MUSSEL FAUNA OF THE KANKAKEE BASIN. 21 



foot of the mud. These mussels also usually had a large mass of 

 alga? attached to their upper ends and forming a sort of fumiel in 

 the water. "VVliatever may be the effect of the supporting power 

 of the algse in the mud, the two furnish a good example of sym- 

 biosis. The mussel supplies the alga with a place of attachment, 

 otherwise lacking, and in return the alga helps to purify and 

 oxygenate the water for the mussel. 



Q. undidata was by far the most common species, there being two 

 of them to every one of all the other kinds. No adult Atax jjarasites 

 were found in this species, but the mantles of many of them con- 

 tained clusters of the eggs. 



Each of the Q. imstulosa (75 specimens in all) contained from 

 several to a large number of adult Atax^ besides clusters of eggs in 

 the mantle, and young in various stages of development, swarming 

 over the gills. Q. coccinea contained no parasites at all, and the 

 nacre of all but two of them was white and would make excellent 

 buttons. L. ventricosus had an abundance of young Atax in the 

 mantle and on the gills, and many of them had dorsal baroques. 



L. rectus showed anywhere from 10 to 20 adult Atax in each speci- 

 men, besides plenty of young and an occasional Cotylaspis. A mar- 

 ginal baroque was found in one, and the nacre of all was a deep 

 purple. None of the other species contained parasites. 



Station 15. Kankakee River at the crossing of the Nickel Plate 

 Railroad. — Just above the railroad bridge is a large island with the 

 old channel to the west of it and the newly dredged one to the east. 

 The water runs through this old channel oftener than at the previous 

 station, so that only a few inches of mud have been deposited. The 

 mussels were very abundant here, forming the largest and most 

 densely populated bed found anywhere in the old channel of either 

 river. There was much driftwood buried in the mud along the west 

 bank of this old channel, and the mussels were clustered around the 

 twigs and branches as thickly as they could stand, seeming to get 

 some support from these solid objects. 



Farther up behind the island the water was shallower and there 

 was a perceptible current and no mud. Here the mussels were 

 actively moving about, and as the water was clear they could readily 

 be found. 



On examination, none but the Q. pustidosa contained any parasites, 

 but these had enough to compensate for any lack in the others. 

 Every specimen was infested, and it was not at all uncommon to 

 find 50 or 60 adult Atax, besides the eggs and young, in a single 

 mussel. Many of these mussels contained small pearls and some of 

 them dorsal baroques. 



The Q. coccinea, again, had white nacre, none of the rosy nacred 

 being found, and being at the same time large and flat, furnished 

 9275°— 13 12 



