462 Wisconsin Academy of Sciences, Arts, and Lett rs. 
aquatic plants of this same area, that is, the region between the 
shore line and a depth of 7 meters, while another (no. XVIII) 
treats of the chemical composition of some of these plants. 
For purposes of comparison with the shallow water data, Mutt- 
kowski extended his studies in the spring of 1916 to the bottom 
fauna of the deeper water also, chiefly the region between 7 meters 
and 20 meters. The material from the deeper water was obtained 
by means of an Ekman dredge with which samples of the bottom 
could be readily secured at various depths, except in places where 
the bottom was composed of rock or pure sand. At the conclusion 
of Muttkowski’s investigation on September 1, 1916, the study of 
the bottom fauna of the deeper water was taken up by the present 
writer, and it was continued until the middle of August, 1918. The 
statistical data relating to the deep-water area which were obtained 
by Muttkowski between the latter part of May, 1916, and the first 
of September of that year, have been incorporated with those that 
were secured after the completion of his work. 
In September, 1916, an extended study of the bottom fauna of 
the deepest portion of the lake was begun. Five regular stations 
were established within the 20-meter area, and observations were 
made at these stations at frequent intervals, usually once a week, 
except when the lake was covered with ice; during the winter sea¬ 
son the stations were visited only once or twice a month, but in 
summer they were sometimes visited as often as twice a week. The 
stations were widely separated in order to secure a fair average 
for the whole area lying within the 20-meter contour line. The 
depth at the various stations varied from 20.5 meters at the shal¬ 
lowest station to 23.5 meters at the deepest one. The bottom at 
these points consists chiefly of marl, the upper part containing a 
fairly large admixture of organic material derived from the plank¬ 
ton as well as from the shallow water and shore vegetation. A 
certain amount of clay was found also, particularly at the two sta¬ 
tions situated in the western part of the lake. Chitinous material 
derived from the shells of the plankton Crustacea appeared in the 
upper layers of the mud. 
A sixth station was established in a depression toward the south¬ 
ern side of the lake where the water reaches a depth of 18.5 meters. 
At this point a somewhat larger proportion of vegetable debris was 
found in the mud as well as a slight admixture of sand. 
Observations were made, in the latter part of 1916, which ex¬ 
tended in series from shallow water to deep water, and such ob- 
