the percentages ranging from about 30 to 70%. 
476 
In Quiver Lake the 
principal part of the decrease resulted from a heavy falling off in the 
small Mollusca, the unusual numbers of dead snails found everywhere 
in the lake in 1915 seeming to point to some exceptional mortality from 
unexplained causes. 
- 
Bottom Fauna Stocks, LAKES IN VICINITY oF Havana, 1914 anp 1915, 
(JuLyY—OcToBER) 
Incr. or 
Pounds per|Pounds per 
acre, 1914’ | acre, 1915 decr. per Notes 
cent. 
Thompson Lake 310 496 +60% |No essential change in 
over 6 ft. &* 8 composition of fauna 
1—6 ft., 903 647 —28% si i 8 oe 
some vegetation 10 7 yeti 
1—6 ft., 501 296 —40% s ss s ff 
no vegetation 12 7 
Quiver Lake 2,805 803 —T1% e cf aS « 
over 6 ft. 15 3 
1—6 ft., 388 158 —59% |Great decrease in snails 
some vegetation Le, 14 and increase in Chiro- 
* The Italic figures give the number of collections. 
. 
nomidae between 1914 
and 1915 
te 
