MUSSEL FAUNA OF THE KANKAKEE BASIN. 



15 



bed from Ober to where it empties into the Kankakee, all of Avhich 

 has been artificially dredged. The dredged portion begins 1 mile 

 west of Ober, and since the sole aim of the contractors was to cover 

 the greatest possible distance at the least expense, irrespective of 

 natural scenery, animal and vegetable life in the river, or in fact any- 

 thing else, they did not follow the old winding channel, but cut across 

 country in a straight line, which intersected the old bed at various 

 places. This dredged part is of nearly uniform depth, from 1 to 3 

 feet, with a flat bottom of sand and gravel, which the swift current 

 washes up into ripple marks, zigzagging across the entire w^idth of 

 the river. The current is uniform from 4^ to 6 miles an hour and 

 keeps the finer sediment in constant motion along the bottom, thus 

 forming an effectual barrier againt mussel life. Hence, although 

 this stretch has been dredged eight years, and there was an abundant 

 mussel fauna in the old channel, which was not killed off except in 

 limited areas, and which might easily have established itself in a 

 much shorter time in the new channel if the conditions had been 

 favorable, practically no progress has been made in that direction. 



An occasional L. ventricosiis ^vas found alive in the dredged chan- 

 nel, together with shells of Q. ruhiginosa^ L. irisj L. Ugramenfinus^ L. 

 luteolus^ etc., which had recently died (probably washed in from the 

 old channel). 



No real restocking can be expected until the bottom gets thor- 

 oughly solidified, packed down so that it will not wash along con- 

 tinually, and until at least some breaks in the current are formed 

 similar to those in the old channel. 



All the mussels found in this long stretch of 20 miles were ob- 

 tained from the old channel, and it was very interesting to see how 

 completely they had accommodated themselves to the changed condi- 

 tions. Instead of a good current running over a sandy or gravelly 

 bottom and keeping everything clear and clean, we now find lagoons 

 and bayous in which the water is practically motionless except during 

 floods. 



Consequently, they are rich in algae and other water plants, and 

 the firm bottom has been covered with soft mud and in many places 

 with fine ooze, 2 feet or more in depth. And yet the mussels have 

 remained, Q. pustulosa being the only one killed off to any extent. 

 The others have succeeded in climbing up on top of the mud and 

 ooze as fast as it was deposited. Even the large and heavy rectus^ 

 ventricosus, and undulata are found on the very top. Hoav such an 

 unwieldly bulk as a full grown undulata can move about and actu- 

 ally lift itself up through mud so soft that it will not hold up an 

 empty shell is difficult to understand. But the undoubted fact re- 

 I mains that they actually accomplish it. A noticeable peculiarity of 

 all these lagoon mussels w^as the presence of a large tuft of growing 

 21432°— 12 2 



