353 



A third species of Pisidium, close to P. complanatiiin Sterki, was 

 taken twice in the summer of 1922 in the far east wide-waters of the 

 upper lake, once in the Rome and once in the Spring Bay cross-r.ection. 

 Tubificidae exceeded 6,000 per square yard at one of these stations 

 and especially bad odors were recorded at both. 



It may be mentioned here that Miss Emmeline Moore (informa- 

 tion by correspondence) found Pisidium compressum and also an un- 

 named species near P. abditnin Haldcman in waters of the Skaneateles 

 outlet, New York, recently, under conditions that suggested a high 

 degree of tolerance. It is also of interest in the present connection 

 to recall that Juday (1908) took a species of this genus (P. idahoensc 

 Roper) in the deeper waters of the glacial lakes of Wisconsin, at 

 depths where for more than two months in the year there •\vas nearly 

 if not complete oxygen exhaustion. These specimens were found to 

 be quiescent under those conditions, but to revive upon being placed 

 in well-aerated water. 



Belonging to a group of snails and other botlo.ni species still less 

 tolerant than the Pisidia, is the little Valvata tricarinala Say, which we 

 took in small numbers in August 1932 about a hundred feet from the 

 west bank opposite Spring Bay. Here there was somewhat solider 

 bottom than farther out in the lake, though no vegetation ; and no 

 especially bad odor was recorded. As this species is more frequently 

 than not a shore form and more than ordinarily partial to vegetation, 

 the question of the amount of tolerance possessed by it does not affect 

 any conclusions already or later drawn as to the condition of the bottom 

 nnids of the great portion of upper Peoria Lake. 



Middle Peoria Lake, Mossville to Al Fresco Park 

 (Mile 154.9—159.3 below Lake Michigan) 



Hydrography 



The three bottom fauna cross-sections through the middle lake in 

 the summer of 1922 began at Mossville, 3.2 miles below the last sec- 

 tion in the upper lake, and were approximately two miles apart in all 

 cases. The one at Mossville was 8.4 miles below Chillicothe, the one 

 at the foot of Horshor Island 10.9 miles below, and the one opposite 

 Al Fresco Park 12.8 miles below the first cross-section taken in 1922. 

 The width of Peoria Lake at Mossville in August 1922 was around 

 4,500 feet ; but had rapidly expanded to al)out 7,000 opposite the foot 



