FAUNA OF THE FLOTSAM 75 



a distance of over 400 miles in a south-easterly direction, 

 the bottom of the Bay of Bengal is an almost perfectly 

 level plain, lying between 1654 and 1676 fathoms below 

 the sea-level, having a temperature about two and a half 

 degrees above freezing-point on the Fahrenheit scale, 

 and consisting in more than 300 miles of its extent of 

 almost pure Globigerina-ooze. 



Whenever the ship lay-to to sound we had a haul 

 of the tow-net, and whenever a drift-log was sighted a 

 boat was sent away to have a look at it. 



These drift-logs are of great interest as being agents 

 in the dispersal of animals, both marine and terrene. 

 What we almost always found on them, besides a 

 crust of barnacles, were two species of grapsoid crabs, 

 one a swimming species named Varuna literata, the 

 other a rock species named Plagusia depressa. Both 

 these crabs are found in warm latitudes, over the 

 whole extent of the Indo-Pacific shore, and there can 

 be little doubt that their singularly wide range results 

 from their habit of clinging to ships and to timber 

 that gets washed into the stream of the great oceanic 

 currents. It was usual to find shoals of file-fishes 

 hovering round these drift-logs, but with what intent 

 we could not discover, for the stomach of one that we 

 caught and opened was full, not of barnacles, but of 

 the free-swimming oceanic mollusks known as sea- 

 butterflies {Pteropoda). 



I took particular notice of the extraordinary colour 



