438 
2. Borrom Fauna or LAKE MEnvora. (Murrxkowsk1, 1918) 
Average valuations in pounds per acre for the 0—1- and 1—3-meter 
zones obtained by Muttkowski in Lake Mendota in 1914 and 1915 (60 
and 64 Ibs. respectively) are slightly higher than our averages of 1916 
from the 1—6-foot zone of Fox and Pistakee lakes (54 lbs.), but are 
well under the average for the six isolated glacial lakes (105 lbs.). 
Mollusca formed only 4% of the total average weight in the 0—1-meter 
areas, and 14% in the 1—3-meter zone. The most important groups of 
animals as measured by weight were the larvae of Chironomidae and 
Trichoptera. 
BoTrtoM FAUNA OF LAKE MENDOTA, WISCONSIN. 1—3 METERS 
POUNDS PER ACRE (OUR VALUATIONS) 
Per cent. 
Mollusca | Others | Total roses 
0—1 meter | 2.59 | 57.37 | 60 | 4 
1—3 meters | 9.40 | 55.12 | 64 | 14 
3. Marine Botrom-Fauna. VaLuaTions, DENMARK 
(PETERSEN, 1911—1918) 
The marine bottom-fauna valuations, by rough weight, obtained by 
Petersen 1910 to 1916 included the shells of Mollusca and echinoderms, 
and require reduction by percentages that probably range at least 33 to 
75%. His average valuations for large areas all concern the bottom 
fauna outside the 6-meter limit, in depths ranging from 10 meters up- 
wards. The average valuation obtained for the Thisted Bredning, years 
1910—1916, with an area of 65,000,000 m.? (==16,055 acres) was 3,298 
Ibs. per acre, rough weight, which would figure down by. the percentages 
mentioned to 800 to 2,200. The Nissum Bredning averages for 110,- 
000,000 m2 (27,170 acres) was somewhat lower, 2,418 lbs., which would 
stand with deductions of 33 and 75% at 600 or 1,600 Ibs. 
Petersen’s figures for restricted Mytilus and Modiola (a mollusk re- 
lated to Mytilus) communities—167,556 and 92,036 Ibs. per acre, or 83 
and 46 tons, respectively, the first in 2-meters depth, the second in 28 
meters—by far exceed anything that has been reported elsewhere, so far 
as we know, for sea or land crops. The figures in the case of the Mytilus 
haul are equivalent to 552.9 ounces per square yard, or to 0.42 ounce 
per square inch of bottom area: and those for Modiola, to 303.7 ounces 
per square yard, or 0.23 ounce per square inch. These figures com- 
pare with about 10 ounces-per square yard (3,029 lbs. per acre), the net 
average weight* of the Illinois River channel collections of 1915 between 
* Shells of Mollusca deducted. 
