Juday—Quantitative Studies of Fauna in Lake Mendota. 483 
Protentlfies choreus. The larvae of Protenthes are like those of 
Chironomns in that they show a distinct preference for the inter¬ 
mediate depths; the average number for this zone is about 30 per 
cent, larger than that for the deep-water zone. 
In addition to the above mentioned forms, which constitute the 
regular macroscopic bottom fauna of the deep water, several others 
are found in the intermediate region, more especially in the 8- -IO¬ 
meter area. Leeches were noted in four samples from this zone, 
but the number was too small to be of any great importance in the 
general population of this area. Also some specimens of Hyalella 
were found in two samples obtained at a depth of 15 meters. 
Aquatic snails were noted in 22 samples taken from the inter¬ 
mediate depths, that is, in about 10 per cent, of the samples from 
this zone. With very few exceptions they were not found beyond 
a depth of 10 meters, but four specimens of Lymnaea were noted 
in one sample from a depth of 15 meters. One sample from a depth 
of 8 meters yielded 1,100 snails per square meter, but the average 
for the other 21 samples in which snails were found was 50 in¬ 
dividuals per square meter. Beyond a depth of 10 meters, snails 
constitute a very unimportant element of the population, from the 
numerical standpoint. 
Some larvae of Chironomus lobiferous were noted in four catches 
from the 8--10-meter area, but they were not found at greater 
depths. 
Larvae of Palpomyia longipennis were present in 13 samples 
from the intermediate zone, but the average number for these sam¬ 
ples was only 30 individuals per square meter. A specimen was 
found in one sample taken at a depth of 18.5 meters, but these 
larvae were obtained most frequently between 8 meters and 12 me¬ 
ters. 
Larvae of Sialis infumata were found in 28 samples from the 
intermediate zone. They were obtained at all depths in this region, 
but they were not noted in any of the catches made at a greater 
depth than 20 meters. The average number found in the 28 sam¬ 
ples amounted to 72 individuals per square meter, or about 10 per 
square meter on the basis of the total number of samples taken from 
the intermediate zone. Muttkowski (4) found them in the littoral 
zone only in the 5-—7-meter area, and his average for this area is 
approximately five individuals per square meter, or half the num¬ 
ber for the entire intermediate zone. 
