80 COMMUNITIES OF LARGE LAKES 
recorded below 9 meters and not on the open shores. All are found in 
small lakes and sluggish streams. 
d) Lower shore formation (8-25 meters) (Station 3; Tables XI, XIII, 
XV).—The belt immediately below the shore belt is characterized by 
wave-action sufficient to move only the finest material. Its lower limit 
is the limit of wave-action; the beginning of light diminution; the lower 
limit of daily fluctuation in temperature; and the lower limit for most 
of the species of Mollusca (75, appendix). Practically all the forms that 
have been recorded here are inhabitants of still, shallow water also. 
Notable among these are the common still-water amphipod Eucrangonyx 
gracilis, the little bivalve Sphaerium striatinum, and several species of 
Amunicola and Valvata which, together with Lymnaea woodruffi, are more 
characteristic of Lake Michigan than of shallow waters. While a large 
number of Mollusca are recorded from the lake above 25 meters only the 
Sphaeridae are found below this limit. Small annelids, midge larvae, 
and leeches are very abundant north of Gary, Ind., in 11 meters of water. 
This belt is the principal breeding-ground of the whitefish. The 
eggs are deposited on the bottom and left unguarded. It appears that 
the young fish stay in the shallow waters for a considerable time. Wher- 
ever the bottom is firm the lake trout breeds also. Nearly all the fish 
traps are set in the upper edge of this belt and in the lower boundary of 
the one above. 
e) Belt of overlapping: upper deep-water belt (25-54 meters) (Tables 
XIV, XV).—This belt is characterized as below wave-action, below 
daily fluctuations of temperature, with seasonal fluctuations not exceed- 
ing 3° C. It is intermediate between the belt above and the deep belt, 
and is the characteristic feeding-ground of the whitefish and the regular 
home of the long-jaw (Argyrosomus prognathus, Fig. 21). On the other 
hand, it is the upper limit for some of the deeper-water forms, such as the 
well-known Mysis relicta and Pontoporeia hoyi (Figs. 22, 23), the deep- 
water crustaceans which are the chief food of the whitefish. 
f) Deep-water formation (54 meters to bottom) (Table XV).—This 
belt is characterized by weak or no light and by seasonal changes in 
temperature less than 1 degree. Below 115 meters there are no light 
and no seasonal changes, and the temperature is 4° C. throughout the 
year. Off Racine in 82 meters (265 ft.) the bottom is of reddish-brown 
sandy mud (82); in g5—125 meters (311-410 ft.) dark-colored impalpable 
mud, depressions with decaying leaves (82a). In the Grand Traverse 
Bay region, Milner found decaying sawdust in 183 meters (600 ft.) (81). 
Except for unimportant variation in bottom, conditions are practically 
uniform throughout. Milner (81) states that the invertebrates are 
