Chilton. — Note on a Water-beetle found in ISea-ivater. 63 



Art. XII. — Note on a Water-beetle found in Sea-water. 



By Charles Chilton, M.A., D.Sc, F.L.S., Professor of 

 Biology at Canterbury College. 



[Read before the Philosophical Institute of Canterbury, 7th June. 1905.] 



In January, 1905, while searching in the rock-pools at Island 

 Bay, Wellington, for marine animals, I found a water-beetle 

 swimming freely among the seaweed in one of the pools. 

 Only the one specimen was seen, but it seemed quite at home, 

 and was behaving just as it might have done in fresh water. 

 As its occurrence in salt water appeared rather unusual, 

 the specimen was forwarded to Dr. David Sharp, of Cam- 

 bridge, England. 



He informs me that it is Bhantus pulvtrosus, Stephens, 

 a species already known from New Zealand and elsewhere, 

 and that, as it is sometimes found in brackish ditches and 

 streams near the sea, there is a probability that it had been 

 passively carried out to sea by a flood ; a r . the same time 

 he points out that the distribution of this and of some other 

 species can only be explained by supposing that they are 

 capable of living in the ocean for a time, and, if a suitable 

 object presents itself to give them a starting-point, of taking 

 fresh flights from time to time. 



There is a small stream at Island Bay which opens into 

 the sea not very far from the place where the beetle was 

 captured, and it is quite likely that it may have been carried 

 into the sea from the stream during a flood ; but even if it is so 

 the beetle must be capable of living for some time in actual 

 sea-water, for the pool in which it was taken was freely 

 exposed to the inflow of the waves at all times except at dead 

 low tide, and the stream was at such a distance and the 

 volume of water in it so very inconsiderable that it could 

 make no appreciable effect on the salinity of the water in the 

 rock-pools. 



Darwin in his " Voyage of the ' Beagle ' records the 

 finding of several live water-beetles swimming in the ocean 

 seventeen miles from land, off Cape Corrientes, and considers 

 that they had been floated into the sea from a small stream 

 which drains a lake near the cane. He also records the find- 

 ing of a species of Hydrophilus in a lagoon near Eio Janeiro in 

 which the water was only a little less salt than in the sea. 



I have thought it worth while to record the above facts, for 

 exceptional occurrences of this kind are often of special 

 value in the explanation of difficult questions that may arise 

 in connection with geographical distribution. 



