FIELD BOOK OF PONDS AND STREAMS 



beetles. On hot days the adults (Fig. 215) settle on stones 

 projecting from the midcurrents of rushing streams. They 

 are small, about a quarter of an inch long, and their bodies 

 are covered with silken hairs. These hold the film of air 

 which blankets the female when she climbs down over the 

 water-washed stones to lay her cluster of yellow eggs in the 

 swiftest part of the current. 



7 SL ^ 



Fig. 215. — P sephenus lecontei: i, adult; 2, its larva, 

 the water penny, dorsal side; 3, ventral side. 



The common eastern species, Psephenus lecontei {Psephen- 

 idcE), is knovv^n mostly by its larvas, for which Comstock 

 ft-st suggested the fitting name of water penny (Fig. 215). 

 These flat, copper-colored larvas cling tightly to the dark 

 under surfaces of water- washed rocks, and even when the 

 rocks have been upturned and they are right under the eye 

 they may not be seen at all. Only when the}'' are turned over 

 on their backs do water pennies display their legs and their 

 five pairs of glistening white gills (PI. VIII). Water pennies 

 may be found in shallow riffles all the year round, where they 

 feed upon the algal film on the stones (PI. I). 



The leaf-beetles, Family Chrysomelidae. — In this large fam- 

 ily of terrestrial leaf-eating beetles two subfamilies, the 

 DonaciincB and Galerucincs, feed upon water plants. The 

 commonest of these belong to the genus Donacia. 



Donacia. — The larvae of Dojtacia feed upon the under- 

 ground stems of various water plants such as the yellow water- 



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