Mr Logan oh tlie Habits of Testaceous Mollusca. 51 



whole of the islands are without either stagnant or running 

 water, yet there is a plentiful supply of fresh water for the 

 inhabitants, as well as for shipping. The springs which sup- 

 ply it issue from below the shelving or perpendicular rocks, 

 some of which are about high- water mark, and many of them 

 considerably below it, so that in some places fresh water can- 

 not be obtained till half ebb. Many of the animals above 

 mentioned were found so far up amongst the rocks and crags, 

 that two weeks would be required, even at a good snail's pace, 

 to enable them to reach the water ; and if they did venture 

 in, the first sea would dash them to pieces amongst the rocks. 

 More has been said upon this subject than some may think 

 necessai-y ; but error, when propagated by a man like La- 

 marck, ought not to be slightly passed over, as it becomes 

 doubly dangerous. 



At the end of March and beginning of April, three months 

 after the above remarks were made, in the entrance of the 

 Rio Nunios, I found upon the roots, trunks, branches, aiul 

 leaves of many of the mangrove trees, a subspecies of the La- 

 marckian genus Phasianella in great numbers. They are fur- 

 nished with a coriaceous operculum, and breathe only water. 

 Those found upon the trunks and roots below high-water 

 mark, ^vere not adhering to the tree more firmly than our 

 Turbo litioreus, and like it, when pulled off, the animals made 

 a sudden retreat into then- shell, at the same time discharging 

 the greater part of the Avater contained in their bronchia?. 

 But those on the branches and leaves of the trees above high- 

 water mark, were found adhering much more firmly; they 

 were also observed to discharge much less water from the 

 In-onchia-, — some of them very little, others almost none, re- 

 quiring considerable pressure with the finger to make it at all 

 perceptible. This led me into a more minute examination, and 

 I soon found that the greater part of tliose on the leaves and 

 branches above high-water mark, were completely glued to 

 the bark of the trees or leaves by a sort of white shining gum 

 or mucus, so as not only to exclude insects, but also the atmo- 

 spheric air. Many of them adhered so firmly, that the lip of 

 the shell would break off and remain adhering to the tree or 

 leaf, and in all cases a crackling or tearing noise was made ou 



