STUDIES IN MARINE ECOLOGY. 



235 



Other animals to be found here are: Natica duplicata, Nereis 

 virens, Polycirrus eximeus, burrowing in the mud ; Nassa obsoleta 

 and the hermit crab, P. longicarpus, with its commensals, 

 Hydractinia and Crepidula convexa, on the bottom, retreating as 

 the tide ebbs; and Ostrcea virginica growing occasionally on 

 the rocks. 



Table XII. 



Showing the Results of Analyses of the Water over the 

 Mya Association. 



The temperature of the water in this association runs much 

 higher than on the rocks; 28 degrees C. was recorded. The 

 exposed mud at low tide must run still higher. Few oxygen 

 tests were made here, but they showed, as was expected, that 

 there is a good supply of oxygen in the water. In the upper 

 reaches, at least, the water does not cover the mud long enough 

 to lose much of its supply which came in with the high tide. 

 Under low tide conditions the mud must contain almost no 

 oxygen at all. The pH may be markedly lower than on the 

 other associations, correlated with the fact that the muck is acid. 

 The observed salinity is the same as for the marginal muck 

 association but it probably runs lower on occasion, from the 

 drainage after rains. 



Table XIII. 



Showing the Temperature, Oxygen Tension, and pH of the 

 Melampus Association. 



