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), 

 thebluegill, 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 debris; 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 debris. Associated with the fish are occasional musk turtles (Aro- 

 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. 



Fig. 70. — The case of a caddis-worm {M ol- 

 anna sp.), sandy bottom (Fox Lake, 111.) 

 (original). 



Fig. 71. — The same from below. 



