178 A NATURALIST IN THE GREAT LAKES REGION 



so only about half the time, going ventral side up the other 

 half of the time. Eucrangonyx gracilis swims on its back all the 

 time. It is found in the old forest ponds. Another crustacean 

 inclosed in a bivalve shell like a small clam is found abundantly 

 on the bottom (Cypris, Fig. 56). The musk turtle is a frequent 

 and distinctive inhabitant of these chara ponds. Its odor is 



quite enough to distinguish it. 

 Chara ponds do not, as a rule, 

 support a varied or abundant 

 animal population, for the 

 chara is not an attractive food 

 plant. 



As the chara grows and 

 its lower layers decompose, 

 it forms peat rapidly, i or 

 2 inches a year, so that 

 ponds tend to fill up speedily. 

 Then flowering plants, with 

 submerged stems and leaves, 

 the latter much dissected, 

 replace the chara. Their 

 flowers are reared above the 

 surface. Such plants are mil- 

 foil, bladderwort, pond weed 

 (Fig. 64), and their associates, 

 to be described more in detail 

 in chapter xi. 



The nymph of the damsel fly, Ischnura verticalis (Fig. 195), 

 is quite characteristic of these milfoil ponds in the Dunes, 

 though it is a very widely distributed species elsewhere. The 

 nymph may be recognized by the fact that its gill plates end 

 in a long, tapering point and bear one or two dark crescentic 

 crossbands. 



The adult male of Ischnura verticalis is green with the top of 

 the abdomen black. The females may be either black or orange 



FIG. 197. Pennsylvania saxifrage, Saxl- 

 fraga pennsylvanica. 



