126 COMMUNITIES OF SMALL LAKES 
belong to different families, but have similar cases and similar habits. 
This is a good example of what is meant by mores. The forms are very 
different, but their mores are similar. The Johnny darter, the straw- 
colored minnow (Fig. 72), and the blunt-nosed minnow are usually 
found (105) in the shallowest water. The Johnny darter, the blunt- 
nosed minnow, the miller’s thumb, and probably other minnows breed 
in these situations (105, 106). Crayfish are common here (in Wolf Lake, 
Cambarus virilis). 
Snails (such as Pleurocera subulare [Fig. 73], and sometimes Goniobasis 
livescens) are common on the shoals, crawling over the bottom which is 
always covered with diatoms, desmids, etc. These algae serve as food 
for the mussels. Miss Nichols 
found 16 species of algae on the 
shell of a specimen of Pleurocera 
taken from a Wolf Lake shoal. 
In the deeper waters (3 ft.) we 
find the same crayfishes and the 
same snails fewer in number 
than in the shallower parts of 
the shoals. Associated with 
them are the mussels (especially 
Lampsilis luteola, Anodonta mar- 
ginata and grandis). Such sandy 
and gravelly bottomed shoals in 
1-3 ft. of water are especially 
important to the food fishes. 
There are many first-class food 
fishes in all such lakes. Of 
those in Wolf Lake seven breed 
in these shallows. There are the large-mouthed black bass (Fig. 74), 
the bluegill, the pumpkinseed, the green sunfish, the perch (Fig. 75), the 
speckled catfish, and the crappie. Nearly all in making their nests 
scrape the bottom clear of all débris; the males guard the nests. The 
number of food fishes in a lake is related to the area of such shoals, which 
are accordingly of great economic importance and should be protected 
from destruction by the encroachment of vegetation and accumulation 
of débris. Associated with the fish are occasional musk turtles (Avro- 
mochelys odorata). Shoals are invaded by bulrushes and bare bottom 
may exist between them. Here the viviparous snail (Vivipara contec- 
toides) (Fig. 76) sometimes occurs. 
Fic. 70.—The case of a caddis-worm (Mol- 
anna sp.), sandy bottom (Fox Lake, IIL.) 
(original). 
Fic. 71.—The same from below. 
