346 



most abundant in the two upper cross-sections, opposite Chillicothe 

 and Rome, at the latter of which the dissolved oxygen one foot above 

 bottom was under one part per million at stations embracing over a 

 mile of lake-width early in August. The species was also taken, how- 

 ever, at a large proportion of the stations in the upper part of the 

 middle lake and at a few in the lower. 



The undescribed species of Limnodriliis had a distribution in the 

 summer of 1922 very much like that of L. hoffiiieisteri, be'ing taken at 

 nineteen out of the twenty-three upper lake stations, embracing three 

 cross-sections ; and was also taken in scattered hauls both In the middle 

 and the lower lake. Tuhifcx tubifex, on the other hand, was taken in 

 or just above the upper lake in 1922 only in the Chillicothe and Rome 

 cross-sections, where it occurred at only six out of twelve stations ; 

 was not recorded at all from the eleven stations in the Spring Bay 

 cross-section ; and was recorded only once each from the middle and 

 lower lakes. 



The distinct tendency toward confinement of Tubifex tuhifcx, as 

 here understood, to the Chillicothe and Roman cross-sections may be 

 accepted as further confirmation of the value of that species as an indi- 

 cator of bad bottom ; though it is believed that the facts of outside 

 distribution before mentioned suggest that great caution be used before 

 basing conclusions as to the cleanness of muds upon mere occurrence, 

 either of this or other species. 



When the totals of all Tubificidae are tabulated, it is suggested 

 that numbers may be quite as important as specific identity when we 

 are seeking an index of the condition of the bottom muds in the small 

 annelids. Averaging 22,400 at Chillicothe, and averaging 29,000 and 

 ranging as high as 69,000 opposite Rome in early August, 1922, the 

 total of all worms dropped to only 2,100 per square yard in the next 

 2.4 miles (cross-section 1.5 miles above Spring Bay) ; and to a figure 

 of only 420 per square yard in the first cross-section in the middle 

 lake, another 4.5 miles south. The sharp decline in the 2.4 miles be- 

 tween Rome and the next cross-section southward corresponded to a 

 rise of less than two parts per million in the bottom dissolved oxygen 

 on the round of August 9, 1922, and was proportionately more eni- 

 frtiatic than the oxygen figures in suggesting the rapidity of improve- 

 ment in the water and the muds after they spread out into the upper 

 lake wide-waters just above Rome. 



