﻿DALL] shells COLLECTED IN THE BAHAMAS 447 



amined was about ten or fifteen feet across and about lour feet 

 deep. I found in it only one or two Physas but there were a great 

 many Planorbis. 1 was much puzzled as to whence they came, and 

 made a careful search to see if I could find any live ones. I ex- 

 amined the mud and looked in the very bottom where the mud was 

 still soft but could unearth none. Then I looked in the crab holes, 

 feeling round the sides and taking up handfulls of mud from the 

 sides and bottom and straining it through my net. I thought there 

 must be considerable numbers of live ones somewhere or there would 

 not be so many freshly dead ones, but could find no trace of any. 

 Later 1 discovered a pond where the natives shoot wild fowl in 

 winter, and called by them the " duck pond." Hereabouts the land 

 is nowhere more than eight or ten feet above high water mark, and 

 probably the water in this pond was in subterranean communication 

 with the sea, not more than a quarter of a mile away. The pond 

 was one hundred yards or more from where I found the Planorbis. 

 It was a natural pond, very shallow, but with a soft muddy bottom 

 over the lime rock, and all about it bushes and trees were thick. 

 The trees extended into the water, growing in it to a depth of two 

 feet. In the pond were some fresh water algae and other plants. I 

 thought I had found where my Planorbis came from, but on most 

 careful search I could not find one alive or dead, but did find a few 

 Physa, some of which were alive. The pond was the only one I 

 heard of, remote from the village, difficult of access and there was 

 no water about where anything in the shape of aquatic plants had 

 been imported. Therefore I think there is no possibility of the 

 Physa being imported. Probably the water was salt or at least 

 brackish near the bottom. There were a number of the lime sinks 

 which had been cleaned out to form " wells," and one or two deep 

 sinks which had water in them fresh enough to drink. In one of 

 these, two miles from the cluck pond and back of the village I 

 found one Physa." 



The explanation, as far as the planorbes are concerned, is that 

 they form epiphragms when the waters of the pool dry up and "re- 

 main in this condition alive but quiescent until the rains fill up the 

 pools again. Many of the specimens of P. rcdHcldi showed the 

 epiphragm, usually double, very clearly through the translucent 

 shell. I believe this habit has not before been recorded of Planorbis. 



I agree entirely with Mr. Bryant's conclusion that these fresh 

 water species are indigenous and native to the islands. There are 

 many ways by which such pools may be stocked. The greater pro- 

 fusion of specimens in the pools and their scarcity in the permanent 



