234 W. C. ALLEE. 



Except for salinity, the water over the marginal muck associa- 

 tion shows much less range in variation than in the 5. acutus 

 association. Thus the recorded temperature range is n° C. 

 against 15 ; the pH range, 0.8 vs. 1.7; the oxygen, 5.24 c.c. per 

 liter against 12.97. These are the natural results of the lack of 

 green plants in this association. On the other hand a careful 

 (laboratory) determination of salinity, made just after a heavy 

 shower that was one of a series running through a whole morning, 

 showed the effects of fresh water drainage from a nearby swale 

 by recording a salinity of 2.22 per cent. It is probable that this 

 lessened density extended into typical Scoloplos acutus territory, 

 though in a less marked form, but no tests have been made there 

 under these conditions. Dilution after a really heavy rain would 

 be much greater. The results from analyses of water over the 

 Thy one beds are shown in Table XI. 



/. The Intertidal Associations. — In this area the flats extend 

 back to old shore lines where the rocks characteristic of shores 

 are being gradually covered by mud accumulations; these are 

 the typical mud flats which I have been describing. These 

 margins, rising more or less steeply from the water, are the home 

 of the intertidal associations. Most obviously there are two of 

 these : that of the animals near the low tide level, and that near 

 high tide. The former is dominated by Mya and is best under- 

 stood if called the marginal Mya association; the latter associa- 

 tion depends on location for its typical animals. That most 

 studied has been the Melampus association. 



(1) The Mya Association. — In the localities studied for this 

 report, the Mya association is best represented along the west 

 shore of Northwest Gutter Flats. The rocks there are an 

 extension of those of the exposed rock association, but since they 

 are located in the back part of the flats, mud has been deposited 

 around them until in many places they are almost entirely 

 covered up to the mid-tidal region. Here from well below low 

 tide to about mid-tide the siphons of small Mya 1 are so numerous 

 as to appear like stippled spots against the mud background. 

 In the lower part, the larger siphons of Venus give variety to 

 the stippling. If one try to dig up the clams, he encounters the 

 buried rocks within a few inches of surface. 



1 Mr. G. M. Gray informs me that he has never taken Mya in pure muck. 



