128 COMMUNITIES OF SMALL LAKES 
Characters of the formation: The formation is distinctly dependent 
upon a clean bottom of sand or coarser materials, and is made up of 
creeping forms and those using the bottom as a breeding-place. 
REPRESENTATIVE ANIMALS OF THE SUBMERGED VEGETATION 
Fic. 75.—Upper fish, the green sunfish (Lepomis cyanellus); lower fish, the yellow 
perch (Perca flavescens); both juvenile; slightly reduced (original). 
Fic. 76.—A viviparous snail (Vivipara contectoides); natural size. 
Fic. 77.—A winter body or statoblast, of the gelatin-secreting polyzoan (Pectina- 
tella magnifica); 10 times natural size (original). 
Fic. 78.—A shrimp (Palaemonetes paludosus); twice natural size (original). 
b) Submerged vegetation association of the open waters—A lake of the 
coastal type is separated rapidly from the larger body of water in con- 
nection with which it is formed, or a morainic lake, when the ice retreats, 
