20 



Nils Rosén 



with, the sea, the sahnity has gradualy increased, converting them to real salt ponds. 

 The fauna in them has originally invaded from the sea, when the pond was still in 

 connection with it, but under the peculiar conditions, under which these forms have 

 had to live, the water getting more salt, they have become somewhat modified. It 

 would be of a great interest to study this fauna and its modification, as all inter- 

 mediate states of ponds between bights, in broad connection with the sea, to thesee 

 salt ponds perfectly cut off are to be found. Unfortunately this has been done very 

 little. Some shells from a salt lagoon on Watlings have been collected, Dall ^ 

 having given a few notes on them: »The changes to which they were subjected 

 appear to have been an increase in the salinity and consequently in the specific 

 gravity of the water; higher temperature; and greater exposure to sunlight. All 

 the lagoon species as compared with their nearest alliest exhibited certain common 



differences ; these were te- 

 nuity of shell, diminutive 

 size, and intesifi cation of 

 colour when the species was 

 other than black or white » . 



(c) The Fauna in the Sea. 



No region of the fauna 

 in the Bahamas shows such 

 a variation as that of the 

 shore, a study of which will 

 be of some interest. There 

 are two different types of 

 shores, the rocky shore. 

 Fig. L. Creek on west side of Andres. consisting as mentioned 



above of coral sand cemen- 

 ted to limestone, and the sand-beach. The faunas of these two regions are rather 

 different, the former being by far the richest. 



The rockt/ shore fauna. When the shore slopes gently towards the sea, several 

 regions of the shore can be distinguished, according to the shape of the rock and 

 according to the extent to which it is covered by water at different tides. During 

 my visit to the Bahamas I had many opportunities of studying these different parts 

 of the shore and the fauna which is characteristic of each region. The conditions 

 that have caused this regional difference in the fauna are in all probability not 

 only the level of the sea but also the salinity and the temperature. The water 

 that remains in the holes, when the tide draws back, gets very warm (in summer 

 about -|- 32 " C.) and salt. I am here giving a few accounts thereof. 



' »Bahama Islands», ed. by Shattuck, pag. 45. 



