36 



later, a slightly soft and tenacit)iis bottom with a limited growth 

 oP vegetation apparently ofifers the best' conditions for them in 

 this region. 



The food of the clam is similar to that of the oyster and 

 scallop, namely, diatoms and other microscopic organisms, while 

 feeding a constant flow of water takes place through the mantle 

 chamber, the water entering through one siphon tube and pass- 

 ing out the other. As it circulates through this chamber it 

 bathes the surface of the body and gills, which are covered Avith 

 microscopic, thread-like cilia, which beat constantly in a given 

 direction. By their movements they aid in keeping up the cur- 

 rent of water and also carry the food particles, which come in 

 contact with them to the mouth. 



No very small clams were found alive at this time, and only 

 a few small shells were picked up on the shore at one point. 



It is also notable that on any particular bed the clams are 

 of nearly uniform size instead of being several different sizes, 

 as would be expected. For instance, at bed No. VIII. the clams are 

 all of approximate maximum size (six inches long), while on 

 several beds( especially 4 and 6) they are only about half that 

 size. It is very probable that a study of the conditions during 

 the breeding season w^ould give a clue to the reasons for this, 

 and might also make it possible to explain the limited number 

 of clams found on most of the beds, none of which are stocked 

 with anything like the numbers which they should support. 



v. ENEMIES. 



While numbers of dead shells of both forms have been 

 found scattered over the various beds, in most cases it has 

 been impossible to determine the destructive agent. Two species 

 of conch (FuJgur perversa and F. pyrum) are rather com- 

 mon on the flats, and several other small gastropods are also 

 abundant. Clams partly devoured by the larger species of conch 

 {F. perversa) have been found by the lighthouse keener, but 

 I have never seen them being destroyed. Numbers of 

 ciam shells have been found with the edge of one valve 

 chipped away, leaving a small hole, and it is possible that some 

 one of their enemies has attacked them in this manner. Sud- 



