat that the large lower island or the rocky mainland 

 has been drowned out nor an elevation sufficient to make dry land of 

 the bays along the southeast coast of the mainland, for in that case 

 the warm temperate flora of the rocky ridge would have crossed over 

 to the Upper Keys, and had there been a drown out the distribution 

 of our plants and Liguus would have been very different now from 

 what they are. Since the first great Pleistocene elevation I do not 

 believe that the change of level has amounted to 15 feet. 



The colonization of Liguus on the mainland of Florida came about 

 under quite different circumstances from those of Cuba or most of 

 our keys. In both of the latter areas there was a practically continu- 

 ous growth of tropical forest which was exactly fitted for a home for 

 these snails. They are hermaphrodites, and during their period of 

 activity it is probable that most of them copulate and become gravid. 

 A.t this time a considerable number of individuals come down from 

 the trees on which they make their homes, and instead of depositing 

 their eggs in the ground near them they obey a call to form a new 

 colony. They travel directly away, probabl}'^ going in a reasonably 

 straight direction, and whenever they are satisfied they stop, dig out 

 & shallow excavation among the leaves and trash, lay their eggs, 

 cover them, and find a near-by tree for a new home. There is no 



* Second Report Florida Geological Survey, p. ISO. 



