236 W. C. ALLEE. 



(2) High Mud Shores {Melampus) Association. — The last type 

 of habitat in the series comes with the further deposition of 

 organic mud. Under these conditions the My a association would 

 gradually be raised above low tide level and finally above mid 

 tide level. Marsh grasses would come in and in place of the 

 association dominated by My a there would be one dominated in 

 places by the fiddler crabs (Uca) and in others by the snail 

 Melampus lineatus. The situations studied have had more of the 

 latter than the former. 



The Melampus grounds are well illustrated in the Uncatena 

 shore of Northwest Gutter from near the bridge to the gravel 

 spit marking the eastern side of the passage to the Bay and at 

 various places along the other gutter creeks, especially near the 

 rockweed association already located. 



The substratum is a peaty mixture of muck and roots which 

 is covered only at high tide and then by only a few inches to a 

 foot or so of water. In the lower parts the mussel Modiolus 

 demissus is present sometimes in abundance. At the upper side 

 the land insects, such as the carabid beetles, are plentiful, while 

 Thysanura are abundant over much of the region at low tide. 

 The ground is moist at all times on account of the spongy char- 

 acter of the substratum and the protection furnished by marsh 

 grasses. 



Too few analyses of water of this region have been made but 

 the low pH and accompanying low oxygen content of the water 

 as it leaves the flat when the tide ebbs, is significant. When 

 this water flows over the Melampus grounds, it would have a 

 pH of about 8.0 and an oxygen tension of some 4.00 c.c. per L. 

 The locality most studied would be covered with water about 

 six hours of the twenty-four. The salinity must vary from about 

 3.00 per cent, at high tide to practically fresh water when low 

 tide coincides with a heavy rain. 



IV. Summary of Data. 



There are two types of data which one desires concerning the 

 environmental complex of animals: First, what are the average 

 conditions during the period when the divisions between habitats 

 are most, pronounced? And second, what extremes are to be 



